Step-by-Step

Clean away dirt, grease, and dust from the wall. If you are using a cement-based sealing product, wet the wall thoroughly with a fine mist from a garden hose. Mix the liquid and powder components of the sealer thoroughly, and apply with a stiff brush.

As you brush, be sure to fill in all the pores in the wall. Go over cracks several times to fill them. If a crack is too large to fill in with sealer, use hydraulic cement (Steps 1-3). With some sealers, you must keep the sealant wet for several days to ensure bonding. Apply a second coat if necessary.

Enlarge the hole or crack with a cold chisel and hammer. Undercut it to make a "key" so that the plug won't come loose. Make the hole at least 1/2 inch deep. Whisk out fragments of concrete.

In a bucket, add water to the dry mix until it has a puttylike consistency. Then work it by hand. For a hole, roll it into the shape of a plug. Roll a long snake shape for a crack.

Squeeze the material into the opening. Keep pushing and pushing to make sure it fills every tiny crevice. If water is leaking through the wall at the time of the repair, it should stop running. Hold the material in place for several minutes to allow the patch to set.

If the problem is fairly high up on the foundation wall, you may be able to do the digging yourself. Otherwise, hire an excavating contractor to backhoe a trench wide enough for you to work in. Remove the dirt close to the wall by hand. Brush the wall clean.

You can hire contractors who specialize in this type of coating. To do it yourself, wash the wall clean, allow it to dry, and apply two coats of tarlike bituminous sealer. Or, backplaster the wall with two coats of mortar (see Building Concrete Block Walls, Related Projects) and apply the sealer.

Dig a trench along the footing and install a sloping, perforated drainpipe embedded in gravel (see Building Dry-Laid Retaining Walls, Related Projects). Stick heavy-gauge polyethylene sheeting to the wall sealer. Drape it over the footing, but not the gravel drain. Overlap all seams at least 6 inches.