The mortar joints in a masonry wall, whether brick, concrete block, or stone, serve two purposes: the mortar joints serve to bind the masonry units together for structural strength, and they provide a watertight seal between the masonry units. Over time, the mortar can deteriorate and begin to crumble and fall out, resulting in gaps, weak walls, and unsightly surfaces. The vertical masonry joints are known as head joints, and the horizontal masonry joints are known as bed joints.
To begin tuckpointing mortar joints, the loose and deteriorated mortar must first be removed. Several methods may be used, including hammer and chisel, or power saws with masonry blades. Care must be taken to protect the masonry units from cracking, chipping, or saw cuts, as these will cause further harm to the wall in the future. Make sure that the old mortar has been completely removed. Inspect the joints for loose stones, and use an air compressor to blow out the remaining stones, dust, and dirt.
Prepare the joints by first saturating the masonry with clear water using a sprayer to thoroughly wet all surfaces inside the joints. If this step is not taken, the masonry will absorb moisture from the new mortar, and the loss of water will weaken the final joint. There should be no standing water in the joints after saturating the surfaces. If there is, use compressed air to blow out the free water. Allow the surfaces to dry slightly and repeat the process if the water is absorbed quickly.
Mortar should be mixed in small batches. For old bricks and stones, use mortar composed of one part Portland cement, one part hydrated lime, and three parts fine sand. For modern bricks and concrete masonry, use mortar composed of one part Portland cement, one part masonry cement, and 2.5 parts fine sand. For both types of mortar, use just enough water to thoroughly saturate the ingredients. The finished mortar should be pliable and able to cling to a vertical wood board.
Using a pointing tool, begin pressing small amounts of mortar into the joint, completely filling the joint and packed tightly, tucking it into the voids of the joint. A completely tucked joint should be packed to the exterior surface of the surrounding masonry.
After about an hour, when the mortar has begun to set, use a curved jointing tool to rake the joints to a smooth concave surface that is tight and waterproof.