If waterproofing is necessary, it should be applied to the outside face of the wall before backfilling. Different methods can be used, depending largely upon local conditions. By applying the coating to the outside, water is prevented from entering the wall. The water pressure tends to force the coating into tighter coritzct. If the coating is placed on the inside, water pressure through the wall may force it away from the wall surface.
Cement-Mortar Coatings
Where ground-water conditions are not a major consider lion and protection against dampness only is required, a coating of cement-mortar is usually applied over grout to the outside of masonry-unit walls. This coating consists of one, or preferably two, % -inch coats of cement mortar composed of 1 part of Portland cement to 2 or3 parts of sand by volume. The surface of the wall should first be cleaned and wetted until nearly saturated with water.
While still damp, but without water showing on the surface, it should be scrubbed with a grout coat of Portland cement and water of the consistency of thick cream. Before this coating has set and while still wet, the first % -inch trowel coat of cement mortar should be applied. Before this coat hardens, it should be scratched with a coarse broom or other tool to roughen the surface and provide a good bond for the second coat.
On the following day, the first or scratch coat should be dampened, and the second % -inch coat applied. The wall should be kept damp for 3 days or more.