When replacing a horizontal band of masonry either for a flashing or angle repair, how can you ensure that the top joint of the new masonry is adequately filled?
To ensure that the top joint is filled properly, you should make certain it is wide enough, take special care when filling it, and verify that it is filled at randomly selected locations. The joint should be 3/8-inch wide to permit mortar to be packed into the joint. It is essential to repoint the joint full depth in 1/4- to 3/8-inch-deep layers in order to ensure adequate filling. I know one contractor that uses a backer rod in the back of the joint so that the first layer of mortar can be pressed against the backer rod. Other contractors have used a trowel to put mortar on the upper and lower portions of the brick at the back of the joint, then packed the joint starting from that point outward. To verify that the mortar joint has been filled adequately, you can drill a hole to determine the depth of the mortar in the joint and whether any voids are present. The diameter of the drill bit should be at least 1/8-inch less than the width of the joint, and the hole should be drilled in the center of the joint. Test holes then can be filled with mortar by grinding out and pointing the outer three-quarters of the joint; or they can be filled with sealant and dusted on the surface with mortar. It is difficult to fill a 1/4-inch hole with mortar alone.