Building finish is that part of a project that typically completes the project but has nothing to do with the structural elements of the building. General practice divides the finish work into exterior (outside) and interior (inside) finish. Builders refer to this stage of construction to as finish carpentry. Other trade disciplines have a “Finish” stage to their contributions also. Both the electricians and plumbers have a “Rough-in” (nonstructural) and “Finish” element to their work.
The work on a building project is not complete when the foundation, framing, and sheathing are done. There are many finishes on a building that contribute to its durability, the comfort of its inhabitants, and its overall appearance It is your responsibility as the builder to coordinate with the other trades on the project, and to be aware of the details drawings and finish schedules throughout the project prints and specifications. This applies to everything from specifications for the foundation to details of the bathroom hardware.
When you have completed this course, you will be able to:
Exterior trim includes door and window trim, cornice trim, fascia boards and soffits, and rake or gable end trim. Contemporary designs with simple cornices and moldings contain little of this material; traditional designs have considerably more. Much of the exterior trim, in the form of finish lumber and moldings, is cut and fitted on the job. Other materials or assemblies, such as shutters, louvers, railings, or posts, are shop fabricated and arrive on the job ready to be fastened in place.
The properties desired in materials used for exterior trim are good painting and weathering characteristics, easy working qualities, and maximum freedom from warp. Decay resistance is desirable where materials may absorb moisture. Heartwood from cedar, cypress, and redwood has high decay resistance. Less durable species can be treated to make them decay resistant. Many manufacturers pre-dip materials, such as siding, window sash, door and window frames, and trim, with a water-repellent preservative. On the job dipping of end joints or miters cut at the building site is recommended when resistance to water entry and increased protection are desired.
Rust-resistant trim fastenings, whether nails or screws, are preferred wherever they may be in contact with weather. These include galvanized, stainless steel, or aluminum fastenings. When a natural finish is used, nails should be stainless steel or aluminum to prevent staining and discoloration. Cement-coated nails are not rust-resistant.
Siding and trim are normally fastened in place with a standard siding nail, which has a small flat head. Finish or casing nails might also be used for some purposes. Most of the trim along the shingle line, such as at gable ends and cornices, is installed before the roof shingles are applied.
The roof overhangs (eaves) are the portions of the roof that project past the side walls of the building. The cornice is the area beneath the overhangs. The upward slopes of the gable ends are called rakes. Several basic designs are used for finishing off the roof overhangs and cornices. Most of these designs come under the category of open cornice or closed cornice. They add to the attractiveness of a building and also help protect the side walls of the building from rain and snow. Wide overhangs also shade windows from the hot summer sun.
Cornice work includes the installation of the lookout ledger, lookouts, plancier (soffit), ventilation screens, fascia, frieze, and the moldings at and below the eaves, and along the sloping sides of the gable end (rake). The ornamental parts of a cornice are called cornice trim and consist mainly of molding; the molding running up the side of the rakes of a gable roof is called gable cornice trim. Besides the main roof, the additions and dormers may have cornices and cornice trim.
The type of cornice required for a particular structure is indicated on the wall sections of the drawings, and there are usually cornice detail drawings as well.
A roof with no rafter overhang or eave usually has the simple cornice shown in Figure 1. This cornice consists of a single strip or board called a frieze. It is beveled on the upper edge to fit under the overhang or eave and rabbeted on the lower edge to overlap the upper edge of the top course of siding. If trim is used, it usually consists of molding placed as shown in Figure 1.
Molding trim in this position is called crown molding. A roof with a rafter overhang may have an open cornice or a closed (also called a box) cornice.
Figure 1 – Simple cornice.
In open cornice construction shown in Figure 2, the undersides of the rafters and roof sheathing are exposed.
Figure 2 – Open cornice.
A nailing header (fascia backer) is nailed to the tail ends of the rafters to provide a straight and solid nailing base for the fascia board. Most spaces between the rafters are blocked off. Some spaces are left open (and screened) to allow attic ventilation. Usually, a frieze board is nailed to the wall below the rafters. Sometimes the frieze board is notched between the rafters and molding is nailed over it. Molding trim in this position is called bed molding.
In closed cornice construction, the bottom of the roof overhang is closed off. The two most common types of closed cornices are the flat boxed cornice and the sloped boxed cornice.
The flat box cornice requires framing pieces called lookouts. These are toenailed to the wall or to a lookout ledger and face nailed to the ends of the rafters. The lookouts provide a nailing base for the soffit, which is the material fastened to the underside of the cornice. A typical flat box cornice is shown in Figure 3.
For a sloped box cornice, the soffit material is nailed directly to the underside of the rafters as shown in Figure 4. This design is often used on buildings with wide overhangs.
The basic rake trim pieces are the frieze board, trim molding, and the fascia and soffit material. Figure 5 shows the finish rake for a flat box cornice. It requires a cornice return where the eave and rake soffits join. Figure 6 shows the rake of a sloped box cornice. Always use rust-resistant nails for exterior finish work. They may be aluminum, galvanized, or cadmium-plated steel.
Because cornice construction is time consuming, various prefabricated systems are available that provide a neat, trim appearance. Cornice soffit panel materials include plywood, hardboard, fiberboard, and metal. Many of these are factory primed and available in a variety of standard widths, 12 to 48 inches, and in lengths up to 12 feet. They also may be equipped with factory-installed screen vents.
When installing large sections of wood fiber panels, you should fit each panel with clearance for expansion. Nail 4d rust-resistant nails 6 inches apart along the edges and intermediate supports (lookouts). Strut nailing at the end butted against a previously placed panel. First, nail the panel to the main supports and then along the edges. Drive nails carefully so the underside of the head is just flush with the panel surface. Remember, this is finish work; no hammer head marks, please. Always read and follow manufacturer’s directions and recommended installation procedures. Cornice trim and soffit systems are also available in aluminum and come in a variety of prefinished colors and designs.
Soffit systems made of prefinished metal panels and attachment strips are common. They consist of three basic components: wall hanger strips (also called frieze strips), soffit panels (solid, vented, or combination), and fascia covers. Figure 7 shows the typical installation configuration of the components. Soffit panels include a vented area and are available in a variety of lengths.
Figure 7 – Basic components of a prefinished metal soffit system.
To install a metal panel system, first snap a chalk line on the sidewall level with the bottom edge of the fascia board. Use this line as a guide for nailing the wall hanger strip in place. Insert the panels, one at a time, into the wall strip. Nail the outer end to the bottom edge of the fascia board.
After all soffit panels are in place, cut the fascia cover to length and install it. The bottom edge of the cover is hooked over the end of the soffit panels. It is then nailed in place through prepunched slots located along the top edge. Remember to use nails compatible with the type of material being used to avoid electrolysis between dissimilar metals. Again, always study and follow the manufacturer’s directions when making an installation of this type.
Test your Knowledge
1. Which of the following wood characteristics is least important when selecting trim material?
- A. Knots
- B. Even grain
- C. Natural decay resistance
- D. Preservative pretreatment
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Though lath and plaster finish is still used in building construction today, drywall finish has become the most popular. Drywall finish saves time in construction, whereas plaster finish requires drying time before other interior work can be started. Drywall finish requires only short drying time since little, if any, water is required for application. However, a gypsum drywall demands a moderately low moisture content of the framing members to prevent “nail-pops.” Nail-pops result when frame members dry out to moisture equilibrium, causing the nail head to form small “humps” on the surface of the board. Stud alignment is also important for single layer gypsum finish to prevent a wavy, uneven appearance. Thus, there are advantages to both plaster and gypsum drywall finishes, and each should be considered along with the initial cost and maintenance.
There are many types of drywall. One of the most widely used is gypsum board in 4 by 8 foot sheets. Gypsum board is also available in lengths up to 16 feet. These lengths are used in horizontal application. Plywood, hardboard, fiberboard, particleboard, wood paneling, and similar types are also used. Many of these drywall finishes come prefinished.
The use of thin sheet materials, such as gypsum board or plywood, requires that studs and ceiling joists have good alignment to provide a smooth, even surface. Wood sheathing often corrects misaligned studs on exterior walls. A strongback shown in Figure 8 provides for alignment of ceiling joists of unfinished attics. It can also be used at the center of a span when ceiling joists are uneven.
Figure 8 – Strongback for alignment of ceiling joists.
Gypsum wallboard is the most commonly used wall and ceiling covering in construction today. Because gypsum is nonflammable and durable, it is appropriate for application in most building types. Sheets of drywall are nailed or screwed into place, and nail indentions or “dimples” are filled with joint compound. Joints between adjoining sheets are built up with special tape and several layers (usually three) of joint compound. Drywall is easily installed, though joint work can be tedious.
Drywall varies in composition, thickness, and edge shape. The most common sizes with tapered edges are 1/2 inch by 4 feet by 8 feet and 1/2 inch by 4 feet by 12 feet.
Regular gypsum board is commonly used on walls and ceilings and is available in various thicknesses. The most common thicknesses are 1/2 inch and 5/8 inch. Type X gypsum board has special additives that make it fire-resistant.
MR (moisture-resistant) or WR (water-resistant) board is also called greenboard and blueboard. Being water-resistant, this board is appropriate for bathrooms, laundries, and similar areas with high moisture. It also provides a suitable base for embedding tiles in mastic. MR or WR board is commonly 1/2 inch thick.
Sound-deadening board is a sublayer used with other layers of drywall (usually type X); this board is often 1/4 inch thick.
Backing board has a gray paper lining on both sides. It is used as a base sheet on multilayer applications. Backing board is not suited for finishing and decorating.
Foil-backed board serves as a vapor barrier on exterior walls. This board is available in various thicknesses.
Vinyl-surfaced board is available in a variety of colors. It is attached with special drywall finish nails and is left exposed with no joint treatment.
Plasterboard or gypsum lath is used for plaster base. It is available in thickness starting at 3/8 inch, with widths of 16 and 24 inches, and lengths usually of 48 inches. Because of its availability in manageable sizes, it is widely used as a plaster base instead of metal or wood lath for both new construction and renovation. This material is not compatible with Portland cement plaster.
The varying lengths of drywall allow you to lay out sheets so that the number of seams is kept to a minimum. End points can be a problem since the ends of the sheets are not shaped; only the sides are. As sheet length increases, so does weight, unwieldiness, and the need for helpers. Standard lengths are 8, 9, 10, 12, and 14 feet. Sixteen-foot lengths are also available. Use the thickness that is right for the job. One-half inch drywall is the dimension most commonly used. That thickness, which is more than adequate for studs 16 inches on center (OC), is also considered adequate where studs are 24 inches OC. Where ceiling joists are 16 inches OC, use 1/2 inch drywall, whether it runs parallel or perpendicular to joists. Where ceiling joists are 24 inches OC, though, use 1/2 inch drywall only if the sheets are perpendicular to joists.
Drywall of 1/4 and 3/8 inch thicknesses is used effectively in renovation to cover existing finish walls with minor irregularities. Neither is adequate as a single layer for walls or ceiling, however. Two 1/4 inch-thick plies are also used to wrap curving walls. Drywall of 5/8 inch thickness is favored for quality single layer walls, especially where studs are 24 inches OC. Use 5/8 inch drywall for ceiling joists 24 inches OC, where sheets run parallel to joists. This thickness is widely used in multiple, fire-resistant combinations.
There are several types of edging in common use. Tapered allows joint tape to be bedded and built up to a flat surface. This is the most commonly used edge. Tapered round is a variation on this type. Tapered round edges allow better joints. These edges are more easily damaged, however. Square makes an acceptable exposed edge. Beveled has an edge that, when left untaped, gives a paneled look.
Commonly used tools in drywall application include a tape measure, a chalk line, a level, utility and drywall knives, a straightedge, and a 48 inch T square (drywall square) or framing square. Other basic tools include a keyhole saw, drywall hammer (or convex head hammer), screw gun, drywall trowel, comer trowel, and foot lift.
A tape measure, chalk line, and level are used for layout work. Utility and drywall knives, a straightedge, and squares are used for scoring and breaking drywall. A keyhole saw is used for cutting irregular shapes and openings, such as outlet box openings. A convex head, or drywall, hammer used for drywall nails will “dimple” the material without tearing the paper. A screw gun quickly sinks drywall screws to the adjusted depth and then automatically disengages. Several of these tools are shown in Figure 9.
Figure 9 – T square, drywall hammer, and screw gun.
A foot lift, shown in Figure 10, helps you raise and lower drywall sheets while you plumb the edges. Be careful when using the foot lift, as applying too much pressure to the lift can damage the drywall.
Figure 10 – Foot lift.
Drywall knives, shown in Figure 11, have a variety of uses. A 6 inch knife is used to bed the tape in the first layer of joint compound and to fill nail or screw dimples. A 12 inch finishing knife feathers out the second layer of joint compound and is usually adequate for the third or topping layer. Knives 16 inches and wider are used for applying the topping coat. Clean and dry drywall knives after use. Use drywall knives only for the purpose intended, to finish drywall.
Figure 11 – Drywall knives.
The drywall trowel shown in Figure 12 resembles a concrete finishing trowel and is manufactured with a 3/16 inch concave bow. This trowel, also referred to as a flaring, feathering, or bow trowel, is used when applying the finish layer of joint compound. A corner trowel, shown in Figure 12, is almost indispensable for making clean interior comers.
For sanding dried joint compound smooth, use 220 grit sandpaper. Sandpaper should be wrapped around a sanding block or can be used on an orbital sander. When sanding, ensure you’re wearing the required personnel protective gear to prevent dust inhalation.
Figure 12 – Trowels for drywalling.
Which fasteners you use depends in part on the material underneath. The framing is usually wood or metal studs, although gypsum is occasionally used as a base. Adhesives are normally used in tandem with screws or nails. This combination allows the installer to use fewer screws or nails, leaving fewer holes that require filling. For reasons noted shortly, you will find the drywall screw the most versatile fastener for attaching drywall to framing members.
Figure 13 – Drywall nails.
Drywall nails shown in Figure 13 are specially designed with oversized heads for greater holding power. Casing or common nail heads are too small. Further, untreated nails can rust and stain a finish. The drywall nail most frequently used is the annular ring nail. This nail fastens securely into wood studs and joists. When purchasing such nails, consider the thickness of the layer or layers of drywall, and allow additional length for the nail to penetrate the underlying wood 3/4 inch. Example: 1/2 inch drywall plus 3/4 inch penetration requires a 1 1/4 inch nail. A longer nail does not fasten more securely than one properly sized, and the longer nail is subject to the expansion and contraction of a greater depth of wood. Smooth shank, diamond head nails are commonly used to attach two layers of drywall, for example, when fireproofing a wall. Again, the mil length should be selected carefully.
Smooth shank nails should penetrate the base wood 1 inch. Predecorated drywall nails, which may be left exposed, have smaller heads and are color matched to the drywall.
Drywall screws shown in Figure 14 are the preferred method of fastening among professional builders, cabinetmakers, and renovators. These screws are made of high quality steel and are superior to conventional wood screws. Use a power screw gun or an electric drill to drive in the screws. Because this method requires no impact, there is little danger of jarring loose earlier connections. There are two types of drywall screws commonly used: type S and type W.
Figure 14 – Drywall screws.
Type S screws, shown in Figure 14, are designed for attachment to metal studs. The screws are self tapping and very sharp, since metal studs can flex away. At least 3/8 inch of the threaded part of the screw should pass through a metal stud. Although other lengths are available, 1 inch type S screws are commonly used for single ply drywall.
Type W screws, shown in Figure 14, hold drywall to wood. They should penetrate studs or joists at least 5/8 inch. If you are applying two layers of drywall, the screws holding the second sheet need to penetrate the wood beneath only 1/2 inch.
Joint tape varies little. The major difference between tapes is whether they are perforated or not. Perforated types are somewhat easier to bed and cover. New self-sticking fiber mesh types that resemble window screen are becoming popular. The mesh design and self-sticking factor eliminate the need for the first layer of bedding joint compound.
Joint compound comes ready mixed or in powder form. The powder form must be mixed with water to a putty consistency. Ready mixed compound is easier to work with, although its shelf life is shorter than the powdered form. Joint compounds vary according to the additive they contain. Always read and follow the manufacturer’s specifications.
Adhesives are used to bond single-ply drywall directly to framing members, furring strips, masonry surfaces, insulation board, or other drywall. They must be used with nails or screws. Because adhesives are matched with specific materials, be sure to select the correct adhesive for the job. Read and follow the manufacturer’s directions.
A number of metal accessories have been developed to finish off or protect drywall. Corner beads, shown in Figure 15, are used on all exposed comers to ensure a clean finish and to protect the drywall from edge damage. Corner bead is nailed or screwed every 5 inches through the drywall and into the framing members. Be sure the corner bead stays plumb as you fasten it in place.
Figure 15 – Corner bead.
Casing beads, also called stop beads, shown in Figure 16, are used where drywall sheets abut at wall intersections, wall and exposed ceiling intersections, or where otherwise specified. Casing beads are matched to the thickness of the drywall used.
Figure 16 – Casing beads.
When laying out a drywall job, keep in mind that each joint will require taping and sanding. You should arrange the sheets so that there will be a minimum of joint work. Choose drywall boards of the maximum practical length.
Drywall can be hung with its length either parallel or perpendicular to joists or studs. Although both arrangements work, sheets running perpendicular afford better attachment. In double-ply installation, run base sheets parallel and top sheets perpendicular. For walls, the height of the ceiling is an important factor. When ceilings are 8 feet 1 inch high or less, run wall sheets horizontally. Where they are higher, run wall sheets vertically, as shown in Figure 17.
Figure 17 – Single layer application of drywall.
The sides of drywall taper, but the ends do not, so there are some layout constraints. End joints must be staggered where they occur. Such joints are difficult to feather out correctly. Where drywall is hung vertically, avoid side joints within 6 inches of the outside edges of doors or windows. In the case of windows, the bevel on the side of the drywall interferes with the finish trim, and the bevel may be visible. To avoid this difficulty, lay out vertical joints so they meet over a cripple (shortened) stud toward the middle of a door or window opening.
When installing drywall horizontally and an impact-resistant joint is required, you should use nailing blocks as shown in Figure 17.
There are several things you can do to make working with drywall easier.
First, don’t order drywall too far in advance. Drywall must be stored flat to prevent damage to the edges, and it takes up a lot of space.
Figure 18 – Cutting gypsum drywall.
Second, to cut drywall you only need to cut through the fine paper surface (view A) as shown in Figure 18. Then grasp the smaller section and snap it sharply (view B). The gypsum core breaks along the scored line. Cut through the paper on the back (view C).
Third, when cutting a piece to length, never cut too closely. One half inch gaps are acceptable at the top and the bottom of a wall because molding covers these gaps. If you cut too closely, you may have difficulty getting the piece into place. Where walls are not square, you may have to trim anyway.
Fourth, snap chalk lines on the drywall to indicate joists or stud centers underneath for quicker attachment. Drywall edges must be aligned over stud, joist, or rafter centers.
Fifth, when cutting out holes for outlet boxes, fixtures, and so on, measure from the nearest fixed point(s), for example, from the floor or edge of the next piece of drywall. Take two measurements from each point, so you get the true height and width of the cutout. Locate the cutout on the finish side of the drywall. To start the cut, either drill holes at the corners or start cuts by stabbing the sharp point of the keyhole saw through the drywall and then finishing the cutting with a keyhole or compass saw. It is more difficult to cut a hole with just a utility knife, but it can be done.
When attaching drywall, hold it firmly against the framing to avoid nail pops and other weak spots. Nails or screws must fasten securely in a framing member. If a nail misses the framing, pull it out, dimple the hole, fill it in with compound, and then try again. If you drive a nail in so deep that the drywall is crushed, drive in another reinforcing nail within 2 inches of the first.
Nail or screw drywall from the center of the sheet outward. Where you double nail sheets, single nail the entire sheet first and then add the second (double) nails, again beginning in the middle of the sheet and working outward.
Sheets are single or double nailed. Single nails are spaced a maximum of 8 inches apart on walls and 7 inches apart on ceilings. Where sheets are double nailed, the centers of nail pairs should be approximately 12 inches apart. Space each pair of nails 2 to 2 1/2 inches apart. Do not double nail around the perimeter of a sheet. Instead, nail as shown in Figure 19.
Figure 19 – Spacing for single and double nailing of gypsum drywall.
As you nail, it is important that you dimple each nail, that is, drive each nail in slightly below the surface of the drywall without breaking the surface of the material. Dimpling creates a pocket that can be filled with joint compound. Although special convex headed drywall hammers are available for this operation, a conventional claw hammer also works, as shown in Figure 20.
Figure 20 – Dimpling of gypsum drywall.
Because screws attach more securely, fewer are needed. Screws are usually spaced 12 inches OC regardless of drywall thickness. On walls, screws may be placed 16 inches OC for greater economy, without loss of strength. Do not double up screws except where the first screw seats poorly. Space screws around the edges the same as nails.
Adhesive applied to wood studs allows you to bridge minor irregularities along the studs and to use about half the number of nails. When using adhesives, you can space the nails 12 inches apart without doubling up. Do not alter nail spacing along end seams, however. To attach sheets to studs, use a caulking gun and run a 3/8 inch bead down the middle of the stud. Where sheets meet over a framing member, run two parallel beads. Do not make serpentine beads, as the adhesive could ooze out onto the drywall surface. If you are laminating a second sheet of drywall over a fret, roll liquid contact cement with a short snap roller on the face of the sheet already in place. To keep adhesive out of your eyes, wear goggles. When the adhesive turns dark, usually within 30 minutes, it is ready to receive the second piece of drywall. Screw on the second sheet as described above.
