What causes concrete block walls to crack every 10 to 20 feet? What can I do to prevent this cracking?
Cracking can be caused by structural loading, displace- ment, or shrinkage. Regularly spaced cracks often are caused by shrinkage of the concrete block. The spacing of such shrinkage cracks depends on the moisture content of the block when installed, the amount of the block's linear shrinkage, and the humidity in the area where it is installed. The best way to control cracking is to install control joints at fairly close intervals throughout the wall. These control joints should be sealed. If properly installed, the sealant will then accommodate movement. Type I concrete masonry units can be used to minimize shrinkage. However, they often are difficult to obtain. At the site they must be carefully protected so they do not take on moisture. Bed joint reinforcement also can help control such cracking. NCMA-Tek 53, "Design of Concrete Masonry for Crack Control," gives control joint spacing requirements for walls with varying amounts of joint reinforcement. These are maximum spacing requirements. I recommend you consider closer spacing for greater protection against cracking.