Basement leaks not only make life miserable, but they can weaken the foundation of your home. Basement walls should seal out a moderate amount of water, but few will withstand a great deal of water pressure. If the wall leaks only during heavy rains, you may be able to solve the problem by adding extensions to your gutter downspouts to direct rainwater away from the basement walls. You may find that your yard slopes in a way that causes rain water to flow toward your home. If so, some corrective landscaping may be needed to solve your problem
For slow seepage: 1. Brush on interior sealer
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.
2. Fill any cracks
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.
For holes or cracks: 1. Widen and "key" the spot
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.
2. Mix the cement
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.
3. Apply the cement
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.
Sealing from outside: 1. Excavate to the trouble area
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.
2. Apply sealer
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 tar like bituminous sealer. Or, back plaster the wall with two coats of mortar (see Building Concrete Block Walls, Related Projects) and apply the sealer.
3. Install drainpipe and a barrier
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.
Also remember when you have the leaks repaired you need proper ventilation to prevent mold.