How to Repair Leaks in a Basement Floor

  • 3-4 hours
  • Beginner
  • 10-50
What You'll Need
Stiff brush
Paint brush
Patching compound
Mixing container

Leaks in the basement floors are a common problem in homes. Whether the basement is finished or not, leaks in the floor can cause serious damage that can be costly if not repaired promptly. Not only can moisture from these leaks ruin carpets and wallboards, but it can also promote the growth of mold and fungus under the carpet and inside walls. This can lead to unsightly stains and unwanted health issues. Follow these steps to repair basement floor leaks.

Step 1 - Locate the Leak

repairing a crack in concrete

Before you can begin to repair the leak, you will need to locate the source. It will be less challenging to find it if your basement is unfinished.

A pool of water usually indicates the leak. Another indicator is a leaky foundation seam. If you have difficulty finding the leak, clean it up and watch the floor closely. You'll soon see the source of the water. If your basement is finished, you may need to pull up your carpet and pad or other floor covering in order to find the leak.

Typically, a leak in your basement floor comes from a crack in the floor or the seam where your concrete floor and foundation meet. However, ensure that it is not actually a result of water running down a wall or dripping from the ceiling.

Step 2 - Prepare Your Surfaces

Certain types of sealers and patching compounds cannot be applied over painted surfaces. Check the product label to determine whether the basement floor or the wall that adjoins your floor is painted. Then read the labels of sealers and patching materials to learn if they can be used on painted surfaces.

Step 3 - Repair Floor Cracks and Joints

crack in cement floor

To repair basement floor cracks that are larger than .25-inches, clean the debris and dirt from the cracks before applying the concrete patch. Remove all loose concrete debris using a brush or air hose. For cracks where water exists, until the leak has stopped before applying the patch. For leaky floor-wall joints, remove dirt and debris from the joint before adding the sealant.

Step 4 - Apply Waterproofing

After the patching compound is applied and settled, add the waterproof mix. If the crack or leaking wall-floor joint is still moist, use a water soluble formula. Otherwise, the waterproofing will not adhere to the edges of the crack or leaky joint. Refer to manufacturer’s instructions to determine the compound to water ratio.

Step 5 - Apply Sealant

Brush the sealant onto the wall with a stiff bristle brush that allows you to get the sealer into any cracks or pores. Spread the sealant only on the repaired concrete. Do not apply it apply more than two-inches from the leaking area. Allow the sealant to dry, then soak it with water. Let it harden overnight and add a second coat.