Essentials of
Masonry

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Part 2--Construct a Concrete-Block Wall

CONTROL JOINTS

Control joints are continuous vertical joints that are built into concrete-blocks walls to control cracking from unusual stress. They are usually spaced at 20- to 25-foot intervals in long walls and extend to the top course. A wall shorter than 20 feet does not normally require a control joint.

2-12. Using Full- and Half-length Blocks. Use full- and half-length blocks to form a continuous vertical joint which will permit slight wall movement without cracking. You should lay control joints up in mortar just like any other joint (Figure 2-11).

Figure 2-11.  A control joint using full- and half-length blocks
Figure 2-11. A control joint using full- and half-length blocks

2-13. Using Paper and Felt. You can make another type of control joint by inserting building paper or roofing felt in the end core of the block and extending it the full length of the control joint. Cut the paper or felt to convenient lengths. Make sure it is wide enough to extend across the joint to prevent the mortar from bonding on one side of the joint (Figure 2-12).

Figure 2-12.  Control joints using paper or felt
Figure 2-12. Control joints using paper or felt

2-14. Caulking. If the control joints are exposed to the weather or to view, you should caulk them. When the mortar in the control joint is stiff, rake it out to a depth of 3/4 inch to provide a recess for the caulking materials (Figure 2-13). Use a thin, flat caulking trowel to force the caulking compound into the joint.

Figure 2-13.  Raking mortar from the joints
Figure 2-13. Raking mortar from the joints

David L. Heiserman, Editor

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Revised: June 06, 2015