Types of Interior Waterproofing
1. Concrete waterproofing coatings: These thick coatings are cement-like; once dry, they adhere permanently to concrete and masonry walls. You apply the coating with a heavy brush made with tampico bristles — a natural fiber. Swirl the brush at the final stage of application to give the wall an attractive, finished look.
Concrete waterproof coatings can’t be applied to previously painted surfaces; check the label. A 5-gallon bucket (you add water to the dry mix) is $30-$40 and covers 100 sq. ft.
2. Silicate-based concrete sealers, also known as densifiers, are also suitable only for walls that haven’t been painted or sealed. The sealers soak in and chemically react with ingredients in the concrete or brick, forming a hard, waterproof surface.
Because these are penetrating sealers, they can’t flake off or peel, and you can paint over them (but check the label first). Applying a silicate-based sealer with a brush, roller, or sprayer is easy enough for a DIY project. A 1-gallon can is $40-$50 and covers 200 sq. ft., but you’ll need at least two coats.
3. Waterproofing paint is an acrylic formula, not all that different from ordinary wall paint. But you brush, roll, or spray it on much more thickly — one gallon covers just 75 square feet, not the 300 square feet typical with standard paint.
Waterproof paint is fine for DIY application. You can apply it over painted surfaces, and paint over it once it’s cured (1 gal./$35).
4. Plastic sheets and panels are suitable as wall waterproofing only in combination with interior basement drainage systems. They don’t stop water from getting through the wall, but they do stop it from ruining things in the basement.
Water that gets through the wall runs down the back of the plastic, into a drainage system in the floor. A sump pump moves water out of your basement. The entire system is $3,000-$5,000 for a 20-by-20-foot basement room.
TIP: None of these products will work unless cracks and gaps are properly sealed. So make sure you fill cracks and gaps less than 1/8-inch wide with polyurethane caulk made for masonry ($5/10-oz. tube). Patch wider cracks with epoxy filler