Basement Waterproofing: How It Works & Costs

Tempted by ads that promise to waterproof your basement? Here’s the scoop.

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Image: Ruslan Sidorov/Getty

If you’re trying to figure out how to cure a wet or musty basement, you’re probably curious about advertisements for products that claim to waterproof basement walls. So you wonder, Is it really possible to dry out a basement simply by sealing the walls?

Yes, it is possible — but to make sure you’re choosing the right option, you need to figure out if the moisture is coming from the outside, or if high humidity is condensing on the cool walls of your basement.

How to Find Out What’s Causing the Moisture in Your Basement

Tape a 1-foot-square piece of aluminum foil to the inside of your basement walls and leave it in place for 24 hours. 

If there’s condensation on the outside of the foil, you have high humidity in your basement. Fix it with a portable room dehumidifier or a whole-house humidifier system instead of waterproofing products.

If the foil has condensation on the inside surface (next to the wall), the soil around your house may be naturally damp from a high water table or poor soil drainage. In that case, waterproofing your basement walls can be useful. 

You can waterproof just your interior walls, which may solve the problem. Or you can waterproof your exterior walls, which is a better bet — but more costly.

Here’s the scoop on the different types:

3 Types of Interior Waterproofing for Your Basement

Concrete Waterproofing Coatings

These thick coatings are cement-like. Once they 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 costs about $60.

Silicate-Based Concrete Sealers

Also known as densifiers, they are 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. One gallon costs about $65 and covers 175 to 250 square feet for one coat, but you’ll need at least two coats.

Waterproofing Paint Is an Acrylic Formula

It's 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 (one gallon costs $37).

Exterior Waterproofing for Your Basement: Costs & How It Works

The surest way to waterproof your basement walls is a full-scale exterior waterproofing solution. It can cost $10,000 to $15,000, depending on the work needed.

Exterior waterproofing involves excavating all around the house to the full depth of the foundation walls, then installing a waterproof coating or membrane topped by drainage panels. The panels provide an easy path for water to flow down to an exterior French drain at the bottom of your foundation. From there, water flows by gravity — or with the aid of a sump pump — away from your foundation to another part of your property or into a storm drain.

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Jeanne Huber

Jeanne Huber is the author of 10 books about home improvement. She writes a weekly column about home care for the Washington Post.