Masonry Magazine December 2002 Page. 29
Joint reinforcement or bond beams can be used in conjunction to increase the tensile strength of the wall, whether laid in stacked bond or running bond patterns, thereby reducing the chances for cracks or limiting how much cracking actually occurs on the wall face.
"Control joints are for aesthetic and water penetration reasons," says Graber. "If it's an exterior wall and it's covered up with furring or something like that, they're just in there for aesthetic reasons. The shrinkage cracks don't inhibit the strength of the wall. "The idea of control joints is to give a place so those joints can open up to reduce the restraint and, in essence, it's putting in pre-formed cracks. It's just a weakened plane joint so that when it dries out and it cracks, it cracks in a nice straight line. The way you do that is you rake out the mortar joints, so that they're weaker there, then you put a backer rod and sealant in so that you don't get water penetration."
The elastomeric sealant should be one that remains flexible, like a silicone sealant, and doesn't become hard or rigid. It should meet ASTM C920 standards and be installed using ASTM C962. In exterior walls it is especially important to keep the seal weather-tight, so the sealant should have good contact with the edges. By keeping the sealant thicker on the edges and thinner in the middle, around the backer rod, the sealant will remain more flexible and allow for movement without tearing. In addition to the backer rod and sealant, a shear key with a gasket can be used in the joint for added load transfer. Joint reinforcement or bond beams can be used in conjunction to increase the tensile strength of the wall, whether laid in stacked bond or running bond patterns. Dowelled joints, although rarely used, can also be a way to transfer even higher loads at the joint.
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