How to Seal Basement Walls to Keep Moisture Out

An empty basement with moisture stains on the wall and insulation in the ceiling.

When finishing or remodeling a basement, moisture can wreak havoc on any project. In fact, moisture buildup in the basement is a serious concern. Not only can moisture damage a home’s foundation, but it can also ruin personal items if the leak is not dealt with properly. Luckily, sealing basement walls to keep out unwanted moisture is an easy process. By following these simple steps, you can rest assured knowing that your basement is free of moisture.

Step 1 - Uncovering the Source

The first step in properly sealing a basement is to determine the source of the problem. Sometimes the leak is obvious to locate, especially if water is coming from cracks in the wall or floor. However, it is often difficult to tell the exact location of the moisture leak. If that is the case, then waterproofing the interior walls is the best way to ensure the moisture is properly handled.

Step 2 - Fill in Cracks

A man patching up damaged walls.

Whether or not you choose to waterproof all of the walls in the basement, filling cracks and gaps in the concrete is an important beginning step. Without these cracks properly filled, water can easily find its way back into the basement even after the walls are sealed. Fortunately, there are a variety of products available to fill in these holes, including cement or epoxy sealers. Simply follow the instructions on the sealer and make sure it is fully dried before applying sealant to the rest of the walls.

Step 3 - Concrete Sealers

Once all of the cracks have been sealed up, it's time to choose the proper type of sealer to waterproof the walls. If the walls have not been painted and the bare cement is exposed, there are two options to choose from: concrete and silicate based sealers. Concrete sealers act like an additional layer of concrete and dry in thick layers. Concrete sealer should be painted on with a heavy brush. Silicate based sealant, on the other hand, uses a chemical reaction to create a solid surface on the surface of the wall.

Step 4 - Acrylic Sealers

A paint roll painting white paint on a wall.

If the basement walls are painted, then waterproof paint is the best option as concrete and silicate based sealers cannot be used on painted surfaces. Acrylic paint acts very similar to regular interior paint, only it goes on thicker. In fact, one gallon of acrylic paint typically covers about one fourth that of ordinary paint. Thankfully, this type of waterproof paint can be painted on with a regular paint brush, spray brush or roll. Once it is dried another layer can be added for additional coverage.

Step 5 - Exterior Foundation

After the interior of the basement has been properly sealed, it's a good idea to check the exterior of the home to ensure the foundation is not prone to water contact. For starters, ensure that there is a slope going away from the foundation that drops at least two inches for every foot. You may need to add dirt to ensure the proper slope, but make sure that the ground is not making contact with any sill plates, which can cause rot down the road.

Step 6 - Gutters and Plants

A clogged gutter outside a house.

Another way water can easily enter the basement is through a damaged or disordered gutter system. In order to fix this, make sure that gutters are clear of debris to prevent water from improperly draining and spilling into the foundation. Next, ensure that all gutters are pointed away from the home and are located five feet or more from the foundation. If the gutters are all in order, check to see if any plants are less than a foot away from the house. Sometimes, plant roots can be avenues for water to reach the foundation.

Step 7 - Alternative Solutions

Depending on the situation, additional steps should be taken for more serious leaks in the basement. If waterproofing walls is not an option, then consider installing a sump pump. Sump pumps take out water after it reaches a certain level and pumps it away from the foundation of the house. An alternative to a sump pump is a French drain. These types of drains utilize a series of pipes that run below the basement floor and around the perimeter of the home. Lastly, if regulating moisture continues to be an issue even after sealing the walls, then consider adding a dehumidifier to help regulate the amount of moisture in the air.