Begin by attaching sheets on the ceiling, first checking to be sure extra blocking that will receive nails or screws is in place above the top plates of the walls. By doing the ceiling first, you have maximum exposure of blocking to nail or screw into. If there are gaps along the intersection of the ceiling and wall, it is much easier to adjust wall pieces.
Ceilings can be covered by one person using two tees made from 2 by 4s. This practice is acceptable when dealing with sheets that are 8 foot in length. Sheets over this length **17 will require a third tee, which is very awkward for one individual to handle. Two people should be involved with the installation of drywall on ceilings.
Walls are easier to hang than ceilings, and one person can work alone effectively, although the job goes faster if two people work together. As you did with the ceiling, be sure the walls have sufficient blocking in corners before you begin.
Make sure the first sheet on a wall is plumb and its leading edge is centered over a stud. Then, all you have to do is align successive sheets with the first sheet. The foot lift shown earlier in Figure 10 is useful for raising or lowering a sheet while you level its edge. After you have sunk two or three screws or nails, the sheet will stay in place. A gap of 1/2 inch or so along the bottom of a sheet is not critical; it is easily covered by finish flooring, baseboards, and so on. If you favor a clean, modem line without trim, manufactured metal or vinyl edges, called casing beads, are available for finishing the edges.
During renovation, you may find that hanging sheets horizontally makes sense. Because studs in older buildings often are not on regular centers, the joints of vertical sheets frequently do not align with the studs. Using the foot lift, level the top edge of the bottom sheet. Where studs are irregular, it is even more important that you note positions and chalk line stud centers onto the drywall face before hanging the sheet.
Applying drywall in older buildings yields a lot of waste because framing is not always standardized. Use the cutoffs in such out-of-the-way places as closets. Do not piece together small sections in areas where you will notice seams. Never assume that ceilings are square with walls. Always measure from at least two points, and cut accordingly.
Drywall is quite good for creating or covering curved walls. For the best results, use two layers or 1/4 inch drywall, hung horizontally. The framing members of the curve should be placed at intervals of no more than 16 inches OC; 12 inches is better. For an 8 foot sheet applied horizontally, an arc depth of 2 to 3 feet should be no problem, but do check the manufacturer’s specifications. Sharper curves may require backcutting (scoring slots into the back so that the sheet can be bent easily) or wetting (wet sponging the front and back of the sheet to soften the gypsum). Results are not always predictable, though. When applying the second layer of 1/4 inch drywall, stagger the vertical butt joints.
Finishing gypsum board drywall is generally a three coat application. Attention to drying times between coats prevents rework that involves cost as well as extra time.
Where sheets of drywall join, cover the joints with joint tape and compound as shown in Figure 21. The procedure is straightforward.
Figure 21 – Finishing drywall joints.
Figure 22 – Finishing an inside corner.
When finishing an inside corner as shown in Figure 22, cut your tape the length of the corner angle you are going to finish. Apply the joint compound evenly with a 4 inch knife about 2 inches on each side of the angle. Use sufficient compound to embed the tape. Fold the tape along the center crease as in view A and firmly press it into the corner. Use enough pressure to squeeze some compound under the edges. Feather the compound 2 inches from the edge of the tape as shown in view B. When the first coat is dry, apply a second coat. A corner trowel shown in view C is almost indispensable for taping comers. Feather the edges of the compound 1 1/2 inches beyond the first coat. Apply a third coat if necessary, let it dry, and sand it to a smooth surface. Use as little compound as possible at the apex of the angle to prevent hairline cracking. When molding is installed between the wall and ceiling intersection, it is not necessary to tape the joint, as shown in view D.
Figure 23 – Finishing an outside corner.
When finishing an outside corner, as shown in Figure 23, be sure the corner bead is attached firmly. Using a 4 inch finishing knife, spread the joint compound 3 to 4 inches wide from the nose of the bead, covering the metal edges. When the compound is completely dry, sand lightly and apply a second coat, feathering edges 2 to 3 inches beyond the first coat. A third coat may be needed, depending on your coverage. Feather the edges of each coat 2 or 3 inches beyond each preceding coat. Corner beads are no problem if you apply compound with care and scrape the excess clean. Nail holes and screw holes usually can be covered in two passes, though shrinkage sometimes necessitates three. A tool that works well for sanding hard to reach places is a sanding block on an extension pole; the block has a swivel head joint.
To give yourself the greatest number of decorating options in the future, paint the finished drywall surface with a coat of flat oil base primer. Whether you intend to wallpaper or paint with latex, oil base primer adheres best to the facing of the paper and seals it.
For the best results, drywall should be flat against the surface to which it is being attached. How flat the nailing surface must be depends upon the desired finish effect. Smooth painted surfaces with spotlights on them require as nearly flawless a finish as you can attain. Similarly, delicate wall coverings, particularly those with close, regular patterns, accentuate pocks and lumps underneath. Textured surfaces are much more forgiving. In general, if adjacent nailing elements such as studs vary by more than 1/4 inch, build up low spots. There are three ways to create a flat nailing surface:
By stretching strings taut between diagonal comers, you can get a quick idea of any irregularities in a wall. If studs are exposed, further assess the situation with a level held against a straight 2 by 4. Hold the straightedge plumb in front of each stud and mark low spots every 12 inches or so. Using a builder’s crayon, write the depth of each low spot, relative to the straightedge, on the stud. If studs aren’t exposed, locate each stud by test drilling and inserting a bent coat hanger into the hole. Chalk line the center of each stud on the existing surface. Here too, mark the depth of low spots.
The objective of this process is a flat plane of furring strips over existing studs. Tack the strips in place and add shims (wood shingles are best) at each low spot marked, as shown in Figure 24. To make sure a furring strip does not skew, use two shims, with their thin ends reversed, at each point. Tack the shims in place and plumb the furring strips again. When you are satisfied, drive the nails or screws all the way in.
Figure 24 – Furring strips backed with shims.
When attaching the finish sheets, use screws or nails long enough to penetrate through furring strips and into the studs behind. Strips directly over studs ensure the strongest attachment. Where finish materials are not sheets (for example, single board vertical paneling), furring should run perpendicular to the studs.
Regardless of type, finish material must be backed firmly at all nailing points, corners, and seams. Where you cover existing finish surfaces or otherwise alter the thickness of walls, it is usually necessary to build up existing trim. Figure 25 shows how this might be done for a window casing. Electrical boxes must also be extended with box extensions or plaster rings.
Figure 25 – Building up an interior window casing.
Masonry surfaces must be smooth, clean, and dry. Where the walls are below grade, use mastic to attach a vapor barrier of polyethylene and install the furring strips. Use a powder-actuated nail gun to attach strips to the masonry. Follow all safety procedures. If you hand nail, drive case-hardened nails into the mortar joints. Wear goggles, as these nails can fragment.
Most drywall blemishes are caused by structural shifting or water damage. Correct any underlying problems before attacking the symptoms.
Popped up nails are easily fixed by pulling them out or by dimpling them with a hammer. Test the entire wall for springiness and add nails or screws where needed. Within 2 inches of a popped up nail, drive in another nail. Spackle both nails when the spots are dry, then sand and prime.
To repair cracks in drywall, cut back the edges of the crack slightly to remove any crumbly gypsum and to provide a good depression for a new filling of joint compound. Feather the edges of the compound. When dry, sand and prime them.
When a piece of drywall tape lifts, gently pull until the piece rips free from the part that’s still well stuck. Sand the area affected and apply a new bed of compound for a replacement piece of tape. The self-sticking tape mentioned earlier works well here. Feather all edges.
If a sharp object has dented the drywall, merely sand around the cavity and fill it with spackling compound. A larger hole, bigger than your fist, should have a backing. One repair method is shown in Figure 26.
Figure 26 – Repairing a large hole in drywall.
First, cut the edges of the hole clean with a utility knife as shown in view A. The piece of backing should be somewhat larger than the hole itself. Drill a small hole into the middle of the backing piece and thread a piece of wire into the hole. This wire allows you to hold the piece of backing in place. Spread mastic around the edges of the backing. When the adhesive is tacky, fit the backing diagonally into the hole as shown in view B and, holding onto the wire, pull the piece against the back side of the hole. When the mastic is dry, push the wire back into the wall cavity. The backing stays in place. Fill the hole with plaster or joint compound as shown in view C and finish as shown in view D.
This is just one of several options available for repairing large surface damage to gypsum board.
Compound sags in holes that are too big. If this happens, mastic a replacement piece of drywall to the backing piece. To avoid a bulge around the filled in hole, feather the compound approximately 16 inches, or more. If the original drywall is 1/2 inch thick use 3/8 inch plasterboard as a replacement on the backing piece.
Holes larger than 8 inches should be cut back to the centers of the nearest studs. Although you should have no problem nailing a replacement piece to the studs, the top and the bottom of the new piece must be backed. The best way to install backing is to screw drywall gussets (supports) to the back of the existing drywall. Then put the replacement piece in the hole and screw it to the gussets.
Test your Knowledge
2. When you are attaching drywall, what is the recommended nailing procedure?
- A. Start at the top and work down.
- B. Start at the side joining the previous sheet and work across.
- C. Start at the center and work out.
- D. Start at the bottom and work up.
- Return to Table of Contents -
Plaster and stucco are like concrete in that they are construction materials applied in a plastic condition that harden in place. They are also basically the same material. The fundamental difference between the two is location. If used internally, the material is called plaster; if used externally, it is called stucco.
A plaster mix, like a concrete mix, is made plastic by the addition of water to dry ingredients, including binders and aggregates. Also like in concrete, a chemical reaction of the binder and the water, called hydration, causes the mix to harden.
The binders most commonly used in plaster are gypsum, lime, and Portland cement. Because gypsum plaster should not be exposed to water or severe moisture conditions, it is usually restricted to interior use. Lime and Portland cement plaster may be used both internally and externally. The most commonly used aggregates are sand, vermiculite, and perlite.
Gypsum is a naturally occurring sedimentary gray, white, or pink rock. The natural rock is crushed, and then heated to a high temperature. This process, known as calcining, drives off about three quarters of the water of crystallization, which forms about 20 percent of the weight of the rock in its natural state. The calcined material is then ground to a fine powder. Additives are used to control set, stabilization, and other physical or chemical characteristics.
For a type of gypsum plaster called Keene’s cement, the crushed gypsum rock is heated until nearly all the crystallization water is removed. The resulting material, called Keene’s cement, produces a very hard, fine textured finish coat.
The removal of crystallization water from natural gypsum is a dehydration process. In the course of setting, mixing water (water of hydration) added to the mix dehydrates with the gypsum, causing recrystallization. Recrystallization results in hardening of the plaster.
There are four common types of gypsum base coat plasters. Gypsum neat plaster is gypsum plaster without aggregate, intended for mixing with aggregate and water on the job. Gypsum ready mixed plaster consists of gypsum and ordinary mineral aggregate.
On the job, you just add water. Gypsum wood fibered plaster consists of calcined gypsum combined with at least 0.75 percent by weight of nonstaining wood fibers. It may be used as is or mixed with one part sand to produce base coats of superior strength and hardness. Gypsum bond plaster is designed to bond to properly prepared monolithic concrete. This type of plaster is basically calcined gypsum mixed with from 2 to 5 percent lime by weight.
There are five common types of gypsum finish coat plasters.
Lime is obtained principally from the calcining of limestone, a very common mineral. Chemical changes occur that transform the limestone into quicklime, a very caustic material. When it comes in contact with water, a violent reaction, hot enough to boil the water, occurs.
Today, the lime manufacturers slake the lime as part of the process of producing lime for mortar. Slaking is done in large tanks where water is added to convert the quicklime to hydrated lime without saturating it with water. The hydrated lime is a dry powder with just enough water added to supply the chemical reaction. Hydration is usually a continuous process and is done in equipment similar to that used in calcining. After the hydrating process, the lime is pulverized and bagged. When received by the plasterer, hydrated lime still requires soaking with water.
In mixing medium slaking and slow slaking limes, you should add the water to the lime. Slow slaking lime must be mixed under ideal conditions. It is necessary to heat the water. Magnesium lime is easily drowned, so be careful not to add too much water to quick slaking calcium lime. When too little water is added to calcium and magnesium limes, they can be burned. Whenever lime is burned or drowned, a part of it is spoiled. It will not harden and the paste will not be as viscous and plastic as it should be. To produce plastic lime putty, soak the quicklime for an extended period, as much as 21 days.
Because of the delays involved in the slaking process of quicklime, most building lime is the hydrated type. Normal hydrated lime is converted into lime putty by soaking it for at least 16 hours. Special hydrated lime develops immediate plasticity when mixed with water and may be used right after mixing. Like calcined gypsum, lime plaster tends to return to its original rock like state after application.
For interior base coat work, lime plaster has been largely replaced by gypsum plaster. Lime plaster is now used mainly for interior finish coats. Because lime putty is the most plastic and workable of the cementitious materials used in plaster, it is often added to other less workable plaster materials to improve plasticity. For lime plaster, lime (in the form of either dry hydrate or lime putty) is mixed with sand, water, and a gauging material. The gauging material is intended to produce early strength and to counteract shrinkage tendencies. It can be either gypsum gauging plaster or Keene’s cement for interior work or Portland cement for exterior work. When using gauging plaster or Keene’s cement, mix only the amount you can apply within the initial set time of the material.
Portland cement plaster is similar to the Portland cement mortar used in masonry. Although it may contain only cement, sand, and water, lime or some other plasterizing material is usually added for butteriness.
Portland cement plaster can be applied directly to exterior and interior masonry walls and over metal lath. Never apply Portland cement plaster over gypsum plasterboard or over gypsum tile. Portland cement plaster is recommended for use in plastering walls and ceilings of large walk in refrigerators and cold storage spaces, basements, toilets, showers, and similar areas where an extra hard or highly water-resistant surface is required.
As mentioned earlier, there are three main aggregates used in plaster: sand, vermiculite, and perlite. Less frequently used aggregates are wood fiber and pumice.
Sand for plaster, like sand for concrete, must contain no more than specified amounts of organic impurities and harmful chemicals. Tests for these impurities and chemicals are conducted by Engineering Aids.
Proper aggregate gradation influences plaster strength and workability. It also has an effect on the tendency of the material to shrink or expand while setting. Plaster strength is reduced if excessive fine aggregate material is present in a mix. The greater quantity of mixing water required raises the water cement ratio, thereby reducing the dry set density. The cementitious material becomes overextended since it must coat a relatively larger overall aggregate surface. An excess of coarse aggregate adversely affects workability; the mix becomes harsh working and difficult to apply.
Plaster shrinkage during drying can be caused by an excess of either fine or coarse aggregate. You can minimize this problem by properly proportioning the raw material, and using good, sharp, properly size graded sand.
Generally, any sand retained on a No. 4 sieve is too coarse to use in plaster. Only a small percentage of the material, about 5 percent, should pass the No. 200 sieve.
Vermiculite is a micaceous mineral in which each particle is laminated or made up of adjoining layers. When vermiculite particles are exposed to intense heat, steam forms between the layers, forcing them apart. Each particle increases from 6 to 20 times in volume. The expanded material is soft and pliable with a color varying between silver and gold.
For ordinary plasterwork vermiculite is used only with gypsum plaster; its use is generally restricted to interior applications. For acoustical plaster, vermiculite is combined with a special acoustical binder.
The approximate dry weight of a cubic foot of 1:2 gypsum vermiculite plaster is 50 to 55 pounds. The dry weight of a cubic foot of comparable sand plaster is 104 to 120 pounds.
Raw perlite is a volcanic glass that, when flash roasted, expands to form irregularly shaped frothy particles containing innumerable minute air cells. The mass is 4 to 20 times the volume of the raw particles. The color of expanded perlite ranges from pearly white to grayish white.
Perlite is used with calcined gypsum or Portland cement for interior plastering. It is also used with special binders for acoustical plaster. The approximate dry weight of a cubic foot of 1:2 gypsum perlite plaster is 50 to 55 pounds, or about half the weight of a cubic foot of sand plaster.
Although sand, vermiculite, and perlite make up the great majority of plaster aggregate, other materials, such as wood fiber and pumice, are also used. Wood fiber may be added to neat gypsum plaster at the time of manufacture to improve its working qualities. Pumice is a naturally formed volcanic glass similar to perlite, but heavier: 28 to 32 pounds per cubic foot versus 7.5 to 15 pounds for perlite. The weight differential gives perlite an economic advantage and limits the use of pumice to localities near where it is produced.
In plaster, mixing water performs two functions. First, it transforms the dry ingredients into a plastic, workable mass. Second, it combines with the binder to induce hardening. As with concrete, there is a maximum quantity of water per unit of binder required for complete hydration; an excess over this amount reduces the plaster strength.
In all plaster mixing, though, more water is added than is necessary for complete hydration of the binder. The excess is necessary to bring the mix to workable consistency. The amount to be added for workability depends on several factors: the characteristics and age of the binder, application method, drying conditions, and the tendency of the base to absorb water. A porous masonry base, for example, draws a good deal of water out of a plaster mix. If this reduces the water content of the mix below the maximum required for hydration, incomplete curing will result.
Add only the amount of water required to attain workability to a mix. The water should be potable and contain no dissolved chemicals that might accelerate or retard the set. Never use water previously used to wash plastering tools for mixing plaster. It may contain particles of set plaster that could accelerate setting. Avoid stagnant water; it may contain organic material that can retard setting and possibly cause staining.
There must be a continuous surface to which the plaster can be applied and to which it will cling, the plaster base. A continuous concrete or masonry surface may serve as a base without further treatment.
For plaster bases, such as those defined by the inner edges of the studs or the lower edges of the joists, a base material called lath must be installed to form a continuous surface spanning the spaces between the structural members.
Wood lath is made of white pine, spruce, fir, redwood, and other soft, straight grained woods. The standard size of wood lath is 5/16 inch by 1 1/2 inches by 4 feet. Each lath is nailed to the studs or joists with 3 penny (3d) blued lathing nails.
Laths are nailed six in a row, one above the other. The next six rows of lath are set over two stud places. The joints of the lath are staggered in this way so cracks will not occur at the joinings. Lath ends should be spaced 1/4 inch apart to allow movement and prevent buckling. Figure 27 shows the proper layout of wood lath. To obtain a good key (space for mortar), space the laths not less than 3/8 inch apart.
Figure 27 – Wood lath with joints staggered every sixth course.
Figure 28 shows good spacing with strong keys. Wood laths come 50 to 100 to the bundle and are sold by the thousand. The wood should be straight-grained, and free of knots and excessive pitch. Do not use old lath; dry or dirty lath offers a poor bonding surface. Lath must be damp when the mortar is applied. Dry lath pulls the moisture out of the mortar, preventing proper setting. The best method to prevent dry lath is to wet it thoroughly the day before plastering. This lets the wood swell and reach a stable condition ideal for plaster application.
Figure 28 - Wood lath with keys.
Of the many kinds of lathing materials available, board lath is the most widely used today. Board lath is manufactured from mineral and vegetable products. It is produced in board form, and in sizes generally standardized for each application to studs, joists, and various types of wood and metal timing.
Board lath has a number of advantages. It is rigid, strong, stable, and reduces the possibility of dirt filtering through the mortar to stain the surface. It is insulating and strengthens the framework structure. Gypsum board lath is fire-resistant. Board lath also requires the least amount of mortar to cover the surface.
Board laths are divided into two main groups, gypsum board and insulation board. Gypsum lath is made in a number of sizes, thicknesses, and types. Each type is used for a specific purpose or condition.
Only gypsum mortar can be used over gypsum lath. Never apply lime mortar, Portland cement, or any other binding agent to gypsum lath.
The most commonly used size gypsum board lath is the 3/8 inch by 16 inches by 48 inches, either solid or perforated. This lath will not burn or transmit temperatures much in excess of 212°F until the gypsum is completely calcined. The strength of the bond of plaster to gypsum lath is great. It requires a pull of 864 pounds per square foot to separate gypsum plaster from gypsum lath, based on a 2:1 mix of sand and plaster mortar.
There is also a special fire-retardant gypsum lath, called type X. It has a specially formulated core that contains minerals, giving it additional fire protection.
Use only one manufacturer’s materials for a specified job or area. This ensures compatibility. Always strictly follow the manufacturer’s specifications for materials and conditions of application.
Plain gypsum lath plaster base is used in several situations: for applying nails and staples to wood and nailable steel framing; for attaching clips to wood framing, steel studs, and suspended metal grillage; and for attaching screws to metal studs and furring channels. Common sizes include 16 by 48 inches, 3/8 or 1/2 inch thick, and 16 by 96 inches, 3/8 inch thick.
Perforated gypsum lath plaster base is the same as plain gypsum lath except that 3/4 inch round holes are punched through the lath 4 inches on center (OC) in each direction. This gives one 3/4 inch hole for each 16 square inches of lath area. This provides mechanical keys in addition to the natural plaster bond and obtains higher fire ratings. Figure 29 shows back and side views of a completed application.
Figure 29 – Keys formed with perforated gypsum board.
