Basement waterproofing: how to patch wall cracks

Materials needed: hydraulic cement, pointed trowel, hammer, masonry chisel, wire brush, water.

If you are certain that water is leaking in at only one or two obvious places and the rest of the foundation is reasonably well waterproofed, it may be very possible to cure the leak with hydraulic cement. This cement can be used even as the leak occurs because it must be applied to a wet surface. The cement works by expanding as it sets, thereby filling and sealing the crack.

To prepare the surface for the cement, use a hammer and masonry chisel to enlarge the crack so that it forms a kind of dovetail shape, narrower at the surface and wider at the rear. The purpose of the dovetail shape is that the cement will have the firm support of the masonry to hold it in place.
Use a wire brush to remove any chips and loose pieces of masonry.

Following the directions on the cement package, mix only as much as you need immediately because it sets very quickly. The area to be patched should be soaked thoroughly with water before applying the cement. This prevents rapid hydration and improper setting. Then fill the crack and hold until it stiffens.

Hydraulic cement can also be used along the joint of the floor and wall. Make sure the surface is free of all dirt and dust. Chip away any loose mortar and make a dovetail-shaped opening along

the joint. A vacuum cleaner does a good job of removing dust particles. After wetting the area, mix only as much cement as you need. Use a pointed trowel to force the cement into the opening, and smooth the surface.

Check the basement after the next several rains. If the leak has been repaired, turn to the section on interior wall treatments to complete dampproofing the walls.