Waterproofing a Basement Floor | Three Step Process

How to Waterproof a Basement Floor

Basement floor waterproofing is a three-step process. The first step is to fill and repair any existing cracks in your concrete slab. The second step is to apply a waterproof concrete sealer that protects your slab from rising moisture. The final step is applying an epoxy finish or similar product.

Last Updated: July 31, 2023, by: Rob Parsell

In this Home Flooring Pros How-To post, we will go into detail on the three step process of waterproofing a basement floor and show you the materials and tools you will need, as well as the associated costs.

How to waterproof a concrete basement floor

In our recent basement flooring ideas post we showed you some great ideas to inspire your basement remodel and the best flooring to go with it. Of course, all the ideas and options on show took one thing for granted…that your basement is completely dry with zero chance of future flooding.

If you are not in this fortunate position, then you will need to waterproof your basement floor and/or invest in a waterproof basement flooring product.

Those are two entirely different options, of course: Waterproofing vs Water Resistant Flooring.

This page tackles the first subject – How to Waterproof a Basement Floor.

Choosing the best waterproof basement flooring is covered in a separate post.

INTRODUCTION TO WET BASEMENTS

Do you have a wet basement? Is water puddling in your basement? If so, repairing the source of a significant amount of water is key to a healthy, mold-free environment. Here are some of the steps you wil need to take:

  • Check, repair and replace leaking pipes.
  • Consider exterior waterproofing to cover cracks in the foundation walls.
  • If excavation is needed to expose the foundation walls, that is a good time to add drain tiles, perforated pipe or a French drain around the footings of the foundation. Different methods are used regionally to combat water seepage into the basement.
  • Check, repair and replace gutters around your home – leaks from gutters allow water to fall next to the foundation, and it will find its way into cracks in the masonry.
  • Install an interior drain for minor issues and sump crock and sump pump to combat a wet basement – or make sure the pump you have is in good condition.

These big projects are beyond our scope here, but if you have major foundation water issues, they should be addressed before waterproofing the interior concrete slab. This is important work so know your rights when employing waterproofing contrcators.

And if your basement has high humidity, consider a dehumidifier to produce healthier indoor air quality and reduce the chance for mold and mildew to grow and musty odors to fill the air. This is especially important if you are planning a finished basement.

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OK, on to waterproofing your basement floor.

STEP ONE – FILL BASEMENT FLOOR CRACKS

Moisture gets to the surface of your basement slab in two ways: Water seepage through cracks in and around the perimeter of the slab where it meets basement walls, and moisture migrating through the concrete.

Migrating moisture? Yes. Water works its way up through concrete due to hydrostatic pressure in the soil beneath and around your home’s foundation.

Efflorescence is a sure sign that this is happening – a filmy whitish-gray residue on the concrete’s surface. Water brings minerals with it. The moisture evaporates, and the minerals are left.

Job 1 is to fill the cracks with a high-quality concrete crack filler. It will prevent water from surging up through them – and help keep any radon in the soil beneath from entering your living space. The filler also prevents the sealer or epoxy you cover the floor with from seeping into the crack and disappearing, rendering it ineffective.

Plus, if the cracks aren’t filled, they will likely telegraph through the flooring.

OK, hopefully you’re convinced to fix the cracks, not just cover them.

HOW TO FILL BASEMENT FLOOR CRACKS

We have a whole post dedicated to repairing cracks in a basement floor but here is a summary of what you will need and how to do it.

You will need:

An angle grinder – optional but recommended ($45+)

Metal 1” putty knife or wire brush ($3 – $15)

Shop vacuum ($55 – $200)

Crack filler – Liquid for small cracks ($15 – $50), caulk for medium cracks ($15 – $50+) or flexible rope for large cracks ($75-$150)

It’s a short and affordable list. If you don’t have the power tools, they are a good investment that you will use often as a DIY homeowner.

Step by step crack filling in the basement:

1 – Use the angle grinder along the entire length of the crack, like this. The purpose of this is to get debris out of the crack and to give the filler a clear seat.

2 – Vacuum the dust, dirt and debris out of the crack. If bits of concrete stick in the crack, use a metal putty knife or a wire brush to remove it. This allows the filler to fully fill the crack without impediment.

3 – Use liquid crack filler if the crack is less than 1/8” wide. Choose caulk for cracks up to 1/4” and a lot of caulk or rope crack filler for cracks up to 1/2″.