Insulating gypsum lath plaster base is the same as plain gypsum lath, but with bright aluminum foil laminated to the back. This creates an effective vapor barrier at no additional labor cost. In addition, it provides positive insulation when installed with the foil facing a 3/4 inch minimum air space. When insulating gypsum lath plaster is used as a ceiling, and under winter heating conditions, its heat-resistance value is approximately the same as that for 1/2 inch insulation board.
Long lengths of gypsum lath are primarily used for furring the interior side of exterior masonry walls. It is available in sizes 24 inches wide, 3/8 inch thick, and up to 12 feet in length.
Gypsum lath is easily cut by scoring one or both sides with a utility knife. Break the lath along the scored line. Be sure to make neatly fitted cutouts for utility openings, such as plumbing pipes and electrical outlets.
Metal lath is perhaps the most versatile of all plaster bases. Essentially a metal screen, the bond is created by keys formed by plaster forced through the openings. As the plaster hardens, it becomes rigidly interlocked with the metal lath.
Three types of metal lath are commonly used: diamond mesh (expanded metal), expanded rib, and wire mesh (woven wire).
Diamond Mesh– The terms diamond mesh and expanded metal refer to the same type of lath shown in Figure 30. It is manufactured by first cutting staggered slits in a sheet and then expanding or stretching the sheet to form the screen openings. The standard diamond mesh lath has a mesh size of 5/16 by 9/16 inch. Lath is made in sheets of 27 by 96 inches and is packed 10 sheets to a bundle (20 square yards).
Figure 30 – Diamond mesh (expanded metal) lath.
Diamond mesh lath is also made in a large mesh. This is used for stucco work, concrete reinforcement, and support for rock wool and similar insulating materials. Sheet sizes are the same as for the small mesh. The small diamond mesh lath is also made into a self furring lath by forming dimples into the surface that hold the lath approximately 1/4 inch away from the wall surface. This lath may be nailed to smooth concrete or masonry surfaces. It is widely used when replastering old walls and ceilings when the removal of the old plaster is not desired. Another lath form is paper backed where the lath has a waterproof or kraft paper glued to the back of the sheet. The paper acts as a moisture barrier and plaster saver.
Expanded Rib – Expanded rib lath shown in Figure 31 is like diamond mesh lath except that various size ribs are formed in the lath to stiffen it. Ribs run lengthwise of the lath and are made for plastering use in 1/8, 3/8, and 3/4 inch rib height. The sheet sizes are 27 to 96 inches in width, and 5,10, and 12 foot lengths for the 3/4 inch rib lath.
Figure 31 – Expanded rib lath.
Wire Mesh – Woven wire lath, shown in Figure 32, is made of galvanized wire of various gauges woven or twisted together to form either squares or hexagons. It is commonly used as a stucco mesh where it is placed over tar paper on open-stud construction or over various sheathing. 3.7.0 Installation Let’s now look at the basic installation procedures for plaster bases and accessories.
Figure 32 – Woven wire lath.
Gypsum lath is applied horizontally with staggered end joints, as shown in Figure 33.
Figure 33 – Lath joints.
Vertical end joints should be made over the center of studs or joists. Lath joints over openings should not occur at the jamb line. Do not force the boards tightly together; let them butt loosely so the board is not under compression before the plaster is applied. Use small pieces only where necessary. The most common method of attaching the boards has been the lath nail. More recently, though, staples have gained wider use (due mainly to the ready availability of power guns).
The nails used are 1 1/8 inches by 13 gauge, flat headed, blued gypsum lath nails for 3/8 inch thick boards and 1 1/4 inches for 1/2 inch boards. There are also resin coated nails, barbed shaft nails, and screw type nails in use. Staples should be No. 16 U.S. gauge flattened galvanized wire formed with a 7/16 inch wide crown and 7/8 inch legs with divergent points for 3/8 inch lath. For 1/2 inch lath, use 1 inch long staples.
Four nails or staples are used on each support for 16 inch-wide lath and five for 2 footwide lath. Some special fire ratings, however, require five nails or staples per 16 inch board. Five nails or staples are also recommended when the framing members are spaced 24 inches apart.
Start nailing or stapling 1/2 inch from the edges of the board. Nail on the framing members falling on the center of the board first, and then work to either end. This should prevent buckling.
Insulating lath should be installed much the same as gypsum lath except that slightly longer blued nails are used. A special waterproof facing is provided on one type of gypsum board for use as a ceramic tile base when the tile is applied with an adhesive.
All metal lath is installed with the sides and ends lapped over each other. The laps between supports should be securely tied, using 18 gauge tie wire. In general, metal lath is applied with the long length at right angles to the supports. Rib lath is placed with the ribs against the supports and the ribs nested where the lath overlaps. Generally, metal lath and wire lath are lapped at least 1 inch at the ends and 1/2 inch at the sides. Some wire lath manufacturers specify up to 4 1/2 inch end lapping and 2 inch side laps. This is done to mesh the wires and the paper backing.
Lath is either nailed, stapled, or hog tied (heavy wire ring installed with a special gun) to the supports at 6 inch intervals. Use 1 1/2 inch barbed roofing nails with 7/16 inch heads or 1 inch 4 gauge staples for the flat lath on wood supports. For ribbed lath, heavy wire lath, and sheet lath, nails or staples must penetrate the wood 1 3/8 inches for horizontal application and at least 3/4 inch for vertical application. When common nails are used, they must be bent across at least three lath strands.
On channel iron supports, the lath is tied with No. 18 gauge tie wire at 4 inch intervals using lathers’ nippers. For wire lath, the hog tie gun can be used. Lath must be stretched tight as it is applied so that no sags or buckles occur. Start tying or nailing at the center of the sheet and work toward the ends. Rib lath should have ties looped around each rib at all supports, as the main supporting power for rib lath is the rib.
When you install metal laths at both inside and outside corners, bend the lath to form a corner and carry it at least 4 inches in or around the corner. This provides the proper reinforcement for the angle or comer.
A wide variety of metal accessories is produced for use with gypsum and metal lathing. Lathing accessories are usually installed before plastering to form true corners, act as screens for the plasterer, reinforce possible weak points, provide control joints, and provide structural support.
Lathing accessories consist of structural components and miscellaneous accessories. The principal use of structural components is in the construction of hollow partitions. A hollow partition is one containing no building framing members, such as studs and plates. Structural components are lathing accessories that take the place of the missing framing members supporting the lath. These include prefabricated metal studs and floor and ceiling runner tracks. The runner tracks take the place of missing stud top and bottom plates. They usually consist of metal channels. Channels are also used for furring and bracing.
Miscellaneous accessories consist of components attached to the lath at various locations. They serve to define and reinforce comers, provide dividing strips between plaster and the edges of baseboard or other trim, and define plaster edges at unframed openings.
Comer beads fit over gypsum lath outside corners to provide a true, reinforced comer. They are available in either small nose or bullnose types, with flanges of either solid or perforated metal as shown in Figure 34. They are available with expanded metal flanges.
Figure 34 – Perforated flanged corner bead.
Casing beads are similar to comer beads and are used both as finish casings around openings in plaster walls and as screens to obtain true surfaces around doors and windows. They are also used as stops between a plaster surface and another material, such as masonry or wood paneling. Casing beads are available as square sections, modified square sections, and quarter rounds.
Base or parting screens are used to separate plaster from other flush surfaces, such as concrete. Ventilating expansion screen is used on the underside of closed soffits and in protected vertical surfaces for ventilation of enclosed attic spaces. Drip screens act as terminators of exterior Portland cement plaster at concrete foundation walls. They are also used on external horizontal comers of plaster soffits to prevent drip stains on the underside of the soffit. A metal base acts as a flush base at the bottom of a plaster wall. It also serves as a plaster screen.
Because some drying usually takes place in the wood framing members after a structure is completed, some shrinkage is expected. This, in turn, may cause plaster cracks to develop around openings and in the comers. To minimize, if not eliminate, these cracks, use expanded metal lath in key positions over the plaster base material as reinforcements. Strip reinforcement (strips of expanded metal lath) can be used over door and window openings as shown in Figure 35. A 10 to 20 inch strip is placed diagonally across each upper comer of the opening and tacked in place.
Strip reinforcement should also be used under flush ceiling beams as shown in Figure 36 to prevent plaster cracks. On wood drop beams extending below the ceiling line, the metal lath is applied with furring nails to provide space for keying the plaster.
Figure 37 – Plaster reinforcing at corners.
Corner beads of expanded metal lath or of perforated metal as shown in Figure 37 should be installed on all outside comers. They should be applied plumb and level. Each bead acts as a leveling edge when walls are plastered and reinforces the comer against mechanical damage. To minimize plaster cracks, reinforce the inside comers at the juncture of walls and ceilings. Metal lath, or wire fabric, is tacked lightly in place in these corners.
Figure 38 - Control joint.
Control joints as shown in Figure 38 are formed metal strips used to relieve stresses and strains in large plaster areas or at junctures of dissimilar materials on walls and ceilings. Cracks can develop in plaster or stucco from a single cause or a combination of causes, such as foundation settlement, material shrinkage, building movement, and so forth. The control joint minimizes plaster cracking and assures proper plaster thickness. The use of control joints is extremely important when Portland cement plaster is used.
Plastering grounds are strips of wood used as plastering guides or strike off edges and are located around window and door openings and at the base of the walls. Grounds around interior door openings, shown in Figure 39, View A, are full width pieces nailed to the sides over the studs and to the underside of the header. They are 5 1/4 inches wide, which coincides with the standard jamb width for interior walls with a plaster finish. They are removed after the plaster has dried. Narrow strip grounds shown in View B can also be used around interior openings.
Figure 39 – Plaster grounds.
In window and exterior door openings, the frames are normally in place before the plaster is applied. The inside edges of the side and head jambs can, and often do, serve as grounds. The edge of the window might also be used as a ground, or you can use a narrow 7/8 inch thick ground strip nailed to the edge of the 2 by 4 inch sill, as shown in View C. These are normally left in place and covered by the casing.
A similar narrow ground or screen is used at the bottom of the wall to control the thickness of the gypsum plaster and to provide an even surface for the baseboard and molding. This screen is also left in place after the plaster has been applied.
Some plaster comes ready mixed, requiring only the addition of enough water to attain minimum required workability. For job mixing, tables are available giving recommended ingredient proportions for gypsum, lime, lime Portland cement, and Portland cement plaster for base coats on lath or on various types of concrete or masonry surfaces, and for finish coats of various types. In this course, we’ll cover recommended proportions for only the more common types of plastering situations.
In the following discussion, one part of cementitious material means 100 pounds (one sack) of gypsum, 100 pounds (two sacks) of hydrated lime, 1 cubic foot of lime putty, or 94 pounds (one sack) of Portland cement. One part of aggregate means 100 pounds of sand or 1 cubic foot of vermiculite or perlite.
Vermiculite and perlite are not used with lime plaster.
While aggregate parts given for gypsum or Portland cement plaster may be presumed to refer to either sand or vermiculite/perlite, the aggregate part given for lime plaster means sand only.
Base Coat Proportions – Two-coat plasterwork consists of a single base coat and a finish coat. Three-coat plasterwork consists of two base coats (the scratch coat and the brown coat) and a finish coat.
Portland cement plaster cannot be applied to a gypsum base. Lime plaster can, but in practice, only gypsum plaster is applied to gypsum lath as a base coat. For two coat work on gypsum lath, the recommended base coat proportions for gypsum plaster are 1:2.5. For two-coat work on a masonry (either monolithic concrete or masonry) base, the recommended base coat proportions are shown in Table 1. Also shown in Table 1 are proportions for three-coat work on a masonry base and proportions for work on metal lath.
Table 1 – Base Coat Proportions for Different Types of Work.
For three-coat work on gypsum lath, the recommended base coat proportions for gypsum plaster are shown in Table 2.
Table 2 – Recommended Base Coat Proportions for Gypsum Plaster.
Finish Coat Proportions – A lime finish can be applied over a lime, gypsum, or Portland cement base coat. Other finishes should be applied only to base coats containing the same cementitious material. A gypsum vermiculite finish should be applied only to a gypsum vermiculite base coat.
Finish coat proportions vary according to whether the surface is to be finished with a trowel or with a float. The trowel attains a smooth finish; the float produces a textured finish.
For a trowel finish coat using gypsum plaster, the recommended proportions are 200 pounds of hydrated lime or 5 cubic feet of lime putty to 100 pounds of gypsum gauging plaster. For a trowel finish coat using lime Keene’s cement plaster, the recommended proportions for a medium hard finish are 50 pounds of hydrated lime or 100 pounds of lime putty to 100 pounds of Keene’s cement. For a hard finish, the recommended proportions are 25 pounds of hydrated lime or 50 pounds of lime putty to 100 pounds of Keene’s cement.
For a trowel finish coat using lime Portland cement plaster, the recommended proportions are 200 pounds of hydrated lime or 5 cubic feet of lime putty to 94 pounds of Portland cement.
For a finish coat using Portland cement sand plaster, the recommended proportions are 300 pounds of sand to 94 pounds of Portland cement. This plaster may be either troweled or floated. Hydrated lime up to 10 percent by weight of the Portland cement, or lime putty up to 24 percent of the volume of the Portland cement, may be added as a plasticizer.
For a trowel finish coat using gypsum gauging or gypsum neat plaster and vermiculite aggregate, the recommended proportions are 1 cubic foot of vermiculite to 100 pounds of plaster.
The total volume of plaster required for a job is the product of the thickness of the plaster times the net area to be covered. Plaster specifications state a minimum thickness, which you must not go under. Also, you should exceed the specs as little as possible due to the increased tendency of plaster to crack with increased thickness.
The two basic operations in mixing plaster are determining the correct proportions and the actual mixing methods used.
Proportions – The proper proportions of the raw ingredients required for any plastering job are found in the job specifications. The specs also list the types of materials to use and the type of finish required for each area. Hardness and durability of the plaster surface depend upon how accurately you follow the correct proportions. Too much water gives you a fluid plaster that is hard to apply. It also causes small holes to develop in the finish mortar coat. Too much aggregate in the mix, without sufficient binder to unite the mixture, causes aggregate particles to crumble off.
Without exception, consult the specifications prior to the commencement of any plaster job.
Mixing Methods – As a Builder, you will be mixing plaster either by hand or by using a machine.
Hand Mixing – To hand mix plaster, you will need a flat, shallow mixing box and a hoe. The hoe usually has one or more holes in the blade. Mixed plaster is transferred from the mixing box to a mortar board, similar to that used in bricklaying. Personnel applying the plaster pick it up from the mortarboard.
In hand mixing, first place the dry ingredients in a mixing box and thoroughly mix until a uniform color is obtained. After thoroughly blending the dry ingredients, you then cone the pile and add water to the mix. Begin mixing by pulling the dry material into the water with short strokes. Mixing is continued until the materials have been thoroughly blended and proper consistency has been attained. With experience, you acquire a feel for proper consistency. Mixing should not be continued for more than 10 to 15 minutes after the materials have been thoroughly blended. Excessive agitation may hasten the rate of solution of the cementitious material and reduce initial set time.
Finish coat lime plaster is usually hand mixed on a 5 by 5 foot mortar board called a finishing board. Hydrated lime is first converted to lime putty by soaking in an equal amount of water for 16 hours. In mixing the plaster, you first form the lime putty into a ring on the finishing board. Next, pour water into the ring and sift the gypsum or Keene’s cement into the water to avoid lumping. Last, allow the mix to stand for 1 minute, and then thoroughly blend the materials. If sand is used, it is added last and mixed in.
Machine Mixing – For a quicker, more thorough mix, use a plaster mixing machine. A typical plaster mixing machine, shown in Figure 40, consists primarily of a metal drum containing mixing blades mounted on a chassis equipped with wheels for road towing. Sizes range from 3 1/2 to 10 cubic feet and can be powered by an electric or a gasoline motor. Mixing takes place either by rotation of the drum or by rotation of the blades inside the drum. Tilt the drum to discharge plaster into a wheelbarrow or other receptacle.
Figure 40 – Plaster mixing machine.
When using a plaster mixer, add the water first, and then add about half the sand. Next, add the cement and any admixture desired. Last, add the rest of the sand.
Mix until the batch is uniform and has the proper consistency; 3 to 4 minutes is usually sufficient. Note that excessive agitation of mortar speeds up the setting time. Most mixers operate at top capacity when the mortar is about 2 inches, at most, above the blades. When the mixer is charged higher than this, proper mixing fails to take place. Instead of blending the materials, the mixer simply folds the material over and over, resulting in excessively dry mix on top and too wet mix underneath, a bad mix. Eliminate this situation by not overloading the machine.
Workers handling cement or lime bags should wear recommended personnel protective gear. Always practice personal cleanliness. Never wear clothing that is hard and stiff with cement. Such clothing irritates the skin and may cause serious infection. Report any susceptibility of skin to cement and lime bums to your supervisor immediately.
Do not pile bags of cement or lime more than 10 bags high on a pallet except when stored in bins or enclosures built for such purposes. Place the bags around the outside of the pallet with the tops of the bags facing the center. To prevent piled bags from falling outward, crosspile the first five tiers of bags each way from any comer, and make a setback starting with the sixth tier. If you have to pile above the 10th tier, make another setback. The back tier, when not resting against a wall of sufficient strength to withstand the pressure, should also be set back one bag every five tiers.
During unpiling, the entire top of the pile should be kept level and the setbacks maintained for every five tiers.
Lime and cement must be stored in a dry place to help prevent the lime from crumbling and the cement from hydrating before it is used.
A plaster layer must have uniform thickness to attain complete structural integrity. Also, a plane plaster surface must be flat enough to appear flat to the eye and receive surface- applied materials, such as casings and other trim, without the appearance of noticeable spaces. Specified flatness tolerance is usually 1/8 inch in 10 feet.
Plastering requires the use of a number of tools, some specialized, including trowels, hawks, floats, straight and feather edges, darbys, scarifiers, and plastering machines.
Steel trowels are used to apply, spread, and smooth plaster. The shape and size of the trowel blade are determined by the purpose for which the tool is used and the manner of using it.
Figure 41 – Plastering trowels.
The four common types of plastering trowels are shown in Figure 41. The rectangular trowel, with a blade approximately 4 1/2 inches wide by 11 inches long, serves as the principal conveyor and manipulator of plaster. The pointing trowel, 2 inches wide and about 10 inches long, is used in places where the rectangular trowel does not fit. The margin trowel is a smaller trowel, similar to the pointing trowel, but with a square, rather than a pointed, end. The angle trowel is used for finishing comer angles formed by adjoining right angle plaster surfaces.
Figure 42 – Plastering hawk.
The hawk, shown in Figure 42, is a square, lightweight sheet metal platform with a vertical central handle, used for carrying mortar from the mortar board to the place where it is to be applied. The plaster is then removed from the hawk with the trowel. The size of a hawk varies from a 10 to a 14 inch square. A hawk can be made in the field from many different available materials.
A float is glided over the surface of the plaster to fill voids and hollows, to level bumps left by previous operations, and to impart a texture to the surface. The most common types of float are shown in Figure 43. The wood float has a wood blade 4 to 5 inches wide and about 10 inches long. The angle float has a stainless steel or aluminum blade. The sponge float is faced with foam rubber or plastic, intended to attain a certain surface texture.
Figure 43 – Plastering floats.
In addition to these floats, other floats are also used in plasterwork. A carpet float is similar to a sponge float, but is faced with a layer of carpet material. A cork float is faced with cork.
The rod or straightedge consists of a wood or lightweight metal blade 6 inches wide and 4 to 8 feet long, as shown in Figure 44. This is the first tool used in leveling and straightening applied plaster between the grounds. A wood rod has a slot for a handle cut near the center of the blade. A metal rod usually has a shaped handle running the length of the blade.
Figure 44 – Straightedge and featheredge.
The featheredge, shown in Figure 44, is similar to the rod except that the blade tapers to a sharp edge. It is used to cut in inside corners and to shape sharp, straight lines at outside comers where walls intersect.
The darby, shown in Figure 45, is, in effect, a float with an extra long (3 1/2 to 4 foot) blade, equipped with handles for two handed manipulation. It is used for further straightening of the base coat, after rodding is completed, to level plaster screens and to level finish coats. The blade of the darby is held nearly flat against the plaster surface, and in such a way that the line of the edge makes an angle 45° with the line of direction of the stroke.
Figure 45 – Darby.
When a plaster surface is being leveled, the leveling tool must move over the plaster smoothly. If the surface is too dry, lubrication must be provided by moistening. In base coat operations, dash or brush on water with a water-carrying brush called a browning brush. This is a fine bristled brush about 4 to 5 inches wide and 2 inches thick, with bristles about 6 inches long. For finish coat operations, a finishing brush with softer, more pliable bristles is used.
The scarifier, shown in Figure 46, is a raking tool that leaves furrows approximately 1/8 inch deep, 1/8 inch wide, and 1/2 inch to 3/4 inch apart. The furrows are intended to improve the bond between the scratch coat and the brown coat.
Figure 46 – Scarifier.
There are two types of plastering machines, wet mix and dry mix. The wet mix pump type carries mixed plaster from the mixing machine to a hose nozzle. The dry mix machine carries dry ingredients to a mixing nozzle where water under pressure combines with the mix and provides spraying force. Most plastering machines are of the wet mix pump variety.
