Does Flex Seal Work on Basement Walls?

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You’ve probably seen people on various online forums discussing DIY hacks on fixing leaks and breaks. And you may also have seen most of them mentioning and recommending effective products, including Flex Seal. However, if you’ve never used it, you may wonder whether Flex Seal works on basement walls.

Flex Seal works perfectly for waterproofing basement walls. In fact, it is one of the best products to consider when repairing leaks or preventing potential ones. It adheres to different surfaces, including concrete, porcelain, cement, vinyl, rubber, and aluminum.

Finding a good sealant for your porous basement walls is crucial since water leakage can cause structural damage. In this article, I’ll discuss the effectiveness of Flex Seal in waterproofing basement walls. Now, let’s get started!

Flex Seal: What It Is and How It Works

Flex Seal is a thick, rubberized liquid that seals and coats openings on numerous surfaces. Therefore, it’s a great product when you want to repair notorious or even hairline cracks on your basement walls. Moreover, Flex Seal is non-toxic.  

Flex Seal is a perfect solution for any leakage in your home. Apart from sealing cracks, the sealant prevents corrosion and rust. You can also apply it on many surfaces such as: 

  • Tiles
  • Concrete
  • Wood
  • Drywall
  • Porcelain
  • Aluminum
  • Plastic
  • Vinyl
  • Cement

Flex Seal is available in different forms, including:

  • Flex Seal Liquid (black and white) – This is a thick rubberized liquid that forms a strong, flexible, waterproof coating on any surface. You can apply it using a roller or brush or pour it on the affected area.
  • Flex Seal Shot – This one is a thick rubberized adhesive sealant. It bonds, seals, and caulks several surfaces to form a watertight barrier. You only have to push the nozzle and apply it to the surface.
  • Flex Spray – Flex Spray is a rubberized sealant packaged in an aerosol can. It is ideal for quick fixes since you don’t have to use a roller or brush to apply it. The spray has great adhesion to both wet and dry surfaces, sealing cracks and preventing leaks.
  • Flex Tape – Flex Tape is a sturdy waterproof tape that adheres to numerous materials. Therefore, it is an effective sealant that you can use to patch or seal different surfaces.

Flex Seal is weather-resistant, so you don’t have to worry about using different sealants every season. Hence, it doesn’t drip and sag in summer or crack and peel during winter. Additionally, the sealant dries quickly, and your wall will be good to go 24 hours after applying it.

Is Flex Seal Suitable for Waterproofing Basement Walls?

Flex Seal is suitable for waterproofing basement walls. The sealant fixes holes or cracks on the walls (and other surfaces) to prevent water seeping through. Moreover, it is easy to apply and adheres to the surface for months.

If you’re worried about leaking basement walls, Flex Seal is one of those products you can rely on. Many customers on online stores, including Amazon, have acknowledged their satisfaction with the sealant, with 72% of over 3,000 reviewers giving it a 5-star rating. Although some of them had reservations about the product, most said that it works great on basement walls.

Flex Seal is suitable for both interior and exterior surfaces. So, you can waterproof your basement walls from the inside. However, since it has a strong odor, it’s crucial to ensure that your basement is well ventilated.

How Do You Flex Seal Your Basement Walls?

Flex sealing your basement walls is a straightforward procedure that involves cleaning the area and applying the sealant. However, you first need to establish the root cause of the leakage before you proceed. The application will also depend on what form of Flex Seal you’ll be using.

Here’s how to flex seal your basement walls using Flex Seal Liquid and Flex Shot:

1. Identify the Cause of Leakage

If you’re repairing your basement walls due to water leakage, it is vital to establish the root cause of the problem. The issue may either result from a primary or a secondary factor. A primary leakage cause could be cracks or holes in the basement walls.

On the other hand, secondary causes could include the following:

  • Poor water drainage
  • Cracks in the foundation wall
  • A close water table
  • Indoor humidity
  • Hydrostatic pressure from flooded water
  • Condensation from cold pipes
  • Melting snow or rainwater

2. Gather your Materials

Although applying Flex Seal on your basement walls isn’t a difficult process, you need a handful of materials to get the work done. Therefore, after identifying what is causing leaks on your basement walls, it is advisable to assemble everything you need before starting the procedure. You’ll require the following:

  • Wire, utility, and paint brushes
  • Fan (or dehumidifier)
  • Shop vacuum
  • Efflorescence remover
  • Plastic sheeting or drop cloth
  • Paint roller
  • Paint tray
  • Flex Seal Liquid 
  • Flex Shot

3. Prep the Basement Walls

You should ensure that your basement walls are clean before flex sealing them. Therefore, clean them using a wire brush. Moreover, wear protective gear, such as facemasks and disposable gloves to protect yourself from harmful odors or objects.

Due to moisture build-up, your basement walls could also have some crystalline salt deposits (efflorescence). If you notice any, use an efflorescence remover to get rid of the deposits. You’ll need a utility brush to apply the diluted solution and then rinse it off using clean water.

Also, get rid of paint dust, dirt, or concrete using a shop vacuum. Then, use a fan or dehumidifier to speed up the drying process as Flex Seal adheres better on dry surfaces.

4. Apply Flex Shot

Once your basement walls are dry, you can proceed to the application procedure, where you start by applying Flex Shot. However, go through the given instructions keenly to understand how to apply it. Moreover, also ensure that your basement is properly ventilated to prevent suffocation.

To apply Flex Shot, press the nozzle on the affected area directly. You can also push it into the cracks using your finger while wearing a disposable glove. This will allow the sealant to adhere better. Once you’ve applied it to all the cracks or holes, let the sealant dry for 24 hours.

5. Apply Flex Seal Liquid

After Flex Shot has dried, you can now apply Flex Seal Liquid. The liquid sealant is ideal for larger areas. Like Flex Shot, the liquid seals cracks and protects surfaces from leaking.

To apply Flex Seal Liquid:

  • Tape the walls using blue painter’s tape.
  • Spread the plastic sheeting or drop cloth on the floor to prevent any spillage.
  • Open your Flex Seal container and stir it gently.
  • Using a paintbrush, apply the liquid sealant on the walls, starting from the edges.
  • Once you’ve painted the edges, use a roller to spread the sealant on the whole wall.

Apply more than two coats of Flex Seal Liquid and let it dry for 24-48 hours.


Flex Seal is an ideal sealant for waterproofing your basement walls. The thick rubberized liquid seals all gaps and cracks to keep your walls leak-free. You can also use it on other surfaces, depending on your needs.

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