How to prevent rain leaks penetration in walls

Masonry walls may be of solid brick or stone, brick packed with structural clay tile or concrete block, or concrete block painted or stuccoed. Walls of masonry that have been properly designed and well constructed have proved to be strong and durable, but when they are not well built, dampness may occur and cause disintegration of the walls if faulty conditions are not corrected. Dampness usually originates from one or more of four sources: leakage of drainage water from roofs and adjoining surfaces into the walls; penetration of wind-driven rain into the walls; condensation of moisture on the inside face or within exterior walls; or capillary rise of ground water from the soil.


Water that has penetrated the outside face of a wall may appear on the inside face far below the point of entry, making it difficult to locate the source of moisture. It is important, therefore, to check carefully ‘all points where leakage could occur. Poorly designed or defective flashings on roofs, parapet walls, and around chimneys should be replaced when necessary. Cracks in masonry units or in joints should be filled with mortar.

Rain Penetration

The possibility of rain entering exposed vertical surfaces of walls in amounts sufficient to cause dampness on interior surfaces depends upon the permeability of the wall, the wind velocity, and the intensity and duration of the rainfall.

Leaky joints that are otherwise in good structural condition may be made watertight by grouting. The grout can be made of equal parts of Portland cement and fine sand with enough water to give the consistency of thick cream. The joints should be dampened immediately before the grout is applied with a stiff fiber brush. Excess grout should be removed from the surface of the brick, but care should be taken not to disturb grout which has been deposited between the brick and mortar. This method of treating joints is not recommended for rough-textured brick.