A wet mix pump may be of the worm drive, piston pump, or hand hopper type. In a worm drive machine, mixed plaster is fed into a hopper and forced through the hose to the nozzle by the screw action of a rotor and stator assembly in the neck of the **42 machine. A machine of this type has a hopper capacity of from 3 to 5 cubic feet and can deliver from 0.5 to 2 cubic feet of plaster per minute. On a piston pump machine, a hydraulic, air-operated, or mechanically-operated piston supplies the force for moving the wet plaster. On a hand hopper machine, the dry ingredients are placed in a handheld hopper just above the nozzle. Hopper capacity is usually around 1/10 cubic foot. These machines are mainly used for applying finish plaster.
Machine application reduces the use of the hawk and trowel in initial plaster application. However, the use of straightening and finishing hand tools remains about the same for machine applied plaster.
A typical plastering crew for hand application consists of a crew leader, two to four plasterers, and two to four tenders. The plasterers, under the crew leader’s supervision, set all levels and lines and apply and finish the plaster. The tenders mix the plaster, deliver it to the plasterers, construct scaffolds, handle materials, and do cleanup tasks.
For a machine application, a typical crew consists of a nozzle operator who applies the material, two or three plasterers leveling and finishing, and two to three tenders.
Lack of uniformity in the thickness of a plaster coat detracts from the structural performance of the plaster, and the thinner the coat, the smaller the permissible variation from uniformity. Specifications usually require that plaster be finished true and even, within 1/8 inch tolerance in 10 feet, without waves, cracks, or imperfections. The standard of 1/8 inch appears to be the closest practical tolerance to which a plasterer can work by the methods commonly in use.
The importance of adhering to the recommended minimum thickness for the plaster cannot be overstressed. A plaster wall becomes more rigid as thickness over the recommended minimum increases. As a result, the tendency to crack increases as thickness increases. Tests have shown that a reduction of thickness from a recommended minimum of 1/2 inch to 3/8 inch, with certain plasters, decreases resistance by as much as 60 percent, while reduction to 1/4 inch decreases it as much as 82 percent.
The sequence of operations in three-coat gypsum plastering is as follows:
The steps for lime base coat work are similar to those for gypsum work except that, for lime, an additional floating is required the day after the brown coat is applied. This extra floating is required to increase the density of the slab and to fill in any cracks that may have developed because of shrinkage of the plaster. A wood float with one or two nails protruding 1/8 inch from the sole, called a devil’s float, is used for this purpose.
Portland cement plaster is actually cement mortar. It is usually applied in three coats, the steps being the same as those described for gypsum plaster. Minimum recommended thicknesses are usually 3/8 inch for the scratch coat and brown coat, and 1/8 inch for the finish coat.
Portland cement plaster should be moist cured, similar to concrete. The best procedure is fog spray curing. The scratch coat and the brown coat should both be fog spray cured for 48 hours. The finish coat should not be applied for at least 7 days after the brown coat. It should also be spray cured for 48 hours.
Interior plaster can be finished by troweling, floating, or spraying. Troweling makes a smooth finish; floating or spraying makes a finish of a desired surface texture.
Finish plaster made of gypsum gauging plaster and lime putty, called white coat or putty coat, is the most widely used material for smooth finish coats. A putty coat is usually applied by a team of two or more persons. The steps are as follows:
The sequence of steps for trowel finishes for other types of finish plasters is about the same. Gypsum finish plaster requires less troweling than white coat plaster. Regular Keene’s cement requires longer troweling, but quick setting Keene’s cement requires less. Preliminary finishing of Portland cement sand is done with a wood float, after which the steel trowel is used. To avoid excessive drawing of fine aggregates to the surface, delay troweling of the Portland cement sand as long as possible. For the same reason, the surface must not be troweled too long.
The steps in float finishing are about the same as those described for trowel finishing, except that the final finish is obtained with the float. A surface is usually floated twice, a rough floating with a wooden float first, then a final floating with a rubber or carpet float. With one hand the plasterer applies water with the brush, while moving the float in the other hand in a circular motion immediately behind the brush.
Some special interior finish textures are obtained by methods other than or in addition to floating. A few of these are listed below.
Test your Knowledge
3. For plaster application, what must be installed between structural members to form a continuous surface?
- A. Plaster planes
- B. Insulation
- C. Lath
- D. Fire blocking
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Stucco is the term applied to plaster whenever it is applied to the exterior of a building or structure. Stucco can be applied over wood frames or masonry structures. A stucco finish lends warmth and interest to projects.
Stucco is a combination of cement or masonry cement, sand and water, and frequently a plasticizing material. Color pigments are often used in the finish coat, which is usually a factory-prepared mix. The end product has all the desirable properties of concrete. Stucco is hard, strong, fire-resistant, and weather-resistant; it does not deteriorate after repeated wetting and drying, resists rot and fungus, and retains colors.
The material used in a stucco mix should be free of contaminants and unsound particles. Type I normal Portland cement is generally used for stucco, although type II, type III, and air entraining may be used. The plasticizing material added to the mix is hydrated lime. Mixing water must be potable. The aggregate used in cement stucco can greatly affect the quality and performance of the finished product. It should be well graded, clean, and free from loam, clay, or vegetable matter, which can prevent the cement paste from properly binding the aggregate particles together. Follow the project specifications as to the type of cement, lime, and aggregate to be used.
Metal reinforcement should be used whenever stucco is applied on wood frame, steel frame, flashing, masonry, or any surface not providing a good bond. Stucco may be applied directly on masonry. The rough floated base coat is approximately 3/8 inch thick. The finish coat is approximately 1/4 inch thick. Both are shown in Figure 47 applied to a masonry surface.
Figure 47 – Masonry with two-coat work directly applied.
On open frame construction, shown in Figure 48, nails are driven one half their length into the wood. Spacing should be 5 to 6 inches OC from the bottom. Nails should be placed at all corners and openings throughout the entire structure on the exterior. The next step is to place wire on the nails. This is called installing the line wire. Next, a layer of waterproof paper is applied over the line wire. Laps should be 3 to 4 inches and nailed with roofing nails. Install wire mesh (stucco netting), which is used as the reinforcement for the stucco.
Figure 48 – Open frame construction.
Furring nails, shown in Figure 49, are used to hold the wire away from the paper to a thickness of three eighths of an inch. Stucco or sheathed frame construction is the same as open frame except no line wire is required. The open and sheathed frame construction requires three coats of 3/8 inch scratch coat horizontally scored or scratched, a 3/8 inch brown coat, and a 1/8 inch finish coat.
Figure 49 – Several types of furring nails.
Stucco is usually applied in three coats. The first coat is the scratch coat, the second the brown coat, and the final coat the finish coat. On masonry where no reinforcement is used, two coats may be sufficient. Start at the top and work down the wall. This prevents mortar from falling on the completed work. The first, or scratch, coat should be pushed through the mesh to ensure the metal reinforcement is completely embedded **47 for mechanical bond. The second, or brown, coat should be applied as soon as the scratch coat has set up enough to carry the weight of both coats, usually 4 or 5 hours. The brown coat should be moist cured for about 48 hours and then allowed to dry for about 5 days. Just before the application of the finish coat, the brown coat should be uniformly dampened. The third, or finish, coat is frequently pigmented to obtain decorative colors. Although the colors may be job-mixed, a factory-prepared mix is recommended. The finish coat may be applied by hand or machine. Stucco finishes are available in a variety of textures, patterns, and colors.
Before the various coats of stucco can be applied, the surfaces have to be prepared. Roughen the surfaces of masonry units enough to provide good mechanical key, and clean off paint, oil, dust, soot, or any other material that may prevent a tight bond. Joints may be struck off flush or slightly raked. Old walls softened and disintegrated by weather action, surfaces that cannot be cleaned thoroughly, such as painted brickwork, and all masonry chimneys should be covered with galvanized metal reinforcement before applying the stucco. When masonry surfaces are not rough enough to provide good mechanical key, one or more of the following actions may be taken:
Add muriatic acid to the water; never add water to the acid.
When your crew members are using muriatic acid, make sure they wear goggles, rubber gloves, and other protective clothing and equipment.
Figure 50 – Power driven roughing machine.
When the masonry surface is not rough enough to ensure an adequate bond for a trowel-applied scratch coat, use the dash method. Acid treated surfaces usually require a dashed scratch coat. Dashing on the scratch coat aids in getting a good bond by excluding air that might get trapped behind a trowel applied coat. Apply the dash coat with a fiber brush or whisk broom, using a strong whipping motion at right angles to the wall. A cement gun or other machine that can apply the dash coat with considerable force also produces a suitable bond. Keep the dash coat damp for at least 2 days immediately following its application and then allow it to dry.
Protect the finish coat against exposure to sun and wind for at least 6 days after application. During this time, keep the stucco moist by frequent fog spraying.
Mixing procedures for stucco are similar to those for plaster. Three things you need to consider before mixing begins are the type of material you are going to use, the backing to which the material will be applied, and the method used to mix the material (hand or machine). As with plaster, addition of too much of one raw ingredient or the deletion of a raw material gives you a bad mix. Prevent this by using only the required amount of ingredients in the specified mix.
Stucco can be applied by hand or machine. Machine application allows application of material over a large area without joinings. Joinings are a problem for hand applied finishes. To apply stucco, begin at the top of the wall and work down. Make sure the crew has sufficient personnel to finish the total wall surface without joinings, such as laps or interruptions.
The curing of stucco depends on the surface to which it is applied, the thickness of the material, and the weather. Admixtures can be used to increase workability, prevent freezing, and to waterproof the mortar. Using high early cement reduces the curing time required for the cement to reach its initial strength to 3 days instead of 7. Air entraining cement is used to resist freezing action.
There are times when the finish you get is not what you expected. Some of the most common reasons for discoloration and stains are listed below.
Test your Knowledge
4. A brown coat of stucco should be moist cured for how many hours?
- A. 8
- B. 16
- C. 24
- D. 48
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Ceramic tile is generally used to partially or entirely cover interior walls, such as those in bathrooms, showers, galleys, and corridors. The tile is made of clay, pressed into shape, and baked in an oven.
Ceramic tile is used extensively where sanitation, stain resistance, ease in cleaning, and low maintenance are desired. Ceramic tiles are commonly used for walls and floors in bathrooms, laundry rooms, showers, kitchens, laboratories, swimming pools, and locker rooms. The tremendous range of colors, patterns, and designs available in ceramic tile even includes three-dimensional sculptured tiles. Extensive use has been made of ceramic tile for decorative effects throughout buildings, both inside and outside.
Tile is usually classified by exposure (interior or exterior) and location (walls or floors), although many tiles may be used in all locations. Since exterior tile must be frostproof, the tiles are kiln fired to a point where they have a very low absorption. Tiles vary considerably in quality among manufacturers. This may affect their use in various exposures and locations.
Tile is available in square sizes including 4 1/4 by 4 1/4, 6 by 6, 3 by 3, and 1 3/8 by 1 3/8 inches. Rectangular sizes available include 8 1/2 by 4 1/4, 6 by 4 1/4, and 1 3/8 by 4 1/4 inches. Tile often comes mounted into sheets, usually between 1 and 2 square feet, with some type of backing on the sheet or between the tiles to hold them together.
Tiles with less than 6 square inches of face area and about 1/4 inch thick are called ceramic mosaics. Ceramic mosaic tile sizes range from 3/8 by 3/8 inch to about 2 by 2 inches. They are available from the manufactures in both sheet and roll form. Often large tile is scored by the manufacturer to resemble small tiles.
Tile finishes include glazed, unglazed, textured (matte) glazed porcelain, and abrasive. Glazed and matte glazed finishes may be used for light-duty floors but should not be used in areas of heavy traffic where the glazed surface may be worn away. Glazed ceramic wall tiles usually have a natural clay body which is non=vitreous, 7 to 9 percent absorption, with a vitreous glaze fused to the face of the tile. This type of tile is not recommended for exterior use. Glazed tile should never be cleaned with acid, which mars the finish. Use only soap and water. Unglazed ceramic mosaics have dense, non-vitreous bodies uniformly distributed through the tile. Certain glazed mosaics are recommended for interior use only, others for wall use only. Porcelain tiles have a smoother surface than mosaics and are denser, with an impervious body of less than one half of 1 percent absorption. This type of tile may be used throughout the interior and exterior of a building. An abrasive finish is available as an aggregate embedded in the surface or an irregular surface texture.
Tiles are available with self-spacing lugs, square edges, and cushioned edges which are slightly rounded, as shown in Figure 51. The lugs assure easy setting and uniform joints. The edges available vary with the size of the tile and the manufacturer.
Figure 51 – Tile edges.
Margins, corners, and base lines are finished with trimmers of various shapes, as shown in Figure 51. A complete line of shaped ceramic trim is available from manufacturers. Other accessories include towel bars, shelf supports, paper holders, grab rails, soap holders, tumbler holders, and combination toothbrush and tumbler holders, to list a few of the more popular units.
Figure 52 – Trimmer shapes.
The resistance of ceramic tile to traffic depends primarily on base and bonding material rigidity, grout strength, hardness, and the accurate leveling and smoothness of the individual tiles in the installation. The four basic installation methods are cement mortar (the only thick bed method), dry set mortar, epoxy mortar, and organic adhesives (mastic).
Cement mortar for setting ceramic tiles is composed of a mixture of Portland cement and sand. The mix proportions for floors vary from 1:3 to 1:6 by volume. For walls, a Portland cement, sand, and hydrated lime mix vary from 1:3:1 to 1:5 1/2:1. These proportion ratios are dictated by the project specifications. The mortar is placed on the surface 3/4 to 1 inch thick on walls and 3/4 inch to 1 1/4 inches thick on floors. A neat cement bond coat is applied over it while the cement mortar is fresh and plastic. After soaking in water for at least 30 minutes, the tiles are installed over the neat cement bond coat. This type of installation, with its thick mortar bed, permits wall and floor surfaces to be sloped. This installation provides bond strength of 100 to 200 pounds per square inch. A waterproof backing is sometimes required, and the mortar must be damp cured.
Dry-set mortar is a thin bed mortar of premixed Portland cement, sand, and admixtures that control the setting (hardening) time of the mortar. It may be used over concrete, block, brick, cellular foamed glass, gypsum wallboard, and unpainted dry cement plaster, as well as other surfaces. A sealer coat is often required when the base is gypsum plaster. It is not recommended for use over wood or wood products. Dry-set mortar can be applied in one layer 3/32 inch thick, and it provides bond strength of 500 pounds per square inch. This method has excellent water and impact resistance and may be used on exteriors. The tiles do not have to be presoaked, but the mortar must be damp cured.
Epoxy mortar can be applied in a bed as thin as 1/8 inch. When the epoxy resin and hardener are mixed on the job, the resulting mixture hardens into an extremely strong, dense setting bed. Pot life, once the parts are mixed, is about 1 hour if the temperature is 82°F or higher. This mortar has excellent resistance to the corrosive conditions often encountered in industrial and commercial installations. It may be applied over bases of wood, plywood, concrete, or masonry. This type of mortar is non-shrinking and nonporous. Bond strength of over 1,000 pounds per square inch is obtained with this installation method.
Organic adhesives (mastics) are applied in a thin layer with a notched trowel. They are solvent base, rubber material. Porous materials should be primed before mastic is applied to prevent some of the plasticizers and oils from soaking into the backing. Suitable surfaces include wood, concrete, masonry, gypsum wallboard, and plaster. The bond strength available varies considerably among manufacturers, but the average is about 100 pounds per square inch.
The joints between the tiles must be filled with a grout selected to meet the tile requirements and exposure. Tile grouts may be Portland cement base, epoxy base, furans, or latex.
Cement grout consists of Portland cement and admixtures. This is better in terms of waterproofing, uniform color, whiteness, shrink resistance, and fine texture than plain cement. It may be colored and used in all areas subject to ordinary use. When the grout is placed, the tiles should be wet. Moisture is required for proper curing.
Drywall grout has the same characteristics as dry-set mortar and is suitable for areas of ordinary use. Tiles to be set in drywall grout do not require wetting except during very dry conditions.
Epoxy grout consists of an epoxy resin and hardener. It produces a joint that is stain-proof, resistant to chemicals, hard, smooth, impermeable, and easy to clean. It is used extensively in counters that must be kept sanitary for foods and chemicals. It has the same basic characteristics as epoxy mortars.
Furan resin grout is used in industrial areas requiring high resistance to acids and weak alkalies. Special installation techniques are required with this type of grouting.
Latex grout is used for a more flexible and less permeable finish than cement grout. It is made by introducing a latex additive into the Portland cement grout mix.
A selection of special tools, shown in Figures 13-53 through 13-56, should be available when doing tile installation work.
A primary tool is a notched trowel with the notches of the depth recommended by the adhesive manufacturers. A trowel notched on one side and smooth on the other is preferred. Different sized trowels are available.
Figure 53 – Tile-setting trowels.
A tile cutter is the most efficient tool for cutting ceramic tile. The scribe on the cutter has a tungsten carbide tip. A glass cutter can be used but quickly dulls.
Figure 54 – Tile cutter.
Use tile nippers when trimming irregular shapes. Nip off very small pieces of the tile you are cutting. Attempting to take big chunks at one time can crack the tile.
Figure 55 – Tile nippers.
A rubber-surfaced trowel is used to force grout into the joints of the tile.
Figure 56 – Rubber-surfaced trowel.
There are three primary steps in tile installation: applying a mortar bed, applying adhesive, and setting tiles in place.
Before applying a mortar bed to a wall with wooden studs, you first tack a layer of waterproof paper to the studs. Then nail metal lath over the paper. The first coat of mortar applied to a wall for setting tiles is a scratch coat; the second is a float, leveling, or brown coat.
A scratch coat for application as a foundation coat must be at least 1/4 inch thick and composed of 1 part cement to 3 parts sand, with the addition of 10 percent hydrated lime by volume of the cement used. While still plastic, the scratch coat is deeply scored or scratched and cross scratched. Keep the scratch coat protected and reasonably moist during the hydration period. All mortar for scratch and float coats should be used within 1 hour after mixing. Do not re-temper partially hardened mortar. Apply the scratch coat not more than 48 hours or less than 24 hours before setting the tile.
The float coat should be composed of 1 part cement, 1 part hydrated lime, and 3 1/2 parts sand. It should be brought flush with screens or temporary guide strips, placed to give a true and even surface at the proper distance from the finished face of the tile.
Wall tiles should be thoroughly soaked for a minimum of 30 minutes in clean water before being set. Set tiles by troweling a skim coat of neat Portland cement mortar on the float coat, or applying a skim coat to the back of each tile unit and immediately floating the tiles into place. Joints must be straight, level, perpendicular, of even width, and not exceeding 1/16 inch. Wainscots are built of full courses. These may extend to a greater or lesser height, but in no case more than 1 1/2 inch from the specified or figured height. Vertical joints must be maintained plumb for the entire height of the tile work.
All joints in wall tile should be grouted full with a plastic mix of neat white cement or commercial tile grout immediately after a suitable area of the tile has been set. Tool the joints slightly concave, cut off and wipe excess mortar from the face of tiles. Any spaces, crevices, cracks, or depressions in the mortar joints after the grout has been cleaned from the surface should be roughened at once and filled to the line of the cushioned edge, if applicable, before the mortar begins to harden. Tile bases or coves should be solidly backed with mortar. Make all joints between wall tiles and plumbing or other built-up fixtures with a light-colored caulking compound. Immediately after the grout has set, apply a protective coat of noncorrosive soap or other approved protection to the tile wall surfaces.
The installation of wall tile over existing and patched or new plaster surfaces in an existing building is completed as previously described, except that an adhesive is used as the bonding agent. Where wall tile is to be installed in areas subject to intermittent or continual wetting, prime the wall areas with adhesive following the manufacturer’s recommendations.
Wall tiles may be installed either by floating or buttering the adhesive. In floating, apply the adhesive uniformly over the prepared wall surface using quantities recommended by the manufacturer. Use a notched trowel held at the proper angle to spread adhesive to the required uniform thickness. Touch up thin or bare spots with an additional coating of adhesive. The area coated at one time should not be any larger than that recommended by the manufacturer. In the buttering method, daub the adhesive on the back of each tile. Use enough so that, when compressed, the adhesive forms a coating not less than 1/16 inch thick over 60 percent of the back of each tile.
The key to a professional looking ceramic tile job is to start working with a squared off area. Most rooms do not have perfectly square comers. As a result, the first step is to mark off a square area in such a way that fractional tiles at the comers (edges) are approximately the same size. Begin by finding the lowest point of the wall you are tiling. From this corner draw a horizontal line one full tile height above the low point and extend this line level across the entire width of the room. Refer to the bathroom wall example in Figure 57 as you study the following steps:
Figure 57 – Steps used for squaring a wall.
Figure 58 – Layout for installing ceramic wall tile.
Another method for figuring fractional tile (edges) is to employ the half tile rule. The stick method is good for short walls, but the half tile rule is needed for long walls. Take the number of full size tiles required for one course, multiply this by the tile size, subtract this answer from the wall length in inches, add one full tile size and divide by 2. The result is the size of end tiles.
After determining fractional tiles, use a piece of scrap wood from 36 inches to 48 inches in length to mark up a tile-measuring stick, as shown in Figure 58, View A. Mark off a series of lines equal to the width of a tile. Lay this stick on the wall and shift it back and forth to determine the starting point for laying the tiles. Make sure the fractional tiles at the end of each row are of equal widths, as shown in Figure 58, View B.
Use a level to establish a line perpendicular to the horizontal starting line, as shown in Figure 59, View C. At both ends of the horizontal line, draw vertical lines to form the squared off area. To make the tile application easier, you can fasten battens to the wall on the outside of the drawn lines.
