Repair of Leaky Joints

Leakage of wind-driven rain through the joints in permeable brick masonry walls can be stopped by either repointing or grouting the joints. It is usually advisable to treat all the joints, both vertical and horizontal, in the wall face. Some tuckpointing operations in which only a few, obviously defective joints are treated may be inadequate and do not necessarily ensure that the untreated joints will not leak.
Repointing consists of cutting away and replacing the mortar from all joints to a depth of about 5⁄8 in. After the old mortar has been removed, the dust and dirt should be washed from the wall and the brick thoroughly wetted with water to near   saturation. While the masonry is still very damp but with no water showing, the  joints should be repointed with a suitable mortar. This mortar may have a somewhat stiff consistency to enable it to be tightly packed into place, and it may be prehydrated by standing for 1 or 2 hr before retempering and using. Pre-hydration is said to stabilize the plasticity and workability of the mortar and to reduce the shrinkage of the mortar after its application to the joints.

After repointing, the masonry should be kept in a damp condition for 2 or 3 days. If the brick are highly absorptive, they may contain a sufficient amount of water to aid materially in curing.
Weathering and permeability tests described in C. C. Fishburn, Effect of Outdoor Exposure on the Water Permeability of Masonry Walls, National Bureau of Standards BMS Report 76 indicate that repointing of the face joints in permeable brick masonry walls was the most effective and durable of all the remedial treatments against leakage that did not change the appearance of the masonry.
Joints are grouted by scrubbing a thin coating of a grout over the joints in the masonry. The grout may consist of equal parts by volume of portland cement and fine sand, the sand passing a No.30 sieve.
The masonry should be thoroughly wetted and in a damp condition when the grout is applied. The grout should be of the consistency of a heavy cream and should be scrubbed into the joints with a stiff bristle brush, particularly into the juncture between brick and mortar. The apparent width of the joint is slightly increased by some staining of the brick with grout at the joint line. Excess grout may be removed from smooth-textured brick with a damp sponge, before the grout hardens. Care should be taken not to remove grout from between the edges of the brick and the mortar joints. If the bricks are rough-textured, staining may be controlled by the use of a template or by masking the bricks with paper masking tape.
Bond of the grout to the joints is better for cut or flush joints than for tooled joints. If the joints have been tooled, they should preferably not be grouted until after sufficient weathering has occurred to remove the film of cementing materials from the joint surface, exposing the sand aggregate.
Grouting of the joints has been tried in the field and found to be effective on leaky brick walls. The treatment is not so durable and water-resistant as a repointing job but is much less expensive than repointing. Some tests of the water resistance of grouted joints in brick masonry test walls are described in National Bureau of Standards BMS Report 76.
The cost of either repointing or grouting the joints in brick masonry walls probably greatly exceeds the cost of the additional labor and supervision needed to make the walls water-resistant when built.

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