Is applying regular pointing mortar over the surface of bad joints an effective way to reduce water leakage through the masonry?
Not as a long-term solution. If only the joints with separations are to be corrected, the laborer or pointer must identify the vulnerable joints. Some readily identified separations may extend only a short distance into the joint. Others, which appear smaller on the surface, may penetrate entirely through the thickness of the wall and may actually be more of a problem. Applying standard mortar over the face of the existing joint is not a durable repair. Instead of having 3/4-inch contact with the brick, the feathered edge of the mortar smear may have almost no contact at all. The portion of the new mortar which contacts the brick may readily weather. Also, if any movement occurs at all, the separation will readily reopen, because little bond has been achieved. In many cases, joints may be repaired by applying a very fine grout mixture over the face of the joint. Several proprietary grout mixes are available for this use. The Brick Institute of America in Technical Notes 7F recommends using a mixture of 1 part portland cement, 1/3 part hydrated lime and 1 1/3 parts fine sand passing a No. 30 sieve. In this method, the mixture must be forced into separations at the joint interface with a stiff brush. Because grout is applied to the surface of the bricks, this method generally is used only on smooth-surfaced bricks so the grout can be brushed off when it's dry. Using a template or masking tape on more porous surfaces, though sometimes effective, may be very expensive.