Angie's How To Waterproof Your Basement

Date Published: Nov. 12, 2019

Time: 60 Minutes

A damp basement presents three major problems: it smells funky, it's not safe to store your possessions down there and it can lead to mold. Basement moisture can be caused by different issues – some are easy to fix and others require more effort. If you have a consistently damp basement, follow these steps to discover the source of the problem and then consider your waterproofing options.

Get quotes from up to
3 pros!
Enter a zip below and get matched to top-rated pros near you.
Zip Code

One of the most common sources of basement moisture is a drainage problem around your foundation. To check this, inspect your foundation during, or immediately after, a heavy rain. Look for any place where water is pooling near your house, particularly around the downspouts. If your downspouts are dumping water less than five feet away from your house, that may be your problem. To fix this, purchase gutter extensions at your local hardware store, which cost $10-$50 depending on their length.


Note: If this doesn't solve your drainage problem, or water is pooling in areas other than your downspouts, it's best to contact a professional landscaper – you may have a grading issue, which they'll be able to fix.


If you don't have water pooling outside, it's time to find out whether the moisture is coming from the air in your basement or from the soil behind your walls. This is easy to do! Tape a 1'x1' piece of tin foil to your wall and leave it there for 24 hours. If condensation builds up on the outside of the foil, you probably have high humidity in your basement. To fix this, consider purchasing a dehumidifier ($150-$250) to reduce moisture and prevent mold. If condensation builds up on the inside of the foil (the side facing the wall), moisture is probably coming from the soil behind your walls, and taking further waterproofing action will be useful.


Before you can add a waterproofing layer to your walls, you need to seal any cracks or gaps that are larger than 1/8-inch wide. It's best to use a polyurethane caulk that is designed for masonry, which will cost $5-$10 a tube.


There are two basic types of waterproofing materials that can be applied over walls and floors. Waterproof coatings (like Super Thoroseal) have a consistency similar to concrete and can generally only be applied to unpainted walls and floors. Coatings generally cost $30-$40 for a 5-gallon bucket, and are a good option if you can identify specific areas of your wall that are leaking. Waterproofing paints (like DryLok) are far easier to apply over a large area. Waterproof paint generally costs $15-$20 for a quart, and are a good option if your walls only get a little damp, but you can't pinpoint exactly where the moisture is coming from. Whichever type of waterproof material you choose, make sure you carefully follow the instructions on the can!

Related Pro: Local basement waterproofing contractors