*If the cracks in your basement floor are wider than that and/or if the slab is sunken, your best next move is to get estimates from concrete professionals for recommendations and estimates on major foundation repair.

4 – Use the putty knife to smooth the crack filler and make it level with the basement floor.

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STEP TWO – APPLY WATERPROOF CONCRETE SEALER

One of your goals in this important home flooring project is to waterproof the basement floor against the transfer of moisture from below.

Whether you cover the slab with epoxy or flooring, using concrete sealant to protect your basement against the migration of moisture is a quick, cheap way to get the job done.

Anti-radon Bonus! Did you know that some basement concrete floor sealers are formulated to resist the transfer of radon through the concrete into your home? Protect your basement and your household with one vital step.

What it is: Most concrete sealant is acrylic liquids that flow easily to make installation a breeze. Your local home improvement store will have a range of products such as EnduraSeal Semi Gloss sealer and Foundation Armor Basement Wall & Floor sealer. Each has a wet look when dry, and these products resist yellowing with age.

How it is installed: Sealers are applied with a large paint roller.

For the best adhesion and performance of the paint, it is recommended that you clean the concrete first. Using an acid etch to open the surface of the concrete to improve absorption of the paint helps too. Products like Seal-Krete Clean N Etch handle both of these functions. Most cleaners are applied and then scrubbed into the surface to maximize their performance.

How much it costs on average: The most affordable way to buy a waterproof basement floor sealer is in a 5-gallon bucket. The average cost is $20-$30 per gallon, and each gallon will cover 150-200 square feet depending on how absorbent your concrete is. That comes to just $0.10-$0.20 per square foot.

Concrete cleaning products like Seal-Krete Clean N Etch cost $20-$30 per gallon with similar coverage to epoxy paint.

WHAT IS NEXT?

If you plan to install moisture and water-resistant carpet, floor tiles or other flooring materials suitable for below grade, then your job is done for now.

However, you might want to consider a waterproof, long-lasting alternative to traditional basement flooring – and that option is epoxy or a similar coating.

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STEP 3 – APPLY EPOXY OR SIMILAR COATING

As a waterproof flooring for basements there’s no easier solution than applying a coat of durable epoxy paint to your concrete slab. Epoxy basement floor cost is fairly cheap making epoxy an affordable waterproof flooring option. It does not require a vapor barrier – it is applied directly to clean concrete.

What it is: Epoxy is a polymer resin with waterproofing characteristics. Epoxy paints are formulated with tint to provide color. The most basic and affordable epoxy basement floor paints are gray. Among the more popular epoxy paints are Anvil Eclipse and Rust-Oleum Epoxy Shield.

If you want to take waterproofing a basement floor to the next level, consider an epoxy coating. These products require a two-step application that includes a hardener. The materials are typically referred to as Part A (the epoxy resin) and Part B (the hardener). With epoxy coatings, you’ve got many more appearance options including 30+ colors for most products or the blending of metallic flakes and other materials to enhance the look. Leading brands of two-step epoxy basement flooring are Epoxy-Coat, Rust-Oleum, Valspar and Epoxy Master.

How it is installed: Epoxy paint is typically applied with a paint roller. Shaking or stirring is usually needed. Pour it out into a paint pan, fill your roller with a medium amount, and roll it on generously. In short, follow the manufacturer’s label guidelines. Be sure to check what is called the “pot life,” which is how long you have to apply it before it sets up too much to be rolled.

How much it costs on average: Epoxy paints range from $25 to $45 per gallon, and most products cover 200-300 square feet per gallon depending on the viscosity of the product and how porous your concrete floor is.

If you move up to an epoxy coating, expect to pay $275-$325 for a kit that will cover 500 square feet. In other words, epoxy coating cost is about $0.60 per square foot. Most kits contain tint and/or flakes, but both tints and flakes are available for sale independently too. Flooring contractors install epoxy waterproof flooring too at a cost of $5.50-$10.25 per square foot.

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About the Author:

Rob Parsell

Rob joined the Home Flooring Pros team in 2014 and is a freelance writer, specializing in flooring, remodeling and HVAC systems (read more).

“I’m the son of an interior designer and picked up an eye for design as a result. I started hanging wallpaper and painting at 14 and learned enough on the job to be the general contractor on two homes we built for our family and did much of the finish plumbing, electrical, painting, and trim work myself.”

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