Repair Basement Leaks

If you have puddles or pools of water from a leak, remove anything that may become damaged and clean up the water with a mop or towels. Remove any mold or mildew that might have formed (see project Remove Mold from Walls).

Next, remove any loose or broken mortar, dirt, dust or other debris around the leak, using a broom or stiff brush. Clean the surface thoroughly. Waterproofing works best when applied to a clean, bare masonry surface.

To remove old paint, use a wire brush or sandblast the surface. Use muriatic acid to get rid of efflorescence — white, crystal-like salt deposits that form on the wall from moisture. Any efflorescence left on the wall will prevent a sealant from sticking to the wall. Any holes should be patched with hydraulic cement.

Safety Alert!

Muriatic acid is highly corrosive and can be harmful to your skin. Wear protective clothing, safety goggles and protective gloves when working with muriatic acid. The fumes from muriatic acid can also be harmful. Be sure you're working in an area with proper ventilation. In a basement, you may need an exhaust fan to help ventilate the area. Muriatic acid can also damage other surfaces. Take care when applying the muriatic acid to walls.

Now that you've prepped the surface, you're ready to apply sealant to your basement walls. For the best results, apply the first coat with a nylon or polyester bristle brush. The second coat can be applied with a brush or masonry roller. Work sealant thoroughly into the pores of the masonry surface. After using the first gallon, measure the area covered. It should be about 75 to 100 square feet. If the area is more than this, you're spreading the sealant too thin.

Apply a second coat over the entire wall surface. If seepage is still present after several days, tiny pores or pinholes are still open, then apply an additional coat to these areas.

Helpful Tip

Sealant won't adhere to a wall with a temperature less than 50ºF. Also, most wall sealants aren't made to withstand foot traffic, so don't use them to waterproof your basement floors.

Water that leaks through your basement floor usually gets there at the floor/wall joint or via cracks from the foundation/floor settling over time. Apply hydraulic cement to this joint to seal it.

To fix a floor crack, open it up using a chisel and hammer. Make the inside of the crack larger than the outside by chiseling at an angle. This will allow for a better seal. Clean out the concrete pieces and dust in the crack with a stiff brush.

Safety Alert!

Wear safety goggles when using the chisel and hammer. Concrete and cement can chip and potentially project small particles into your eyes.

Following package instructions, mix hydraulic cement with water in a bucket. Use a trowel to mix it and combine the two until the mix is homogenous. Dampen the crack by misting it with water from a spray bottle then pour the hydraulic cement mixture into the crack. You should pour to within ¾" from the floor surface. Let this dry for an hour or two then add another layer of cement mixture over the crack. Use your trowel to make the cement patch level and smooth with the floor surface.

Congratulations! You've rid your basement of leaks and it should remain dry for years to come.