How to Seal Basement Walls, Step-by-Step

By Amanda Lutz Updated February 1, 2024

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If you’ve noticed standing water on your basement floor, moisture along cracks in basement walls after a storm, or chronic musty odors, it’s time to think about waterproofing. Basements are vulnerable to groundwater intrusion because they sit below grade—especially those in old homes. But there are plenty of waterproofing solutions you can consider. We’ll guide you step-by-step through the process of finding the problem and determining the right solution.

 


 

When Should You Seal Basement Walls?

Here are some signs that you need to seal basement walls:

Addressing water intrusion is important for your foundation as well as your physical health, since mold is hazardous to breathe. On the plus side, waterproofing can be an opportunity to revitalize an underused space with an entire basement renovation. Before waterproofing, check your foundation walls, gutters, and downspouts to rule out simpler explanations for the issues above.

 


 

Types of Waterproof Coating

Basement walls are typically made with concrete, which is water-resistant but contains pores that let water in if not properly sealed. Waterproof coatings come in four common varieties, detailed below.

Plastic sheets and waterproof panels

Plastic sheets and panels work by trapping water between the wall and sheet and directing it downward to a drainage system and sump pump. This is a pricier solution than the other options in this guide.

Silicate concrete sealant

Silicate concrete sealants treat concrete by penetrating the material and closing gaps. Sealant cannot be applied over paint, so paint must be removed from your basement walls before application.

Waterproof concrete coatings

Waterproof concrete coatings also can’t be applied to painted walls. This sealant is for concrete and other masonry and must be applied with a special brush.

Waterproofing interior paint

Waterproofing interior paint is applied in a thick layer on top of other sealers for added waterproofing protection.

Hydraulic cement can also seal simple surface cracks, but it’s not effective as a long-term waterproofer on its own.

 


 

How to Waterproof Basement Walls

Waterproofing damp basement walls involves removing standing water, determining the water problem’s source, cleaning and prepping walls, sealing leaks, and applying waterproof coating. We’ll walk you through do-it-yourself (DIY) steps and explain when you should consider hiring a professional. You’ll need the following supplies:

1. Remove All Standing Water

First, make sure electricity to the basement is disabled, because standing water poses an electrocution risk. Then verify if sump pumps or floor drains are clogged or have failed. Finally, use a mop, wet vacuum and towels to remove standing water. Fans and dehumidifiers will help reduce humidity, and cleaning with a diluted bleach solution (with proper ventilation) can mitigate mold and mildew.

2. Find the Source of the Leak

An effective way  to find the leak’s source is to tape a 1-foot-by-1-foot square of aluminum foil directly to the basement wall. After 24 hours, observe the aluminum and note where any condensation is appearing.

Dampness on the side of the foil facing you means that your basement is humid and must be properly ventilated and dehumidified before waterproofing. Condensation on the side facing the wall means that moisture is entering from the exterior and must be addressed with waterproofing.

3. Clean and Prep the Area

Paint will need to be removed before sealing walls. Use a ventilator mask and gloves when you’re cleaning and prepping. First, scrub the walls with a dry brush to remove dirt and debris. Efflorescence, the white powder you often see on masonry, can be removed with muriatic acid solution. Allow the area to dry and apply acetone, scrubbing with the wire brush to remove paint. Rinse the wall and repeat this step as many times as needed to remove paint.

4. Seal Holes and Cracks

Holes and cracks can be sealed with products such as hydraulic cement, caulk, or epoxy resin. Companies like Drylok offer many waterproofing products for this application. Small cracks can be sealed with hydraulic cement, but larger cracks may indicate a deeper structural issue that should be handled by a professional.

Begin wall crack repair by inserting a caulking gun with your chosen sealer and plugging the gap until the resulting sealer is flush with the wall’s surface. Hydraulic cement can be spread over cracks, as it will harden into a protective layer, but work quickly because hydraulic cement can dry as fast as three minutes after mixing.

5. Reseal Doors, Windows, and Window Wells

Doors, windows, and window wells are common places water enters basements that can be sealed with caulk. Use a caulking gun to apply across joints and openings. Insert the tip of the caulking gun into the crack and then fill it with caulk, dragging sealer in a straight line across the area.

6. Apply Waterproof Coating

Silicate concrete sealant can be applied using a roller or spray-on application after cleaning dirt, oils, paint, and grease from basement walls. Lightly dampen the wall’s surface and apply two to three coats of sealant, waiting 10 to 20 minutes between coats for it to adhere. Wipe away excess sealant.

Waterproof concrete coating hardens into a rubber-like sealant and is a bit more flexible than other options. You’ll need a special mop to apply the coating.

You can also use waterproofing paint after other sealers to provide another layer of protection.

 


 

Professional vs. DIY Basement Waterproofing

You can waterproof your basement by following the steps above. You’ll need a ventilating mask and gloves for safety as well as patience, technical know-how, and the right equipment. We recommend hiring a professional to waterproof your basement if it has large cracks, frequent water intrusion, flooding, or water problems that are difficult to diagnose.

According to HomeAdvisor, the average homeowner spends around $5,000 on professional waterproofing. Wet basement walls, standing water, and moldy smells make your basement less comfortable. Preventing and mitigating these issues can make the space feel more homey now—and increase your property value in the future.

 


 

Insulation vs. Waterproof Sealing

Sealing walls with a waterproof coating will provide an interior barrier against water, but it won’t prevent water from getting in. Insulation, such as polyisocyanurate insulation boards, will prevent moisture from entering from the outside and increase energy efficiency. Other insulators, such as polystyrene foam, function similarly.

Basement insulation requires professional installation and costs $1.50 to $2.50 per square foot, according to Angi. Insulation is usually just one part of a multistep waterproofing process because while some insulators are waterproof, insulation is designed to minimize heat transfer and won’t provide the same level of waterproofing as a dedicated system.

 


 

Our Recommendation

Most homeowners can address small cracks and leaks in their basement on their own, but large cracks, significant standing water, and recurring issues are best left to professionals. We recommend trying to diagnose the water problem on your own to see if it’s within your technical abilities. If not, invest in hiring a professional.

 


 

How to Seal Basement Walls FAQ

What is the best sealant for basement walls?

Popular sealants for basement walls include Drylok, Foundation Armor, DAPConcrete, and RadonSeal. Properly clean and prep concrete basement walls before applying sealant.

How long does waterproof sealing work on basement walls?

Waterproof sealing works on basement walls for around 10 years with proper installation. Many companies offer longer warranties.

Should I waterproof my exterior basement walls?

Waterproofing exterior basement walls ensures they stay dry, but pricing varies depending on your foundation type and access to the area. According to HomeAdvisor, sealing crawl spaces can cost as little as $1,500, but exterior application of waterproof membranes can cost as much as $15,000. Homeowners spend an average of $5,000 to waterproof their basements. Solutions such as French drains cost $1,000–$10,000.