How to Repair Mortar in a Brick Wall

Scrape out the horizontal joints to a depth of at least ¾ inch. (Joints wider than ½ inch have to be deeper: 2½ times the joint's width.) A carbide-tipped grout saw (below) works well on these ¼-inch-wide "butter joints." (On wider joints, use a cold chisel and an engineer's hammer.) Avoid electric angle grinders. Unless you’re trained to use them, they're almost guaranteed to cut into and disfigure the brick.