Use a trowel to spread the mastic over an approximately 3 by 3 foot area of the wall. Use the notched side to form ridges in the mastic, pressing hard against the surface so that the ridges are the same height as the notches on the tool. Allow the mastic to set for 24 hours before applying grout. Follow the manufacturer’s mixing instructions closely and use a rubber-surfaced trowel to spread the grout over the tile surface. Work the trowel in an arc, holding it at a slight angle so that grout is forced into the spaces between the tiles.
Start tiling at either of the vertical lines and tile half the wall at a time, working in horizontal rows. Press each tile into the mastic, but do not slide them; the mastic may be forced up the edges onto the tile surface. After each course of tile is applied, check with the level before spreading more mastic. If a line is crooked, remove all tiles in that line and apply fresh ones. Do not use the removed tiles until the mastic has been cleaned off. Finish tiling the main area before fitting edge tiles.
When the grout begins to dry, wipe the excess from the tiles with a damp rag. After the grout is thoroughly dry, rinse the wall and wipe it with a clean towel.
Non-staining caulking compound should be used at all joints between built in fixtures and tile work and at the top of ceramic tile bases to ensure complete waterproofing. Inside corners should be caulked before a comer bead is applied.
Promptly replace cracked and broken tiles. This protects the edges of adjacent tiles and helps maintain waterproofing and appearance. Timely pointing of displaced joint material and spalled areas in joints is necessary to keep tiles in place.
A new tile surface should be cleaned according to the tile manufacturer’s recommendations to avoid damage to the glazed surfaces.
Test your Knowledge
5. Ceramic tile is normally divided into what two classifications?
- A. Interior and exterior
- B. Exposure and location
- C. Wall and floor
- D. Interior and floor
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Suspended acoustical ceiling systems can be installed to lower a ceiling, finish off exposed joints, cover damaged plaster, or make any room quieter and brighter. The majority of the systems available are primarily designed for acoustical control. Many manufacturers offer systems that integrate the functions of lighting, air distribution, fire protection, and acoustical control. Individual characteristics of acoustical tiles, including sound absorption coefficients, noise reduction coefficients, light reflection values, flame resistance, and architectural applications, are available from the manufacturer.
Tiles are available in 12 to 30 inch widths, 12 to 60 inch lengths, and 3/16 to 3/4 inch thicknesses. The larger sizes are referred to as panels. The most commonly used panels in suspended ceiling systems are the standard 2 by 2 foot and 2 by 4 foot acoustic panels composed of mineral or cellulose fibers.
It is beyond the scope of this course to acquaint you with each of the suspended acoustical ceiling systems in use today. Just as the components of these systems vary according to manufacturers, so do the procedures involved in their installation. With this in mind, the following discussion is designed to acquaint you with the principles involved in the installation of a typical suspended acoustical ceiling system.
The success of a suspended ceiling project, as with any other construction project, is as dependent on planning as it is on construction methods and procedures. Planning in this case involves the selection of a grid system, either steel or aluminum; the selection and layout of a grid pattern; and the determination of material requirements.
Figure 59 shows the major components of a steel and aluminum ceiling grid system used for the 2 by 2 foot or 2 by 4 foot grid patterns shown in Figure 60.
Figure 59 – Ceiling grid system components.
Figure 60 – Grid layout for main tees.
The layout of a grid pattern and the material requirements are based on the ceiling measurements and the length and width of the room at the new ceiling height. If the ceiling length or width is not divisible by 2 (that is, 2 feet), increase those dimensions to the next higher dimension divisible by 2. For example, if a ceiling measures 13 feet 7 inches by 10 feet 4 inches, the dimensions should be increased to 14 by 12 feet for material and layout purposes. Next, draw a layout on graph paper. Make sure the main tees run perpendicular to the joists. Position the main tees on your drawing so the border panels at room edges are equal and as large as possible. Try several layouts to see which looks best with the main tees. Draw in cross tees so the border panels at the room ends are equal and as large as possible. Try several combinations to determine the best. For 2 by 4 foot patterns, space cross tees 4 feet apart. For 2 by 2 foot patterns, space cross tees 2 feet apart. For smaller areas, the 2 by 2 foot pattern is recommended.
As indicated in Figure 59, wall angles and main tees come in 12 foot pieces. Using the perimeter of a room at suspended ceiling height, you can determine the number of pieces of wall angle by dividing the perimeter by 12 and adding 1 additional piece for any fraction. Determine the number of 12-foot main tees and 2-foot or 4-foot cross tees by counting them on the grid pattern layout. In determining the number of 2-foot or 4-foot cross tees for border panels, you must remember that no more than 2 border tees can be cut from one cross tee.
The tools normally used to install a grid system include a hammer, chalk or pencil, pliers, tape measure, screwdriver, hacksaw, knife, and tin snips. With these, you begin by installing the wall angles, then the suspension wires, followed by the main tees, cross tees, and acoustical panels.
The first step is to install the wall angles at the new ceiling height. This can be as close as 2 inches below the existing ceiling. Begin by marking a line around the entire room to indicate the wall angle height and to serve as a level reference. Mark continuously to insure that the lines at intersecting walls meet. On gypsum board, plaster, or paneled walls, install wall angles as shown in Figure 61 with nails, screws, or toggle bolts. On masonry walls, use anchors or concrete nails spaced 24 inches apart.
Figure 61 – Wall angle installation.
Make sure the wall angle is level.
Overlap or miter the wall angle at corners, as shown in Figure 62. After the wall angles are installed the next step is to attach the suspension wires.
Figure 62 – Corner treatment.
Suspension wires are required every 4 feet along main tees and on each side of all splices, as shown in Figure 63.
Figure 63 – Suspension wire installation.
Attach wires to the existing ceiling with nails or screw eyelets. Before attaching the first wire, measure the distance from the wall to the first main tee. Then, stretch a guideline from an opposite wall angle to show the correct position of the first main tee. Position suspension wires for the first tee along the guide. Wires should be cut to proper length, at least 2 inches longer than the distance between the old and new ceiling. Attach additional wires at 4-foot intervals. Pull wires to remove kinks and make 90° bends in the wires where they intersect the guideline. Move the guideline, as required, for each row. After the suspension wires are attached, the next step is to install the main tees.
In an acoustical ceiling, the panels rest on metal members called tees. The tees are suspended by wires.
Main Tees – Install main tees of 12 feet or less by resting the ends on opposite wall angles and inserting the suspension wires, as shown in Figure 64. Hang one wire near the middle of the main tee, level and adjust the wire length, then secure all wires by making the necessary turns in the wire.
Figure 64 – Main tee suspension.
For main tees over 12 feet, cut them so the cross tees do not intersect the main tee at a splice joint. Begin the installation by resting the cut end on the wall angle and attaching the suspension wire closest to the opposite end. Attach the remaining suspension wires, making sure the main tee is level before securing. The remaining tees are installed by making the necessary splices and resting the end on the opposite wall angle. Steel splices are shown in Figure 65 and those for aluminum in Figure 66. After the main tees are installed, leveled, and secured, install the cross tees.
Cross Tees – Aluminum cross tees have high and low tab ends that provide easy positive installation without tools. Installation begins by cutting border tees, when necessary, to fit between the first main tee and the wall angle. Cut off the high tab end and rest this end in the main tee slot. Repeat this procedure until all border tees are installed on one side of the room. Continue across the room, installing the remaining cross tees according to your grid pattern layout. An aluminum cross tee assembly is shown in Figure 67. At the opposite wall angle, cut off the low tab of the border tee and rest the cut end on the wall angle. If the border edge is less than half the length of the cross tee, use the remaining portion of the border of the previously cut tee.
Steel cross tees have the same tab on both ends and, like the aluminum tees, do not require tools for installation. The procedures used in their installation are the same as those just described for aluminum. A steel cross tee assembly is shown in Figure 68. The final step after completion of the grid system is the installation of the acoustical panels.
Panel installation is started by inserting all full ceiling panels. Border panels should be installed last, after they have been cut to proper size. To cut a panel, turn the finish side up, scribe with a sharp utility knife, and saw with a 12 or 14 point handsaw.
Most ceiling panel patterns are random and do not require orientation. However, some fissured panels are designed to be installed in a specific direction and are so marked on the back with directional arrows. When installing panels on a large project, you should work from several cartons, since the color, pattern, or texture might vary slightly; also, by working from several cartons, you avoid a noticeable change in uniformity.
Since ceiling panels are prefinished, handle them with care. Keep their surfaces clean by using talcum powder on your hands or by wearing clean canvas gloves. If panels do become soiled, use an art gum eraser to remove spots, smudges, and fingerprints. Some panels can be lightly washed with a sponge dampened with a mild detergent solution. However, before washing or performing other maintenance services, such as painting, refer to the manufacturer’s instructions.
Ceiling tile can be installed in several ways, depending on the type of ceiling or roof construction. When a flat-surfaced backing is present, such as between beams of a beamed ceiling in a low-slope roof, tiles are fastened with adhesive as recommended by the manufacturer. A small spot of a mastic type of construction adhesive at each corner of a 12 by 12 inch tile is usually sufficient. When tile is edge matched, stapling is also satisfactory.
Perhaps the most common method of installing ceiling tile uses wood strips nailed across the ceiling joists or roof trusses, as shown in Figure 69, view A. These are spaced a minimum of 12 inches OC. A nominal 1 by 3 inch or 1 by 4 inch wood member can be used for roof or ceiling members spaced not more than 24 inches OC. A nominal 2 by 2 inch or 2 by 3 inch member should be satisfactory for truss or ceiling joist spacing of up to 48 inches.
Figure 69 – Ceiling tile assembly.
In locating the strips, first measure the width of the room (the distance parallel to the direction of the ceiling joists). If, for example, this is 11 feet 6 inches, use ten 12 inch square tiles and 9 inch wide tile at each side edge. The second wood strips from each side are positioned so that they center the first row of tiles that can now be ripped to a width of 9 inches. The last row will also be 9 inches, but do not rip these tiles until the last row is reached, so that they fit tightly. The tile can be fitted and arranged the same way for the ends of the room.
Ceiling tiles normally have a tongue on two adjacent sides and a groove on the opposite adjacent sides. Start with the leading edge ahead and to the open side so that it can be stapled to the nailing strips. A small finish nail or adhesive should be used at the edge of the tiles in the first row against the wall. Stapling is done at the leading edge and the side edge of each tile, as shown in Figure 69, view B. Use one staple at each wood strip at the leading edge and two at the open side edge. At the opposite wall, a small finish nail or adhesive must again be used to hold the tile in place. Since most ceiling tile of this type has a factory finish, painting or finishing is not required after it is placed. Take care not to mar or soil the surface.
Test your Knowledge
6. In what order should the following items be installed?
- a. Acoustic panels
- b. Cross tees
- c. Wall angles
- d. Suspension wires
- e. Main tees
- A. a, b, c, d, e
- B. b, e, c, a, d
- C. c, d, e, b, a
- D. d, e, b, c, a
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Numerous flooring materials now available may be used over a variety of floor systems. Each has a property that adapts it to a particular usage. Of the practical properties, perhaps durability and ease of maintenance are the most important, although initial cost, comfort, and appearance must also be considered. Specific service requirements may call for special properties, such as resistance to hard wear in warehouses and on loading platforms, or comfort to users in offices and shops.
There is a wide selection of wood materials used for flooring. Hardwoods and softwoods are available as strip flooring in a variety of widths and thicknesses, and as random width planks and block flooring. Other materials include linoleum, asphalt, rubber, cork, vinyl, and tile and sheet forms. Tile flooring is also available in a particleboard, which is manufactured with small wood particles combined with resin and formed under high pressure. In many areas, ceramic tile and carpeting are used in ways not considered practical a few years ago. Plastic floor coverings used over concrete or a stable wood subfloor are another variation in the types of finishes available.
Softwood finish flooring costs less than most hardwood species and is often used to good advantage in bedroom and closet areas where traffic is light. It is less dense and less wear-resistant than the hardwoods, and shows surface abrasions more readily. Softwoods most commonly used for flooring are southern pine, Douglas fir, redwood, and western hemlock.
Softwood flooring has tongue and groove edges and may be hollow backed or grooved. Some types are also end matched. Vertical grain flooring generally has better wearing qualities than flat grain flooring under hard usage.
Hardwoods most commonly used for flooring are red and white oak, beech, birch, maple, and pecan, any of which can be prefinished or unfinished.
Hardwood strip flooring is available in widths ranging from 1 1/2 to 3 1/4 inches. Standard thicknesses include 3/8, 1/2, and 3/4 inch. A useful feature of hardwood strip flooring is the undercut. There is a wide groove on the bottom of each piece that enables it to lay flat and stable, even when the subfloor surface is slightly uneven.
These strips are laid lengthwise in a room and normally at right angles to the floor joists. A subfloor of diagonal boards or plywood is normally used under the finish floor. The strips are tongue and groove and end matched, as shown in Figure 70.
Figure 70 – Hardwood strip flooring.
Strips are of random length and may vary from 2 to more than 16 feet. The top is slightly wider than the bottom so that tight joints result when flooring is laid. The tongue fits tightly into the groove to prevent movement and floor squeaks.
Figure 71 – Thin strip flooring.
Thin strip flooring, shown in Figure 71, is made of 3/8 by 2 inch strips. This flooring is commonly used for remodeling work or when the subfloor is edge blocked or thick enough to provide very little deflection under loads.
Figure 72 – Square-edged strip flooring.
Square-edged strip flooring, shown in Figure 72, is also occasionally used. The strips are usually 3/8 inch by 2 inches and laid over a substantial subfloor. Face nailing is required for this type of flooring.
Plank floors are usually laid in random widths. The pieces are bored and plugged to simulate wooden pegs originally used to fasten them in place. Today, this type of floor has tongue and groove edges. It is laid similar to regular strip flooring. Solid planks are usually 3/4 inch thick. Widths range from 3 to 9 inches in multiples of 1 inch.
Flooring should be laid after drywall, plastering, or other interior wall and ceiling finish is completed and dried out. Windows and exterior doors should be in place, and most of the interior trim, except base, casing, and jambs, should be installed to prevent damage by wetting or construction activity.
Board subfloors should be clean and level, and covered with felt or heavy building paper. The felt or paper stops a certain amount of dust, somewhat deadens sound, and where a crawl space is used, increases the warmth of the floor by preventing air infiltration. As a guide to provide nailing into the joists, wherever possible, mark the location of the joists with a chalk line on the paper. Plywood subflooring does not normally require building paper.
Figure 73 – Application of strip flooring.
Strip flooring should normally be laid crosswise to the floor joists, as shown in Figure 73. In conventional structures, the floor joists span the width of the building over a center-supporting beam or wall. Thus, the finish flooring of the entire floor areas of a rectangular structure will be laid in the same direction. Flooring with L- or I-shaped plans will usually have a direction change, depending on joist direction. As joists usually span the short way in a room, the flooring will be laid lengthwise to the room. This layout has a pleasing appearance and also reduces shrinkage and swelling of the flooring during seasonal changes.
When the flooring is delivered, store it in the warmest and driest place available in the building. Moisture absorbed after delivery to the building site is the most common cause of open joints between flooring strips that appear after several months of the heating season.
Floor squeaks are usually caused by the movement of one board against another. Such movement can occur for a number of reasons: floor joists may be too light, causing excessive deflection; sleepers over concrete slabs may not be held down tightly; there may be loose fitting tongues or poor nailing. Adequate nailing is an important means of minimizing squeaks. Another is to apply the finish floors only after the joists have dried to 12 percent moisture content or less. A much better job results when it is possible to nail through the finish floor, through the subfloor, and into the joists than if the finish floor is nailed only to the subfloor.
Various types of nails are used in nailing different thicknesses of flooring. Before using any type of nail, you should check with the floor manufacturer’s recommendations as to size and diameter for specific uses. Flooring brads are also available with blunted points to prevent splitting the tongue.
Figure 74 – Nailing the first strip.
Figure 74 shows how to nail the first strip of flooring. This strip should be placed 1/2 to 5/8 inch away from the wall. The space is to allow for expansion of the flooring when moisture content increases. The first nails should be driven straight down through the board at the groove edge. The nails should be driven into the joist and near enough to the edge so that they will be covered by the base or shoe molding. The first strip of flooring can also be nailed through the tongue, as shown in Figure 75.
Figure 75 shows in detail how nails should be driven into the tongue of the flooring at an angle of 45° to 50°. Do not drive the nails flush; this prevents damaging the edge by the hammer head, as shown in Figure 76. These nails should be set with a nail set.
To prevent splitting the flooring, pre-drill through the tongue, especially at the ends of the strip. For the second course of flooring from the wall, select pieces so that the butt joints are well separated from those in the first course. Under normal conditions, each board should be driven up tightly against the previous board. Cracked pieces may require wedging to force them into alignment or may be cut and used at the ends of the course or in closets. In completing the flooring, you should provide a 1/2 to 5/8 inch space **68 between the wall and the last flooring strip. This strip should be face nailed just like the first strip so that the base or shoe covers the set nailheads, as shown in Figure 74.
One of the most critical factors in applying wood flooring over concrete is the use of a good vapor barrier under the slab to resist ground moisture. The vapor barrier should be placed under the slab during construction. An alternate method must be used when the concrete is already in place, as shown in Figure 77.
A system of preparing a base for wood flooring when there is a vapor barrier under the slab is shown in Figure 78.
Treated 1 by 4 inch furring strips should be anchored to the existing slab. Shims can be used, when necessary, to provide a level base. Strips should be spaced no more than 16 inches on center (OC). A good waterproof or water vapor resistant coating on the concrete before the treated strips are installed is usually recommended to aid in further reducing moisture movement. A vapor barrier, such as a 4 mil polyethylene or similar membrane, is then laid over the anchored 1 by 4 inch wood strips and a second set of 1 by 4s nailed to the first. Use 1 1/2 inch-long nails spaced 12 to 16 inches apart in a staggered pattern. The moisture content of these second members should be approximately the same as that of the strip flooring to be applied. Strip flooring can then be installed as previously described.
When other types of finish floor, such as a resilient tile, are used, plywood underlayment is placed over the 1 by 4s as a base.
Wood block (parquet) flooring, shown in Figure 79, is used to produce a variety of elaborate designs formed by small wood block units. A block unit consists of short lengths of flooring, held together with glue, metal splines, or other fasteners. Square and rectangular units are produced. Generally, each block is laid with its grain at right angles to the surrounding units.
Figure 79 – Wind block (parquet) laminated flooring.
Blocks, called laminated units, are produced by gluing together several layers of wood. Unit blocks are commonly produced in 3/4 inch thicknesses. Dimensions (length and width) are in multiples of the widths of the strips from which they are made. For example, squares assembled from 2 1/4 inch strips are 6 3/4 by 6 3/4 inches, 9 by 9 inches, or 11 1/4 by 11 1/4 inches. Wood block flooring is usually tongue and groove.
Flooring materials such as asphalt, vinyl, linoleum, and rubber usually reveal rough or irregular surfaces in the flooring structure upon which they are laid. Conventional subflooring does not provide a satisfactory surface. An underlayment of plywood or hardboard is required. On concrete floors, a special mastic material is sometimes used when the existing surface is not suitable as a base for the finish flooring.
An underlayment also prevents the finish flooring materials from checking or cracking when slight movements take place in a wood subfloor. When used for carpeting and resilient materials, the underlayment is usually installed as soon as wall and ceiling surfaces are complete.
Hardboard and particleboard both meet the requirements of an underlayment board. The standard thickness for hardboard is 1/4 inch. Particleboard thicknesses range from 1/4 to 3/4 inch.
This type of underlayment material will bridge small cups, gaps, and cracks. Larger irregularities should be repaired before the underlayment is applied. High spots should be sanded down and low areas filled. Panels should be unwrapped and placed separately around the room for at least 24 hours before they are installed. This equalizes the moisture content of the panels before they are installed.
Installation – To install hardboard or particleboard, start at one corner and fasten each panel securely before laying the next. Some manufacturers print a nailing pattern on the face of the panel. Allow at least a 1/8 to 3/8 inch space next to a wall or any other vertical surface for panel expansion.
Stagger the joints of the underlayment panel. The direction of the continuous joints should be at right angles to those in the subfloor. Be especially careful to avoid aligning any joints in the underlayment with those in the subfloor. Leave a 1/32 inch space at the joints between hardboard panels. Particleboard panels should be butted lightly.
Fasteners – Underlayment panels should be attached to the subfloor with approved fasteners. Examples are shown in Figure 80.
Figure 80 – Fasteners for underlayment.
For hardboard, space the fasteners 3/8 inch from the edge. Spacing for particleboard varies for different thicknesses. Be sure to drive nail heads flush. When fastening underlayment with staples, use a type that is etched or galvanized and at least 7/8 inch long. Staples should not be spaced over 4 inches apart along panel edges.
Special adhesives can also be used to bond underlayment to subfloors. They eliminate the possibility of nail-popping under resilient floors.
Plywood is preferred by many for underlayment. It is dimensionally stable, and spacing between joints is not critical. Since a range of thicknesses is available, alignment of the surfaces of various finish flooring materials is easy. An example of aligning resilient flooring with wood strip flooring is shown in Figure 81.
Figure 81 – Alignment of finish flooring materials.
