Question: Why is three-wire bed-joint reinforcement used with brick cavity walls with concrete masonry backups? Isn't the brick tied adequately merely by having the wires at the inner and outer portions of the wall?

Answer: The three wires in this joint reinforcement are used when concrete masonry is used as the backup. Two wires are positioned in the bed joint of the concrete masonry wythe to control shrinkage cracking. The wires should be positioned in the center portions of both the front and back face shells of the concrete masonry backup wall. In this way, the joint reinforcement actually serves two functions: it connects the outer wythe to the backup wythe and reinforces the concrete masonry for crack control resulting from shrinkage.