Things You'll Need
Wire or scrub brush
Masonry cleaner or muriatic acid
Bucket and grid or paint tray
Concrete and concrete block are common, but porous foundation materials. Older houses that haven't had drain tiles installed are especially prone to seeping walls and floors in basements. If the problem isn't severe, painting concrete in the basement with a moisture barrier paint can solve the problem. Most paint and hardware stores carry elastomeric, oil-based, or latex paints that seal almost all masonry against moisture. These moisture barrier paints are not guaranteed if the concrete is crumbling or badly cracked, but can be applied over repairs or under carpet and paneling to help keep your basement dry.
Scrub the concrete with a wire or stiff-bristle brush to remove loose material and efflorescence (a powdery white substance that often forms on damp masonry.) If there is a lot of efflorescence, scrub it away with muriatic acid or masonry cleaner--follow the label directions for proper mixing and use.
Repair cracks and holes with quick-drying concrete patch. Use the patch to fill in cracks where the wall meets the floor as well, even if you're not painting the floor.
Mix the paint well, both before and during application. Moisture barrier paint is very thick because it has a high solids content, and frequent stirring keeps the solids suspended.
Apply the first coat with a brush. You can also use a roller and brush, rolling small sections and then working the paint well into the surface with a brush while the paint is still wet. Let the paint dry according to label directions.
Paint the second coat using a brush, roller or airless paint sprayer. Apply the paint in a uniform, fairly thick coat.
Check the paint the next time conditions are right for leaking in the basement. If you see any leakage or seeping, wait until it's dry and spot-paint the areas where it leaked. All it takes is a pinhole of missed paint to allow moisture through.
Moisture barrier paint is available in both oil- and water-based formulas. It's OK if the masonry is slightly damp when you apply the first coat when using water-based product. Use a fan or dehumidifier to help it dry.
Most brands are available only in a limited range of colors, but can be painted over with regular interior or exterior paint after drying for at least 24 hours.
Moisture barrier paint may only cover as little as 75 to 100 square feet per gallon, per coat of paint. Compared with regular paint, you may use three or four times more to cover the same square footage.
Don't attempt to spray moisture barrier paint with a small paint sprayer. You'll need a large professional-quality sprayer and a spray tip with a large enough aperture to spray very thick material.