To install plywood underlayment, follow the same general procedures described for hardboard. Turn the grain of the faceply at right angles to the framing supports. Stagger the end joints. Nails may be spaced farther apart for plywood but should not exceed a field spacing of 10 inches (8 inches for 1/4 and 3/8 inch thicknesses) and an edge spacing of 6 inches OC. You should use ring-grooved or cement-coated nails to install plywood underlayment.
Test your Knowledge
7. What factor usually causes cracks to appear in finish floors several months after the floor has been laid?
- A. Expansion of subfloor material
- B. Absorption of moisture after delivery
- C. Poor nailing
- D. Weak floor joists
- Return to Table of Contents -
Resilient flooring can be made of several different materials, including vinyl, rubber, and linoleum. It is available in tiles and rolls.
After the underlayment is securely fastened, sweep and vacuum the surface carefully. Check to see that surfaces are smooth and joints level. Rough edges should be removed with sandpaper or a block plane.
The smoothness of the surface is extremely important, especially under the more pliable materials such as vinyl, rubber, and linoleum. Over a period of time, these materials will telegraph, or show on the surface even the slightest irregularities or rough surfaces. Linoleum is especially susceptible. For this reason, a base layer of felt is often applied over the underlayment when linoleum, either in tile or sheet form, is installed.
Because of the many resilient flooring materials on the market, it is essential that each application be made according to the recommendations and instructions furnished by the manufacturer of the product.
Start a floor tile layout by locating the center of the end walls of the room. Disregard any breaks or irregularities in the contour. Establish a main centerline by snapping a chalk line between these two points. When snapping long lines, remember to hold the line at various intervals and snap only short sections.
Next, lay out another center line at right angles to the main center line. This line should be established by using a framing square or setting up a right triangle, as shown in Figure 82, with length 3 feet, height 4 feet, and hypotenuse 5 feet. In a large room, a 6:8:10 foot triangle can be used. To establish this triangle, you can either use a chalk line or draw the line along a straightedge.
Figure 82 – Establishing center for laying floor tile.
With the centerlines established, make a trial layout of tile along the center lines. Measure the distance between the wall and last tile. If the distance is less than 2 inches or more than 8 inches, move the centerline half the width of the tile (4 1/2 inches for a 9 by 9 tile) closer to the wall. This adjustment eliminates the need to install border tiles that are too narrow. As you will learn shortly, border tiles are installed as a separate operation after the main area has been tiled. Check the layout along the other center line in the same way. Since the original center line is moved exactly half the tile size, the border tile will remain uniform on opposite sides of the room. After establishing the layout, you are now ready to spread the adhesive.
Spreading Adhesive – Before you spread the adhesive, reclean the floor surface. Using a notched trowel, spread the adhesive over one quarter of the total area bringing the spread up to the chalk line but not covering it. Be sure the depth of the adhesive is the depth recommended by the manufacturer.
The spread of adhesive is very important. If it is too thin, the tile will not adhere properly. If it is too heavy, the adhesive will bleed between the joints.
Allow the adhesive to take an initial set before a single tile is laid. The time required will vary from a minimum of 15 minutes to a much longer time, depending on the type of adhesive used. Test the surface with your thumb. It should feel slightly tacky but should not stick to your thumb.
Laying the Tile – Start laying the tile at the center of the room. Make sure the edges of the tile align with the chalk line. If the chalk line is partially covered with the adhesive, snap a new one or tack down a thin, straight strip of wood to act as a guide in placing the tile.
Butt each tile squarely to the adjoining tile, with the comers in line. Carefully lay each tile in place. Do not slide the tile; this causes the adhesive to work up between the joints and prevents a tight fit. Take sufficient time to position each tile correctly. There is usually no hurry since most adhesives can be worked over a period of several hours.
To remove air bubbles, rubber, vinyl, and linoleum are usually rolled after a section of the floor is laid. Be sure to follow the manufacturer’s recommendations. Asphalt tile does not need to be rolled.
After the main area is complete, set the border tile as a separate operation. To lay out a border tile, place a loose tile (the one that will be cut and used) over the last tile in the outside row. Now, take another tile and place it in position against the wall and mark a sharp pencil line on the first tile, as shown in Figure 83.
Figure 83 – Layout of a border tile.
Cut the tile along the marked line, using heavy duty shears or tin snips. Some types of tile require a special cutter or they may be scribed and broken. Asphalt tile, if heated, can be easily cut with snips.
After all sections of the floor have been completed, install the cove along the wall and around fixtures. A special adhesive is available for this operation. Cut the proper lengths and make a trial fit. Apply the adhesive to the cove base and press it into place.
Check the completed installation carefully. Remove any spots of adhesive. Work carefully using cleaners and procedures approved by the manufacturer.
Self-Adhering Tile – Before installing self-adhering tile, you must first ensure that the floors are dry, smooth, and completely free of wax, grease, and dirt. Generally, tiles can be laid over smooth-faced resilient floors. Embossed floors, urethane floors, or cushioned floors should be removed.
Self-adhering tile is installed in basically the same way as previously mentioned types of tile. Remove the paper from the back of the tile, place the tile in position on the floor, and press it down.
Use Table 3 when estimating resilient floor tile materials. This table gives you approximate square feet coverage per gallon of different types of primer and adhesives.
Table 3 – Estimating
Adhesive for Floor Tile.
Be sure to read and follow the manufacturer’s directions. Table 4 provides figures for estimating the two sizes of tile most commonly used. After calculating the square feet of the area to be tiled, refer to the table to find the number of tiles needed, then add the waste factor.
Table 4 – Estimating Floor Tile.
To find the number of tiles required for an area not shown in this table, such as the number of 9 by 9 inch tiles required for an area of 550 square feet, add the number of tiles needed for 50 square feet to the number of tile needed for 500 square feet. The result will be 979 tiles, to which you must add 5 percent for waste. The total number of tiles required is 1,028.
When tiling large areas, work from several different boxes of tile. This will avoid concentrating one color shade variation in one area of the floor.
Because of its flexibility, vinyl flooring is very easy to install. Since sheets are available in 6- to 12-foot widths, many installations can be made free of seams. Flexible vinyl flooring is fastened down only around the edges and at seams. It can be installed over concrete, plywood, or old linoleum.
To install, spread the sheet smoothly over the floor. Let excess material turn up around the edges of the room. Where there are seams, carefully match the pattern. Fasten the two sections to the floor with adhesive. Trim the edges to size by creasing the vinyl sheet material at intersections of the floor and walls and cutting it with a utility knife drawn along a straightedge. Be sure the straightedge is parallel to the wall.
After the edges are trimmed and fitted, secure them with a staple gun, or use a band of double faced adhesive tape. Always study the manufacturer’s directions carefully before starting the work.
Test your Knowledge
8. What is the result of too heavily applied tile adhesive?
- A. Tile will not adhere.
- B. Adhesive will not set.
- C. Tiles will telegraph.
- D. Adhesive will bleed between tiles.
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Wall to wall carpeting can make a small room look larger, insulate against drafty floors, and do a certain amount of soundproofing. Carpeting is not difficult to install. All carpets consist of a surface pile and backing. The surface pile may be nylon, polyester, polypropylene, acrylic, wool, or cotton. Each has its advantages and disadvantages. The type you select depends on your needs. Carpeting can be purchased in 9-, 12-, and 15-foot widths.
Measure the room in the direction in which the carpet will be laid. To broaden long, narrow rooms, lay patterned or striped carpeting across the width. For conventionally rectangular rooms, measure the room lengthwise. Include the full width of doorframes so the carpet will extend slightly into the adjoining room. When measuring a room with alcoves or numerous wall projections, calculate on the basis of the widest and longest points. This will result in some waste material, but is safer than ordering less than what you need.
Most wall-to-wall carpeting is priced by the square yard. To determine how many square yards you need, multiply the length by the width of the room in feet and divide the result by 9.
Except for so-called one-piece and cushion-backed carpeting, underlayment or padding is essential to a good carpet installation. It prolongs the life of the carpeting, increases its soundproofing qualities, and adds to underfoot comfort.
The most common types of carpet padding are latex (rubber), sponge rubber foams, soft and hardback vinyl foams, and felted cushions made of animal hair or of a combination of hair and jute. Of all types, the latex and vinyl foams are generally considered the most practical. Their waffled surface tends to hold the carpet in place. Most carpet padding comes in a standard 4 1/2 foot width.
Cushion-backed carpeting is increasing in popularity, especially with do-it-yourself homeowners. The high-density latex backing is permanently fastened to the carpet, which eliminates the need for a separate underpadding. It is nonskid and heavy enough to hold the carpet in place without the use of tacks. In addition, the foam rubber backing keeps the edges of the carpet from unraveling so that it need not be bound. Foam rubber is mildewproof and unaffected by water, so the carpet can be used in basements and other below-grade installations. It can even be laid directly over unfinished concrete.
The key feature of this backing, however, is the dimensional stability it imparts to the carpet. This added characteristic means the carpet will not stretch, nor will it expand and contract from temperature or humidity changes. Because of this, these carpets can be loose laid, with no need for adhesive or tacks to give them stability.
To lay carpets successfully on wood floors, you must ensure that the surface is free of warps, and that all nails and tacks are either removed or hammered flush. Nail down any loose floorboards and plane down the ridges of warped boards. Fill wide cracks between floorboards with strips of wood or wood putty. Cover floors that are warped and cracked beyond reasonable repair with hardboard or plywood.
Stone or concrete floors that have surface ridges or cracks should be treated beforehand with a floor leveling compound to reduce carpet wear. These liquid compounds are also useful for sealing the surface of dusty or powdery floors. A thin layer of the compound, which is floated over the floor, will keep dust from working its way up through the underlayment and into the carpet pile.
The best carpeting for concrete and hard tile surfaces is the indoor-outdoor type. The backing of this carpet is made of a closed-pore type of either latex or vinyl foam, which keeps out most moisture. It is not wise to lay any of the standard paddings on top of floor tiles unless the room is well ventilated and free of condensation. Vinyl and asbestos floor tiles accumulate moisture when carpeting is laid over them. This condensation soaks through into the carpet and eventually causes a musty odor. It can also produce mildew stains.
The standard fastening methods are with tacks or by means of tackless fittings. Carpets can also be loose laid with only a few tacks at entrances. Carpet tack lengths are 3/4 and 1 inch. The first is long enough to go through a folded carpet hem and anchor it firmly to the floor, as shown in Figure 84. The 1-inch tacks are used in corners where the folds of the hem make three thicknesses.
Figure 84 – Carpet installation using tacks.
Tackless fittings, shown in Figure 85, are a convenient fastening method. They consist of a 4-foot wooden batten with a number of spikes projecting at a 60° angle. The battens are nailed to the floor around the entire room, end to end and 1/4 inch from the baseboard, with the spikes facing toward the wall. The spikes grip the backing of the carpet to hold it in place. On stone or concrete floors, the battens are glued in place with special adhesives.
Figure 85 – Tackless Fitting for Doorway (Left) and Wall (Right).
Though cushion-backed carpeting can stay in place without fastening, securing with double-face tape is the preferred method. Carpets can also be attached to the floor with Velcro™ tape where the frequent removability of the carpet for cleaning and maintenance is a factor.
To install a carpet, you will need a hammer, large scissors, a sharp knife, a 3 foot rule, needle and carpet thread, chalk and chalk line, latex adhesive, and carpet tape. The only specialized tool you will need is a carpet stretcher, often called a knee kicker.
Before starting the job, remove all furniture and any doors that swing into the room. When cutting the carpet, spread it out on a suitable floor space and chalk the exact pattern of the room on the pile surface; then cut along the chalk line with the scissors or sharp knife.
Join unseamed carpet by placing the two pieces so the pile surfaces meet edge to edge. Match patterned carpets carefully. With plain carpets, lay each piece so the piles run the same way. Join the pieces with carpet thread, taking stitches at 18 inch intervals along the seam. Pull the carpet tight after each stitch to take up slack. Sew along the seam between stitches. Tuck any protruding fibers back into the pile. Carpet can also be seamed by cementing carpet tape to the backing threads with latex adhesive.
Open the carpet to room length and position it before starting to put down the padding. The pile should fall away from windows to avoid uneven shading in daylight. Fold one end of the carpet back halfway and put the padding down on the exposed part of the floor. Do the same at the other end. This avoids wrinkles caused by movement of the padding.
To tack, start at the corner of the room that is formed by the two walls with the fewest obstructions. Butt the carpet up against the wall, leaving about 1 1/2 inches up the baseboard for hemming. Attach the carpet temporarily with tacks about 6 inches from the baseboard along these two walls. Use the knee kicker to stretch the carpet, first along the length, then the width. Start from the middle of the wall, stretching alternately toward opposite comers. When the carpet is smooth, tack down the stretched area temporarily.
Cut slots for pipes, fireplace protrusions, and radiators. Trim back the padding to about 2 inches from the wall to leave a channel for the carpet hem. Fold the hem under and tack the carpet in place with a tack every 5 inches. Be sure the tacks go through the fold.
Figure 86 – Carpet installation using tackless fastenings.
When installing carpet, use tackless fastening strips, as shown in Figure 86. Position and trim the padding (View B) so that it meets the strip at the wall, but does not overlap the strip. Tack it down so it does not move. Lay out the carpeting and, using a kneekicker, stretch the carpet over the nails projecting out of the tackless strip (View C). Trim the carpet, leaving a 3/8 inch overlap, which is tucked into place between the wall and the tackless strip (View D). (If you trim too much carpeting, lift the carpeting off the spikes of the tackless strip and use the knee-kicker to restretch the carpet (View E). Protect the exposed edge of the carpet at doorways with a special metal binder strip or bar (View F). The strip is nailed to the floor at the doorway and the carpet slipped under a metal lip, which is then hammered down to grip the carpet edge.
Tacks can be used as an alternative to a binder strip. Before tacking, tape the exposed edge of woven carpet to prevent fraying if the salvage has been trimmed off. Cement carpet tape to the backing threads with latex adhesive. Nonwoven or latex-backed carpet will not fray, but tape is still advisable to protect exposed edges. Any door that drags should be removed and trimmed.
When installing cushion-backed carpeting, you can eliminate several steps. For instance, you do not need to use tack strips or a separate padding. Although these instructions apply to most such carpeting, read the manufacturer’s instructions for any deviation in technique or use of material.
To install a cushioned carpet, apply 2-inch wide double-face tape flush with the wall around the entire room, as shown in Figure 87, view A. Roll out and place the carpet. Fold back the carpet and remove the protective paper from the tape. Press the carpet down firmly over the tape and trim away excess, as shown in view B. A metal binder strip or an aluminum saddle is generally installed in doorways, as shown in view C. If your room is wider than the carpet, you will have to seam two pieces together. Follow the manufacturer’s recommendations.
Figure 87 – Installing cushion-backed carpeting.
Test your Knowledge
9. How many square yards of carpet are required to cover a room 24 feet by 48 feet?
- A. 76
- B. 98
- C. 114
- D. 128
- Return to Table of Contents -
The final stage of most construction projects is the application of protective coatings, or painting. As with all projects, you should follow the plans and specifications for surface preparation and application of the finish coat. The specifications give all the information you need to complete the tasks. But to have a better understanding of structural coatings, you need to know their purposes, methods of surface preparation, and application techniques.
The protection of surfaces is the most important consideration in determining the maintenance cost of structures. Structural coatings serve as protective shields between the base construction materials and elements that attack and deteriorate them. Regularly programmed structural coatings offer long-range protection, extending the useful life of a structure.
The primary purpose of a structural coating is protection. This is provided initially with new construction and maintained by a sound and progressive preventive maintenance program. Programmed painting enforces inspection and scheduling. A viable preventive **81 maintenance program helps ensure that minor problems are detected at an early stage, before they become major failures. An added advantage derived from preventive maintenance is the detection of faulty structural conditions or problems caused by leakage or moisture.
Resistance to moisture from rain, snow, ice, and condensation constitutes perhaps the greatest single protective characteristic of paint, the most common type of structural coating. Moisture causes metal to corrode and wood to swell, warp, or rot. Interior wall finishes of buildings can be ruined by moisture entering through neglected exterior surfaces. Porous masonry is attacked and destroyed by moisture. Paint films must be as impervious to moisture as possible to provide a protective, waterproof film over the surface to which they are applied. Paint also acts as a protective film against acids, alkalies, material organisms, and other damaging elements.
Painting is an essential part of general maintenance programs for hospitals, kitchens, mess halls, offices, warehouses, and living quarters. Paint coatings provide smooth, non-absorptive surfaces that are easily washed and kept free of dirt and foodstuffs. Adhering foodstuffs harbor germs and cause disease. Coating rough or porous areas seals out dust and grease that would otherwise be difficult to remove.
Odorless paints are used in these areas because conventional paint solvent odors are obnoxious to personnel. In food preparation areas, the odors may be picked up by nearby food.
Certain types of structural coatings delay the spread of fire and assist in confining a fire to its area of origin. Fire-retardant coatings should not be considered substitutes for conventional paints. The use of fire-retardant coatings is restricted to areas of highly combustible surfaces, and must be justified and governed by the specific agency’s criteria. Fire-retardant coatings are not used in buildings containing automatic sprinkler systems.
Camouflage paints have special properties that make them different from conventional paints. Their uses are limited to special applications. Do not use camouflage paints as substitutes for conventional paints. Use this paint only on exterior surfaces to render buildings and structures inconspicuous by blending them in with the surrounding environment.
White and light-tinted coatings applied to ceilings and walls reflect both natural and artificial light, and help brighten rooms and increase visibility. On the other hand, darker colors reduce the amount of reflected light. Flat coatings diffuse, soften, and evenly distribute illumination, whereas gloss finishes reflect more like mirrors and may create glare. Color contrasts improve visibility of the painted surface, especially when paint is applied in distinctive patterns. For example, white on black, white on orange, or yellow on black can be seen at greater distances than single colors or other combinations of colors.
Certain colors are used as standard means of identifying objects and promoting safety. For example, fire protection equipment is painted red. Containers for kerosene, gasoline, solvents, and other flammable liquids should be painted a brilliant yellow and marked with large black letters to identify their contents. Colors of signal lights and painted signs help control traffic safely by providing directions and other travel information.
As a builder, you must consider many factors when selecting a coating for a particular job. One important factor is the type of coating, which depends on the composition and properties of the ingredients.
Paint is composed of various ingredients, such as pigment, nonvolatile vehicle (or binder), and solvent (or thinner). Other coatings may contain only a single ingredient.
In this section, we’ll cover the basic components of paint (pigment, vehicles, and solvents) and explain the characteristics of different types of paint.
Paint is composed of two basic ingredients, pigment and a vehicle. A thinner may be added to change the application characteristics of the liquid.
Pigments are insoluble solids, ground finely enough to remain suspended in the vehicle for a considerable time after thorough stirring or shaking. Opaque pigments give the paint its hiding, or covering, capacity and contribute other properties; white lead, zinc oxide, and titanium dioxide are examples. Color pigments give the paint its color. These may be inorganic, such as chrome green, chrome yellow, and iron oxide, or organic, such as toluidine red and phthalocyanine blue. Transparent or extender pigments contribute bulk and also control the application properties, durability, and resistance to abrasion of the coating. There are other special purpose pigments, such as those enabling paint to resist heat, control corrosion, or reflect light.
The vehicle, or binder, of paint is the material holding the pigment together and causing paint to adhere to a surface. In general, paint durability is determined by the resistance of the binder to the exposure conditions. Linseed oil, once the most common binder, has been replaced mainly by the synthetic alkyd resins. These result from the reaction of glycerol phthalate and an oil and may be made with almost any property desired. Other synthetic resins, used either by themselves or mixed with oil, include phenolic resin, vinyl, epoxy, urethane, polyester, and chlorinated rubber. Each has its own advantages and disadvantages. When using these materials, it is particularly important that you follow the manufacturer’s instructions exactly.
The only purpose of a solvent, or thinner, is to adjust the consistency of the material so that it can be applied readily to the surface. The solvent then evaporates, contributing nothing further to the film. For this reason, the cheapest suitable solvent should be used. This solvent is likely to be naphtha or mineral spirits. Although turpentine is sometimes used, it contributes little that other solvents do not and costs much more.
Synthetic resins usually require a special solvent. It is important the correct one be used; otherwise, the paint may be spoiled entirely.
Paints by far comprise the largest family of structural coatings you will be using to finish products, both interior and exterior. In the following section, we will cover some of the most commonly encountered types.
Oil-based paints consist mainly of a drying oil, usually linseed, mixed with one or more pigments. The pigments and quantities of oil in oil paints are usually selected on the basis of cost and their ability to impart to the paint the desired properties, such as durability, economy, and color. An oil-based paint is characterized by easy application and slow drying. It normally chalks in such a manner as to permit recoating without costly surface preparation. Adding small amounts of varnish tends to decrease the time it takes an oil-based paint to dry and to increase the paint’s resistance to water. Oil-based paints are not recommended for surfaces submerged in water.
Enamels are generally harder, tougher, and more resistant to abrasion and moisture penetration than oil-based paints. Enamels are available in flat, semigloss, and gloss. The extent of pigmentation in the paint or enamel determines its gloss. Gloss is reduced by adding lower cost pigments called extenders. Typical extenders are calcium carbonate (whiting), magnesium silicate (talc), aluminum silicate (clay), and silica. The level of gloss depends on the ratio of pigment to binder.
