Dos and Don’ts of Waterproofing Basement Walls

Troubleshoot the causes and find the solutions to wet basement walls – the sooner, the better, to maintain the integrity of your home.

Top Tips for Waterproofing Basement Walls


Because they’re built below grade, basements tend to take on water. You may notice moist basement walls from time to time, water puddles here and there, or—worst case scenario—flooding during the rainy season. Humid, damp, or downright wet basements can result in peeling paint, mold and mildew growth, rotted wood, and damage to stored items.

While builders take steps to waterproof basements during construction, over time a house can settle, creating cracks in the basement walls. When the soil outside becomes saturated, water can seep through these cracks. Even structurally sound basement walls can absorb water from the soil and transfer it to the basement interior, making the walls feel wet. As the water from the walls evaporates, the air in the basement becomes more humid. A high-quality dehumidifier will help remove excess basement humidity, but the best long-term solution is to waterproof the walls.

RELATED: So, You Want to… Waterproof Your Basement

Depending on the reason for the moisture problem, the fix could be a simple do-it-yourself remedy, or it could require the assistance of a foundation contractor. If you’re looking at waterproofing basement walls, the following tips will get you started on the right foot.

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DO determine the source of the water.

Because concrete is porous, you can often see wet streaks that let you know where the water is coming in. Look for streaks along cracks, at the corners of windows, between mortar joints (for cement block walls), and around pipes where they enter or exit, such as a water-supply line or a sewer pipe.

If entire wall surfaces are wet, however, you’ll need to do further sleuthing. To conduct a simple condensation test, dry an area of the wall with a rag and then attach a one-foot square piece of aluminum foil to the wall with duct tape. Peel off the foil after 24 hours and check how the underside of the foil feels. If it is wet, water is seeping through the wall from the outside. If dry, the moisture is originating elsewhere in the basement, most likely from a basement shower—easily remedied by installing a vent fan in the bathroom to direct steam outdoors.

DON’T make wall repairs with standing water in the basement.

During a rainy season, a crack in a basement wall can allow an inch or two of water in, but before you seek to repair the crack, remove all the water from the floor. Working in a flooding basement increases the risk of electrical shock or electrocution. Turn off the power to the basement, and then use a utility pump (with extension cords that reaches an upstairs outlet) to get rid of the water. The pump will discharge the water to the surface of your yard via a garden hose. When the basement is water-free, proceed with inspecting, fixing, and effectively waterproofing the basement walls.