Epoxy paints are a combined resin and a polyamide hardener that are mixed before use. When mixed, the two ingredients react to form the end product. Epoxy paints have a limited working, or pot, life, usually 1 working day. They are outstanding in hardness, adhesion, and flexibility, plus they resist corrosion, abrasion, alkali, and solvents. The major uses of epoxy paints are as tile-like glaze coatings for concrete or masonry, and for structural steel in corrosive environments. Epoxy paints tend to chalk on exterior exposure; low gloss levels and fading can be anticipated. Otherwise, their durability is excellent.
Latex paints contain a synthetic chemical, called latex, dispersed in water. The kinds of latex usually found in paints are styrene butadiene (also called synthetic rubber), polyvinyl acetate (PVA or vinyl), and acrylic. Latex paints differ from other paints in that the vehicle is an emulsion of binder and water. Being water-based, latex paints have the advantage of being easy to apply. They dry through evaporation of the water. Many latex paints have excellent durability. This makes them particularly useful for coating plaster and masonry surfaces. Careful surface preparation is required for their use.
Rubber-based paints are solvent thinned and should not be confused with latex binders, often called rubber-based emulsions. Rubber-based paints are lacquer-type products and dry rapidly to form finishes highly resistant to water and mild chemicals. They are used for coating exterior masonry and areas that are wet, humid, or subject to frequent washing, such as laundry rooms, showers, washrooms, and kitchens.
Portland cement mixed with several ingredients acts as a paint binder when it reacts with water. The paints are supplied as a powder to which the water is added before being used. Cement paints are used on rough surfaces, such as concrete, masonry, and stucco. They dry to form hard, flat, porous films that permit water vapor to pass through readily. When properly cured, cement paints of good quality are quite durable. When improperly cured, they chalk excessively on exposure and may present problems in repainting.
Aluminum paints are available in two forms, ready-mixed and ready-to-mix. Ready-mixed aluminum paints are supplied in one package and are ready for use after normal mixing. They are made with vehicles that will retain metallic brilliance after moderate periods of storage. They are more convenient to use and allow for less error in mixing than the ready-to-mix form. Ready-to-mix aluminum paints are supplied in two packages, one containing clear varnish and the other the required amount of aluminum paste (usually two-thirds aluminum flake and one-third solvent). You mix just before using by slowly adding the varnish to the aluminum paste and stirring.
Ready-to-mix aluminum paints allow a wider choice of vehicles and present less of a problem with storage stability. A potential problem with aluminum paints is moisture in the closed container.
When water is present, moisture may react with the aluminum flake to form hydrogen gas that pressurizes the container.
Pressure can cause the container to bulge or even pop the cover off the container. Check the containers of ready-mixed paints for bulging. If they bulge, puncture the covers carefully before opening to relieve the pressure. Be sure to use dry containers when mixing aluminum paints.
In contrast to paints, varnishes contain little or no pigment and do not obscure the surface to which they are applied. Usually a liquid, varnish dries to a hard, transparent coating when spread in a thin film over a surface, affording protection and decoration.
Of the common types of varnishes, the most important are the oils, including spar, flat, rubbing, and color types. These are extensively used to finish and refinish interior and exterior wood surfaces, such as floors, furniture, and cabinets. Spar varnish is intended for exterior use in normal or marine environments, although its durability is limited. To increase durability, exterior varnishes are especially formulated to resist weathering.
Varnishes produce a durable, elastic, and tough surface that normally dries to a high gloss finish that does not easily mar. A lower gloss may be obtained by rubbing the surface with very fine steel wool. It is simpler to use a flat varnish with the gloss reduced by adding transparent flatting pigments, such as certain synthetic silicas. These pigments are dispersed in the varnish to produce a clear finish that dries to a low gloss, but still does not obscure the surface underneath, that is, you can still see the grain of the wood.
Shellac is purified lac formed into thin flakes and widely used as a binder in varnishes, paints, and stains. Lac is a resinous substance secreted by certain insects. The vehicle is wood alcohol. The natural color of shellac is orange, although it can be obtained in white. Shellac is used extensively as a finishing material and a sealant. Applied over knots in wood, it prevents bleeding.
Lacquers may be clear or pigmented and can be lusterless, semigloss, or glossy. Lacquers dry or harden quickly, producing a firm oil and water-resistant film. Many coats are required to achieve adequate dry film thickness. It generally costs more to use lacquers than most paints.
Stains are obtainable in four different kinds: oil, water, spirit, and chemical. Oil stains have an oil vehicle; mineral spirits can be added to increase penetration. Water stains are solutions of aniline dyes and water. Spirit stains contain alcohol. Chemical stains work by means of a chemical reaction when dissolved by water. The type of stain to use depends largely on the purpose, the location, and the type of wood being covered.
The most essential part of any painting job is proper surface preparation and repair. Each type of surface requires specific cleaning procedures. Paint will not adhere well, provide the protection necessary, or have the desired appearance unless the surface is in proper condition for painting. Exterior surface preparation is especially important because hostile environments can accelerate deterioration.
As a Builder, you are most likely to paint three types of metals: ferrous, nonferrous, and galvanized. Improper protection of metals is likely to cause fatigue in the metal itself and may result in costly repairs or even replacement. Correct surface preparation prior to painting is essential.
Cleaning ferrous metals, such as iron and steel, involves the removal of oil, grease, previous coatings, and dirt. Keep in mind that once you prepare a metal surface for painting, it will start to rust immediately unless you use a primer or pretreatment to protect the surface.
The nonferrous metals are brass, bronze, copper, tin, zinc, aluminum, nickel, and others not derived from iron ore. Nonferrous metals are generally cleaned with a solvent type of cleaner. After cleaning, you should apply a primer coat or a pretreatment.
Galvanized iron is one of the most difficult metals to prime properly. The galvanizing process forms a hard, dense surface that paint cannot penetrate. Too often, galvanized surfaces are not prepared properly, resulting in paint failure. Three steps must be taken to develop a sound paint system.
Concrete and masonry are normally not painted unless painting is required for damp-proofing. Cleaning concrete and masonry involves the removal of dirt, mildew, and efflorescence, which is a white, powdery crystalline deposit that often forms on concrete and masonry surfaces.
Dirt and fungus are removed by washing with a solution of trisodium phosphate. The strength of the solution may vary from 2 to 8 ounces per gallon of water, depending upon the amount of dirt or mildew on the surface. Immediately after washing, rinse off all the trisodium phosphate with clear water. If using oil paint, allow the surface to dry thoroughly before painting.
For efflorescence, first remove as much of the deposit as possible by dry brushing with a wire brush or a stiff fiber brush. Next, wet the surface thoroughly with clear water; and then scrub with a stiff brush dipped in a 5 percent solution by weight of muriatic acid. Allow the acid solution to remain on the surface about 3 minutes before scrubbing, but rinse thoroughly with clear water immediately after scrubbing. Work on small areas not larger than 4 square feet. Wear rubber gloves, a rubber apron, and goggles when mixing and applying the acid solution. In mixing the acid, always add acid to water. Do not add water to acid, as this can cause the mixture to explode. For a very heavy deposit, the acid solution may be increased to 10 percent and allowed to remain on the surface for 5 minutes before it is scrubbed.
All defects in a concrete or masonry surface must be repaired before painting. To repair a large crack, cut the crack out to an inverted V shape and plug it with grout, which is a mixture of two or three parts of mortar sand, one part of Portland cement, and enough water to make it putty-like in consistency. After the grout sets, damp cure it by keeping it wet for 48 hours. If oil paint is to be used, allow at least 90 days for weathering before painting over a grout-filled crack.
Whenever possible, allow new plaster to age at least 30 days before painting if oilbased paint is being applied. Latex paint can be applied after 48 hours, although a 30- day wait is generally recommended. Before painting, fill all holes and cracks with spackling compound or patching plaster. Cut out the material along the crack or hole in an inverted V shape. To avoid excessive absorption of water from the patching material, wet the edges and bottom of the crack or hole before applying the material. Fill the opening to within 1/4 inch of the surface and allow the material to set partially before bringing the level up flush with the surface. After the material has thoroughly set, **87 depending on the type of filler used, use fine sandpaper to smooth out the rough spots. Plaster and wallboard should have a sealer or a prime coat applied before painting. When working with old work, remove all loose or scaling paint, sand lightly, and wash off all dirt, oil, and stains. Allow the surface to dry thoroughly before applying the new finish coat.
Before being painted, a wood surface should be closely inspected for loose boards, defective lumber, protruding nail heads, and other defects or irregularities. Loose boards should be nailed tight, defective lumber should be replaced, and all nail heads should be countersunk.
A dirty wood surface is cleaned for painting by sweeping, dusting, and washing with solvent or soap and water. In washing wood, take care to avoid excessive wetting, which tends to raise the grain. Wash a small area at a time, then rinse and dry it immediately.
Wood that is to receive a natural finish, not concealed by an opaque coating, may require bleaching to a uniform or light color. To bleach, apply a solution of 1 pound of oxalic acid to 1 gallon of hot water. More than one application may be required. After the solution has dried, smooth the surface with fine sandpaper.
Rough wood surfaces must be sanded smooth for painting. Mechanical sanders are used for large areas, hand sanding for small areas. For hand sanding, you should wrap sandpaper around a rubber, wood, or metal sanding block. For a very rough surface, start with a coarse paper, about No. 2 or 2 1/2. Follow this with a No. 1/2, No. 1, or No. 1 1/2. You should finish with about a No. 2/0 grit. For fine work, such as furniture sanding, you should finish with a finer grit.
Sap or resin in wood can stain through a coat, or even several coats, of paint. Remove sap or resin by scraping or sanding. Knots in resinous wood should be treated with knot sealer.
Green lumber contains a considerable amount of water, most of which must be removed before use. This not only prevents shrinkage after installation, but prevents blistering, cracking, and loss of adhesion after paint is applied. Be sure all lumber used has been properly dried and kept dry before painting.
Conditioners are often applied on masonry to seal a chalky surface to improve adhesion of water-based topcoats. Sealers are used on wood to prevent resin running or bleeding. Fillers are used to produce a smooth finish on open grained wood and rough masonry. Table 5 presents the satisfactory treatments of the various surfaces. **88
Table 5 –
Treatments of Various Substrates.
Since water-thinned latex paints do not adhere well to chalky masonry surfaces, an oil-based conditioner is applied to the chalky substrate before latex paint is applied. The entire surface should be vigorously wire brushed by hand or power tools, then dusted to remove all loose particles and chalk residue. The conditioner is then brushed on freely to assure effective penetration and allowed to dry. Conditioner is not intended for use as a finish coat.
Sealers are applied to bare wood like coats of paint. Freshly exuded resin, while still soft, may be scraped off with a putty knife and the area cleaned with alcohol. Remove hardened resin by scraping or sanding. Since sealer is not intended as a prime coat, it should be used only when necessary and applied only over the affected area. When previous paint becomes discolored over knots on pine lumber, the sealer should be applied over the old paint before the new paint is applied.
Fillers are used on porous wood, concrete, and masonry to provide a smoother finish coat.
Wood fillers are used on open grained hardwoods. In general, hardwoods with pores larger than those found in birch should be filled. Table 6 lists the characteristics of various woods and which ones require fillers. The table also contains notes on finishing. Filling is done after staining. Stain should be allowed to dry for 24 hours before the filler is applied. If staining is not warranted, natural (uncolored) filler is applied directly to the bare wood. The filler may be colored with some of the stain to accentuate the grain pattern of the wood.
Table 6 – Characteristics of Wood.
To apply, you first thin the filler with mineral spirits to a creamy consistency, and then liberally brush it across the grain, followed by a light brushing along the grain. Allow it to stand 5 to 10 minutes until most of the thinner has evaporated. At this time, the finish will have lost its glossy appearance. Before it has a chance to set and harden, wipe the filler off across the grain using burlap or other coarse cloth, rubbing the filler into the pores of the wood while removing the excess. Finish by stroking along the grain with clean rags. All excess filler must be removed.
Knowing when to start wiping is important. Wiping too soon pulls the filler out of the pores. Allowing the filler to set too long makes it hard to wipe off. A simple test for dryness consists of rubbing a finger across the surface. If a ball is formed, it’s time to wipe. If the filler slips under the pressure of the finger, it is still too wet for wiping. Allow the filler to dry for 24 hours before applying finish coats.
Masonry fillers are applied by brush to bare and previously prepared (all loose, powdery, flaking material removed) rough concrete, concrete block, stucco, or other masonry surfaces. The purpose is to fill the open pores in the surface, producing a fairly smooth finish. If the voids on the surface are large, you should apply two coats of filler, rather than one heavy coat. This avoids mud cracking. Allow 1 to 2 hours drying time between coats. Allow the final coat to dry 24 hours before painting.
Most paints are ready-mixed, meaning the ingredients are already combined in the proper proportions. When oil paint is left in storage for long periods of time, the pigments settle to the bottom. These must be remixed into the vehicle before the paint is used. The paint is then strained, if necessary. All paint should be placed in the paint shop at least 24 hours before use. This is to bring the paint to a temperature between 65°F and 85°F. There are three main reasons to condition and mix paint. First, you need to re-disperse, or re-blend, settled pigment with the vehicle. Second, lumps, skins, or other impediments to proper application need to be eliminated. And, third, the paint must be brought to its proper application temperature.
Paints should be mixed, or blended, in the paint shop just before they are issued. Mixing procedures vary among different types of paints. Regardless of the procedure used, try not to overmix; this introduces too much air into the mixture. Table 7 outlines the types of equipment and remarks for various coatings.
Table 7 – Mixing
Mixing is done by either a manual or mechanical method. The latter is definitely preferred to ensure maximum uniformity. Manual mixing is less efficient than mechanical in terms of time, effort, and results. It should be done only when absolutely necessary and be limited to containers no larger than 1 gallon. Nevertheless, it is possible to mix 1 gallon and 5 gallon containers by hand. To do so, first pour half of the paint vehicle into a clean, empty container. Stir the paint pigment that has settled to the bottom of the container into the remaining paint vehicle. Continue to stir the paint as you return the other half slowly to its original container. Stir and pour the paint from can to can. This process of mixing is called boxing paint. The mixed paint must have a completely blended appearance with no evidence of varicolored swirls at the top. Neither should there be lumps of undispersed solids or foreign matter. Figure 88 illustrates the basic steps for boxing paint.
Figure 88 – Manual mixing and boxing of paint.
There are only three primary true pigmented colors: red, blue, and yellow. Shades, tints, and hues are derived by mixing these colors in various proportions. Figure 89 shows a color triangle with one primary color at each of its points.
Figure 89 – A color triangle.
The lettering in the triangle indicates the hues that result when colors are mixed.
A - Equal proportions of red and blue produce purple.
B - Equal proportions of red and yellow produce orange.
C - Equal proportions of blue and yellow produce green.
D - Three parts of red to one part of blue produce carmine.
E - Three parts of red to one part of yellow produce reddish orange.
F - Three parts of blue to one part of red produce red-violet.
G - Three parts of yellow to one part of red produce yellowish orange.
H - Three parts of blue to one part of yellow produce bluish green.
I - Three parts of yellow to one part of blue produce yellowish green.
Hues are known as chromatic colors, whereas black, white, and gray are achromatic (neutral) colors. Gray can be produced by mixing black and white in different proportions.
When received, paints should be ready for application by brush or roller. Thinner can be added for either method of application, but the supervisor or inspector must give prior approval. Thinning is often required for spray application. Unnecessary or excessive thinning causes an inadequate thickness of the applied coating and adversely affects coating longevity and protective qualities. When necessary, thinning is done by competent personnel using only the thinning agents named by the specifications or label instructions. Thinning is not done to make it easier to brush or roll cold paint materials. They should be preconditioned (warmed) to bring them up to 65°F to 85°F.
Normally, paint in freshly opened containers does not require straining. But in cases where lumps, color flecks, or foreign matter are evident, paints should be strained after mixing. When paint is to be sprayed, it must be strained to avoid clogging the spray gun.
Skins should be removed from the paint before mixing. If necessary, the next step is thinning. Finally, the paint is strained through a fine sieve or commercial paint strainer.
Try not to tint paint. This will reduce waste and eliminate the problem of matching special colors at a later date. Tinting also affects the properties of the paint, often reducing performances to some extent. One exception is the tinting of an intermediate coat to differentiate between that coat and a top coat; this helps assure you don’t miss any areas. In this case, use only colorants of known compatibility. Try not to add more than 4 ounces of tint per gallon of paint. If more is added, the paint may not dry well or otherwise may perform poorly.
When necessary, tinting should be done in the paint shop by experienced personnel. The paint must be at application viscosity before tinting. Colorants must be compatible, fresh, and fluid to mix readily. Mechanical agitation helps distribute the colorants uniformly throughout the paint.
The common methods of applying paint are brushing, rolling, and spraying. The choice of method is based on several factors, such as speed of application, environment, type and amount of surface, type of coating to be applied, desired appearance of finish, and the training and experience of the painters. Brushing is the slowest method, rolling is much faster, and spraying is usually the fastest by far. Brushing is ideal for small surfaces and odd shapes or for cutting in corners and edges. Rolling and spraying are efficient on large, flat surfaces. Spraying can also be used for round or irregular shapes.
Local surroundings may prohibit the spraying of paint because of fire hazards or potential damage from over spraying, or accidentally getting paint on adjacent surfaces. When necessary, adjacent areas not to be coated must be covered when spraying is performed. This results in loss of time and, if extensive, may offset the speed advantage of spraying.
Brushing may leave brush marks after the paint is dry. Rolling leaves a stippled effect. Spraying yields the smoothest finish, if done properly. Lacquer products, such as vinyls, dry rapidly and should be sprayed. Applying them by brush or roller may be difficult, especially in warm weather or outdoors on breezy days. The painting method requiring the most training is spraying. Rolling requires the least training.
A coating that prematurely reaches the end of its useful life is said to have failed. Even protective coatings properly selected and applied on well prepared surfaces gradually deteriorate and eventually fail. The speed of deterioration under such conditions is less than when improper painting procedures are earned out. Inspectors and personnel responsible for maintenance painting must recognize signs of deterioration to establish an effective and efficient system of inspection and programmed painting. Repainting at the proper time avoids the problems resulting from painting either too soon or too late. Applying coatings ahead of schedule is costly and eventually results in a heavy buildup that tends to quicken deterioration of the coating. Applying a coating after it is scheduled results in costly surface preparation and may be responsible for damage to the structure, which may then require expensive repairs.
In the following sections, we’ll look at some of the more common types of paint failures, the reasons for such failures, methods of prevention, and cures.
Figure 90 – Alligatoring.
Paint failures can result from many causes. Here we will look at some of the most common, which result from faults in surface preparation.
Alligatoring, shown in Figure 90, refers to a coating pattern that looks like the hide of an alligator. It is caused by uneven expansion and contraction of the undercoat. Alligatoring can have several causes: applying an enamel over an oil primer; painting over bituminous paint, asphalt, pitch, or shellac; and painting over grease or wax.
Figure 91 – Peeling.
Peeling, shown in Figure 91, results from inadequate bonding of the topcoat with the undercoat or the underlying surface. It is nearly always caused by inadequate surface preparation. A topcoat peels when applied to a wet, dirty, oily or waxy, or glossy surface. All glossy surfaces must be sanded before painting. Also, the use of incompatible paints can cause the loss of adhesion. The stresses in the hardening film can then cause the two coatings to separate and the topcoat to flake and peel.
Figure 92 – Blistering.
Blistering is caused by the development of gas or liquid pressure under the paint. Examples are shown in Figure 92. The root cause of most blistering, other than that caused by excessive heat, is inadequate ventilation plus some structural defect allowing moisture to accumulate under the paint. A prime source of this problem is the use of essentially porous major construction materials that allow moisture to pass through. Insufficient drying time between coats is another prime reason for blistering. All blisters should be scraped off, the paint edges feathered with sandpaper, and the bare places primed before the blistered area is repainted.
Prolonged Tackiness – A coat of paint is dry when it ceases to be tacky to the touch. Prolonged tackiness indicates excessively slow drying. This may be caused by insufficient drier in the paint; a low quality vehicle in the paint; applying the paint too thickly; painting over an undercoat that is not thoroughly dry; painting over a waxy, oily, or greasy surface; or painting in damp weather.
Inadequate Gloss – Sometimes a glossy paint fails to attain the normal amount of gloss. This may be caused by inadequate surface preparation, application over an undercoat that is not thoroughly dry, or application in cold or damp weather.
One particular area you, as a Builder, have direct control over is application. It takes a lot of practice, but you should be able to eliminate the two most common types of application defects, crawling and wrinkling.
Crawling, shown in Figure 93, is the failure of a new coat of paint to wet and form a continuous film over the preceding coat. This often happens when latex paint is applied over high gloss enamel or when paints are applied on concrete or masonry treated with silicone water- repellent.
Figure 93 – Crawling.
When coatings are applied too thickly, especially in cold weather, the surface of the coat dries to a skin over a layer of undried paint underneath. This usually causes wrinkling, shown in Figure 94. Wrinkling can be avoided in brush painting or roller painting by brushing or rolling each coat of paint as thinly as possible. In spray painting, you can avoid wrinkling by keeping the gun in constant motion over the surface whenever the trigger is down.
Figure 94 – Wrinkling.
Not all painting defects are caused by the individual doing the job. It sometimes happens that the coating itself is at fault. Chalking, checking, and cracking are the most common types of product defects you will notice in your work as a Builder.
Figure 95 – Degrees of chalking.
Chalking, shown in Figure 95, is the result of paint weathering at the surface of the coating. The vehicle is broken down by sunlight and other destructive forces, leaving behind loose, powdery pigment that can easily be rubbed off with the finger. This gradual wearing away reduces the thickness of the coating, which means the surface can be painted repeatedly without making the coating too thick for satisfactory service.
Chalking takes place rapidly with soft paints, such as those based on linseed oil. Chalking is most rapid in areas exposed to sunshine. In the Northern Hemisphere, for example, chalking is most rapid on the south side of a building. On the other hand, little chalking takes place in areas protected from sunshine and rain, such as under eaves or overhangs. Controlled chalking can be an asset, especially in white paints where it acts as a self-cleaning process and helps to keep the surface clean and white.
Do not use a chalking or self-cleaning paint above natural brick or other porous masonry surfaces. The chalking will wash down and stain or discolor these areas.
Chalked paints are generally easier to repaint since the underlying paint is in good condition and requires little surface preparation. But this is not the case with water-thinned paints, which adhere poorly to chalky surfaces.
Checking and cracking are breaks in a coating formed as the paint becomes hard and brittle. Temperature changes cause the substrate and overlying paint to expand and contract. As the paint becomes hard, it gradually loses its ability to expand without breaking. Checking, shown in Figure 96, consists of tiny breaks in only the upper coat or coats of the paint film without penetrating to the substrate. The pattern is usually similar to that of a crow’s foot.
Figure 96 – Severe checking.
Cracking is larger with longer breaks extending through to the substrate, as shown in Figure 97. Both result from stresses exceeding the strength of the coating. But, whereas checking arises from stress within the paint film, cracking is caused by stresses between the film and the substrate.
Figure 97 – Severe cracking.
Cracking generally takes place to a greater extent on wood, due to its grain, than on other substrates. The stress in the coating is greatest across the grain, causing cracks to form parallel to the grain of the wood. Checking and cracking are aggravated by excessively thick coatings that have reduced elasticity. Temperature variations, humidity, and rainfall are also concerns for checking or cracking.
There are three destructive forces against which most wood protective measures are directed: biological deterioration where wood is attacked by any of a number of organisms, fire, and physical damage. In this section, we will deal with protecting wood products against biological deterioration.
Damage to wood buildings and other structures by termites, wood bores, and fungi is a needless waste. The ability of wood to resist such damage can be greatly increased by proper treatment and continued maintenance. Wood defects are also caused by **98 improper care after preservation treatment. All surfaces of treated wood that are cut or drilled to expose the untreated interior must be treated with a wood preservative.
There are two basic methods for treating wood, pressure and non-pressure. Pressure treatment is superior to nonpressure, but costly and time consuming. Building specifications dictate which method to use.
Pressure – The capacity of any wood to resist dry rot, termites, and decay can be greatly increased by impregnating the wood with a general purpose wood preservative or fungicide. It is important to remember that good pressure treatment adds to the service life of wood in contact with damp ground. It does not, however, guarantee the wood will remain serviceable throughout the life of the building it supports.
Woods of different timber species do not treat with equal ease. Different woods have different capacities for absorbing preservatives or other liquids. In any given wood, sapwood is more absorbent than heartwood. Hardwoods are, in general, less absorbent than softwoods. Naturally, the extent to which a preservative protects increases directly with the depth it penetrates below the surface of the wood. As just mentioned, the best penetration is obtained by a pressure method.
Table 8 shows the ease of preservative penetration into various woods. In the table, E = easy, M = moderate, and D = difficult.
Table 8 – Preservative Penetration.
Nonpressure – Nonpressure methods of applying preservatives to a surface include dipping, brushing, and spraying. Figure 98 shows how you can improvise long tanks for the dipping method. Absorption is rapid at first, then much slower. A rule of thumb holds that in 3 minutes wood absorbs half the total amount of preservative it will absorb in 2 hours. The extent of the penetration depends upon the type of wood, its moisture content, and the length of time it remains immersed.
Figure 98 – Improvised tanks for dip treating lumber.
Surface application by brush or spray is the least satisfactory method of treating wood from the standpoint of maximum penetration. It is more or less unavoidable in the case of already installed wood as well as treated wood that has been cut or drilled to expose the untreated interior.
Pentachlorophenol and creosote coal tar are likely to be the only field-mixed preservatives used by the Builder. The type of treatment or preservative depends on the severity of exposure and the desired life of the end product. Preservatives can be harmful to personnel if improperly handled. When applying preservatives, you should take the following precautions:
Every painting assignment exposes Builders to conditions and situations representing actual or potential danger. Toxic and flammable materials, pressurized equipment, ladders, scaffolding, and rigging always make painting a hazardous job. Hazards may also be inherent in the very nature of the environment, or result from ignorance or carelessness by the painter.
The main causes of painting accidents are unsafe working conditions or equipment, and careless personnel. The proper setting up and dismantling of equipment, the required safety checks, and the proper care of equipment may require more time than is spent using it. Nevertheless, safety measures must be taken.
Certain general rules regarding fire and explosion hazards apply to all situations. All paint materials should have complete label instructions stipulating the potential fire hazards and precautions to be taken. Painters must be advised and reminded of the fire hazards that exist under the particular conditions of each job. They need to be aware of the dangers involved and the need to work safely. Proper firefighting equipment must always be readily available in the paint shop, spray room, and other work areas where potential fire hazards exist. Electric wiring and equipment installed or used in the paint shop, including the storage room and spray room, must conform to the applicable requirements of the National Electrical Code (NEC) for hazardous areas.
Many poisons, classified as toxic and skin-irritating, are used in the manufacture of paint. Although your body can withstand small quantities of poisons for short periods, overexposure can have harmful effects. Continued exposure to even small amounts may cause the body to become sensitized; subsequent contact, even in small amounts, may cause an aggravated reaction. The poisons in paint are definite threats to normally healthy individuals and serious dangers to persons having chronic illnesses or disorders. Health hazards can be avoided by a common sense approach of avoiding unnecessary contact with toxic or skin-imitating materials.
As with all tasks a builder undertakes, safety must be a primary concern from the earliest planning stages to the final cleanup. Shortcuts, from personnel protection to equipment-related safety devices, should not be permitted. Follow the project safety plan, and consult all applicable safety manuals when involved with any paint operation. Remember: work safe, stay safe.
Test your Knowledge
10. Which of the following paint ingredients acts as the binder?
- A. Pigment
- B. Drier
- C. Vehicle
- D. Thinner
11. During the paint-mixing process, what is meant by boxing the paint?
- A. Pouring it back and forth from one container to another
- B. Mixing it with a mechanical agitator
- C. Mixing it with a paddle
- D. Cutting it with a suitable thinner
12. What is the recommended maximum amount of tint for one gallon of paint?
- A. 1 ounce
- B. 2 ounces
- C. 3 ounces
- D. 4 ounces.
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Paneling is another form of interior finish that you might encounter. Types of paneling include plywood, hardboard, plastic laminates, and solid lumber paneling.
Most of the plywood used for interior walls has a factory-applied finish that is tough and durable. Manufacturers can furnish prefinished matching trim and molding that is also easy to apply. Color coordinated putty sticks are used to conceal nail holes.
Joints between plywood sheets can be treated in a number of ways. Some panels are fabricated with machine shaped edges that permit almost perfect joint concealment. Usually it is easier to accentuate the joints with grooves or use battens and strips. Some of the many different styles of battens are shown in Figure 99.
Figure 99 – Battens used for paneling joints.
Before installation, the panels should become adjusted (conditioned) to the temperature and humidity of the room. Carefully remove prefinished plywood from cartons and stack it horizontally. Place 1 inch spacer strips between each pair of face to face panels. Do this at least 48 hours before application.
Plan the layout carefully to reduce the amount of cutting and the number of joints. It is important to align panels with openings whenever possible. If finished panels are to have a grain, stand the panels around the walls and shift them until you have the most pleasing effect in color and grain patterns. To avoid mix-ups, number the panels in sequence after their position has been established. When you cut plywood panels with a portable saw, mark the layout on the back side. Support the panel carefully and check for clearance below. Cut with the saw blade upward against the panel face. This minimizes splintering. This procedure is even more important when working with prefinished panels.
Plywood can be attached directly to the wall studs with nails or special adhesives. Use 3/8 inch plywood for this type of installation. When studs are poorly aligned or when the installation is made over an existing surface in poor condition, it is usually advisable to use furring. Nail 1 by 3 or 1 by 4 inch furring strips horizontally across the studs. Start at the floor line and continue up the wall. Spacing depends on the panel thickness. Thin panels need more support. Install vertical strips every 4 feet to support panel edges. Level uneven areas by installing shimmies behind the furring strips. Prefinished plywood panels can be installed with special adhesive. The adhesive is applied and the panels are simply pressed into place; no sustained pressure is required.
Begin installing panels at a corner. Scribe and trim the edges of the first panel so it is plumb. Fasten it in place before fitting the next panel. Allow approximately 1/4 inch clearance at the top and bottom. After all panels are in place, use molding to cover the space along the ceiling. Use baseboards to conceal the space at the floor line. If the molding strips, baseboards, and strips used to conceal panel joints are not prefinished, they should be spray painted or stained a color close to the tones in the paneling before installation.
On some jobs, 1/4 inch plywood is installed over a base of 1/2 inch gypsum wallboard. This backing is recommended for several reasons. It tends to bring the studs into alignment. It provides a rigid finished surface. It improves the fire-resistant qualities of the wall. The plywood is bonded to the gypsum board with a compatible adhesive.
Through special processing, hardboard, also called fiberboard, can be fabricated with a very low moisture absorption rate. This type is often scored to form a tile pattern. Panels for wall application are usually 1/4 inch thick.
Since hardboard is made from wood fibers, the panels expand and contract slightly with changes in humidity. They should be installed when they are at their maximum size. The panels tend to buckle between the studs or attachment points if installed when moisture content is low. Manufacturers of prefinished hardboard panels recommend that they be unwrapped and placed separately around the room for at least 48 hours before application.
Procedures and attachment methods for hardboard are similar to those for plywood. Special adhesives are available as well as metal or plastic molding in matching colors. You should probably drill nail holes for the harder types.
Plastic laminates are sheets of synthetic material that are hard, smooth, and highly resistant to scratching and wear. Although basically designed for table and countertops, they are also used for wainscoting and wall paneling in buildings.
Since plastic laminate material is thin, 1/32 to 1/16 inch, it must be bonded to other supporting panels. Contact bond cement is commonly used for this purpose. Manufacturers have recently developed prefabricated panels with the plastic laminate already bonded to a base or backer material. This base consists of a 1/32 inch plastic laminate mounted on 3/8 inch particleboard. Edges are tongue and grooved so that units can be blind nailed into place. Various matching corner and trim moldings are available.
Solid wood paneling makes a durable and attractive interior wall surface and may be appropriately used in nearly any type of room. Several species of hardwood and softwood are available. Sometimes grades with numerous knots are used to obtain a special appearance. Defects, such as the deep fissures in pecky cypress, can also provide a dramatic effect.
The softwood species most commonly used include pine, spruce, hemlock and western red cedar. Boards range in widths from 4 to 12 inches nominal size and are dressed to 3/4 inch. Board and batten or shiplap joints are sometimes used, but tongue and groove (T&G) joints combined with shaped edges and surfaces are more popular.
When solid wood paneling is applied horizontally, furring strips are not required; the boards are nailed directly to the studs. Inside corners are formed by butting the paneling units flush with the other walls. If random widths are used, boards on adjacent walls must match and be accurately aligned.
Vertical installations require furring strips at the top and bottom of the wall and at various intermediate spaces. Sometimes 2 by 4 inch blocking is installed between the studs to serve as a nailing base, as shown in Figure 100. Even when heavy T&G boards are used, these nailing members should not be spaced more than 24 inches apart.
Figure 100 – Vertical wood paneling.
Narrow widths (4 to 6 inches) of T&G paneling are blind nailed. The nail heads do not appear on finished surfaces, and you eliminate the need for countersinking and filling nail holes. This nailing method also provides a smooth, blemish-free surface. This is especially important when clear finishes are used. Drive 6d finishing nails at a 45° angle into the base of the tongue and on into the bearing point. Carefully plumb the first piece installed and check for the plumbness at regular intervals. For lumber paneling that is not tongue and groove, use 6d casing or finishing nails. Use two nails at each nailing member for panels 6 inches or less in width and three nails for wider panels.
Exterior wall constructions, where the interior surface consists of solid wood paneling, should include a tight application of building paper located close to the backside of the boards. This prevents the infiltration of wind and dust through the joints. In cold climates, insulation and vapor barriers are important. Base, corner, and ceiling trim can be used for decorative purposes or to conceal irregularities in joints.
Test your Knowledge
13. The degree of protection provided to wood by a wood preservative depends on which of the following conditions?
- A. The type of wood only
- B. The moisture content of the wood only
- C. The length of time the wood is treated only
- D. All of the above
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In this course you learned about the finishes that make a building durable, habitable, and pleasing to look at. You learned about topics ranging from exterior finishes and trim to interior wall finishes, including drywall, plaster, ceramic tile, paint, and paneling. You also learned about acoustic ceilings and various floor finishes, including wood flooring, resilient flooring, and carpeting. You learned that many of the installations described in this course include the use of hazardous materials, which need to be handled with care to ensure the safety of the crew.
1. For exterior trim fasteners, which of the following types of screws or nails is/are preferred?
2. What part of a gable roof projects beyond the end wall on an upward slope?
3. On a roof with no overhang, what type of cornice is normally used?
4. In closed cornice construction, the underside of the eaves is exposed.
5. Which of the following components provides a nailing base for soffit material?
6. Wood soffit panels should be fastened using nails in what (a) size and (b) spacing?
7. In drywall construction, nail pops result from which of the following factors?
8. To align ceiling joists in an unfinished attic, what type of structural member should you use?
9. The most common size gypsum board has what (a) thickness and (b) type edges?
10. What type of drywall is also called greenboard or blueboard?
11. What type of drywall edge(s) may be left exposed?
12. When studs are spaced 24 inches OC, what thickness of drywall is recommended for quality wall construction?
13. What is the best reason for using a convex head hammer when driving drywall nails?
14. For the best drywall finish, you should apply the topping coat with which of the following drywall tools?
15. What length of smooth shanked nail should be used when installing double layers of 1/2 inch drywall?
16. What minimum length type W screw should you use when installing 1/2 inch drywall to wood studs?
17. Which of the following metal beads is installed to protect drywall from edge damage?
18. Single nailed drywall should be installed with what OC nail spacing on the (a) walls and (b) ceiling?
19. After the first application of joint compound to a joint, what should be the next step?
20. Select from the following list the proper sequence for taping a gypsum drywall joint. a. Apply a coat of joint compound to bury tape. b. Press tape into center of joint. c. Allow compound to dry. d. Sand edges. e. Spread a bed of joint compound about 4 inches wide.
21. When you are repairing gypsum drywall, holes larger than what minimum diameter in inches should be cut back to the center of the nearest studs?
22. Which of the following plaster binding materials should NOT be exposed to severe moisture?
23. Which of the following statements best describes gypsum gauging plaster?
24. Gauging material is added to lime plaster for which of the following reasons?
25. Portland cement plaster should NOT be applied directly over what type of walls?
26. When the aggregate material is excessively fine grain, why is the plaster strength reduced?
27. Which of the following aggregates should be used in acoustical plaster?
28. To provide a good key, wood lath plaster base should have what minimum spacing?
29. What is the main purpose of the 3/4 inch holes in perforated gypsum lath?
30. What type of lath is considered the most versatile?
31. What length of blued gypsum lath nail is recommended for installing 1/2 inch gypsum lath?
32. What is the minimum end lap for wire lath?
3. What is the purpose of a casing bead?
34. To minimize shrinking and cracking around the upper corners of doors and windows, you should install which of the following items?
35. What are the recommended material and proportions for two-coat plaster used on a masonry or concrete base?
36. You should not apply a lime finish to which of the following base coats?
37. When mortar materials are mixed by hand, what is the maximum time in minutes that mixing should continue after all the materials have been blended?
38. After all ingredients for plaster have been added, what minimum time in minutes should a mixing machine be allowed to mix?
9. Normally, what is the specified flatness tolerance of a plastered surface?
40. What tool is used for carrying mortar?
41. To improve adhesive bonds, what tool should be used to make furrows between coats?
42. On a typical plastering crew, which of the following individuals normally mixes the plaster?
43. Which of the following statements is applicable to the fog spray curing of Portland cement plaster?
44. Throwing plaster on a surface with a brush produces which of the following textures?
45. Which of the following statements best defines stucco?
46. When using an acid wash to prepare a concrete surface for stucco, you should use one part acid to how many parts of water?
47. Which of the following factors is most likely to cause discoloration in a stucco finish coat?
48. How many basic ceramic tile installation methods are there?
49. What is the minimum soaking time for tile when using the cement mortar installation method?
50. Which of the following types of grout should be used when sanitation is important?
51. How many parts of hydrated lime and sand should be used with three parts of cement for a float coat of a mortar bed setting for ceramic tile?
52. Most acoustical ceilings have what main purpose?
53. Assume the dimensions of a ceiling are 16 feet 8 inches by 10 feet 2 inches. When calculating the material requirements, what dimensions should you use?
54. Assume you are laying out the grid pattern for a ceiling. How should the main tees run?
55. Assume a new acoustical ceiling will be installed 14 inches lower than the old ceiling. The suspension wires should be cut with what minimum length in inches?
56. In a suspension ceiling system, where on the main tee should the first tie wire be installed?
57. When installed, which of the following components require the use of splice plates?
58. When installing acoustical panels, why should you work from several cartons at the same time?
59. When installing 12 inch square ceiling tile in a 15 foot 8 inch-wide room, what pattern should you use in terms of rows and size?
60. Subfloor boards are normally laid over joists in what direction?
61. Building paper is used over subfloors to reduce which of these?
62. At which of the following angles should nails be driven through the tongue of tongue and groove flooring?
63. How can you prevent splitting the tongue when nailing tongue and groove flooring?
64. A vapor barrier is installed under a concrete slab before it is poured. Is any further preparation required for the later installation of wood flooring?
65. What is the expansion allowance for hardboard underlayment when laid next to a vertical surface?
66. Nail spacing for 1/2 inch plywood underlayment should not exceed what OC (a) edge and (b) field spacing?
67. Before laying vinyl tile on a floor surface, you should square off the floor, apply the adhesive, and then begin laying the tile from which of these directions?
68. Which of the following factors is an advantage of using carpeting instead of other types of floor covering?
69. When installing cushion-backed carpeting, which of the following items is/are required?
70. In paint, which of the following ingredients provides the coloring?
71. Which of the following chemical compounds are NOT synthetic resins?
72. What is the purpose of a paint solvent?
73. To increase resistance of oil-base paint to water and decrease drying time, you should add small amounts of what material to the paint?
74. Which of the following ratios determines the level of gloss in enamel paints?
75. Of the following paint types, which is best suited to masonry surfaces?
76. In areas that require frequent washing, which of the following types of paint is normally preferable?
77. When a can of ready-mix aluminum paint is bulging, how should the pressure be released?
78. Which of the following materials does NOT obscure the surface to which it is applied?
79. Which of the following types of varnish is intended for exterior use?
80. Which of the following materials is often used as a sealant over wood knots to prevent bleeding?
81. What type of stain contains alcohol as a vehicle?
82. Which of the following advantages is gained by proper surface preparation?
83. You should prepare a galvanized iron surface for painting with which of the following types of cleaners?
84. Dirt and fungus are best removed from concrete and masonry by washing with which of the following types of solutions?
85. During the process of removing efflorescence from concrete, what should you do after scrubbing with an acid solution?
86. What is the correct procedure for mixing muriatic acid and water?
87. To repair large defects in a concrete or masonry surface, which of the following grout mixtures should you use?
88. Before painting, a plaster patch should set for what minimum time?
90. Before painting, what is the procedure for sanding a rough wood surface?
91. When used on porous wood, concrete, and masonry, which of the following items produces a smooth finish floor coat?
92. When applied to chalky bases, which of the following items improves adhesion of water-based paints?
93. Which of the following items prevents resin from bleeding through applied paint coatings?
94. Before applying filler to open grained wood, stain should be applied and allowed to dry for how many hours?
95. Before varnishing, you should use a filler on which of the following open grained woods?
96. To mix two-package metallic paints, what method is recommended?
97. What are the three primary or true colors that are the basis for all subsequent shades, tints, and hues?
98. Before its application by roller, a ready-mix paint must be thinned.
99. Strong sunlight on paint surfaces is most likely to cause which of the following problems?
100. Inadequate bonding and what other cause are the primary reasons for peeling?
101. Temperature changes causing the substrate and overlaying paint film to expand and contract are most likely to result in which of the following conditions?
102. Accumulation of moisture under paint is most likely to cause which of the following problems?
103. Breaks in paint film extending through to the substrate indicate what type of paint failure?
104. Spraying paint too thickly or moving the spray gun too slowly is most likely to cause which of the failing paint failures?
105. Failure of a gloss paint to attain its normal gloss is most likely to be caused by which of the following conditions?
106. What is the recommended minimum thickness of plywood panels used directly over framing members?
107. When you are installing vertical board panels, what is the maximum spacing in inches of furring strips?
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Copyright David L Heiserman
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