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Is Bentonite Waterproofing Right For Your Home?

Sam Smith Foundation Repair Consultant

Bentonite clay is used as a protective layer over gaps in your basement walls

If you’re in search of accurate costs to install bentonite waterproofing systems on your foundation, you’ve come to the right place.

Here’s what you’ll learn by the end of this article:

  • What bentonite waterproofing is
  • How this waterstop solution works
  • The different types of bentonite and how they’re applied
  • Shortcomings of bentonite as a waterproof sealant
  • How to save money with bentonite waterproofing

Rainwater, runoff, groundwater, and the water in your soil all pose a threat to your foundation walls and concrete slab.

Hydrostatic conditions created by any water source or poor drainage can force water through your concrete and damage the inside of your home.

Many homeowners turn to bentonite as a part of their waterproofing system.

It’s a powder derived from volcanic ash that can be used in a few different ways to solve your wet basement problems.

In this article, we’re going to talk about what bentonite waterproofing is, how it works, and how you can use it to protect your crawl space or basement from water intrusion, even while on a budget.

What Is Bentonite Waterproofing?

Bentonite waterproofing comes in different forms that can be applied to your concrete block walls or basement floor.

They use bentonite, a very absorbent mineral powder, to create seals in any foundation cracks or damage.

How Does Bentonite Waterproofing Work?

Bentonite clay

Homeowners use bentonite clay as a high-performance waterproofing product because of its capacity to absorb and hold water. The clay is used as a protective layer over gaps in your basement walls and expands when it comes in contact with water.

The bentonite clay expands to fill the foundation cracks if it’s applied as a slurry. The seal created from the expanding clay is enough to stop water from penetrating the gap in the concrete.

The pressure in the substrate around your foundation can keep it from expanding outward if it’s put on the exterior basement wall.

The beauty of bentonite as a waterproofing method is that it will only expand when water hits it, making it a good solution for leaky basements.

What Are The Different Kinds of Bentonite?

Bentonite is sold in different forms and is applied differently depending on that form. I will review the six common kinds of bentonite waterproofing used on home foundations.

Sodium Bentonite

Sodium bentonite is the pure bentonite powder that is found in volcanic ash. It’s sold as a powder and isn’t suitable for vertical structures like basement walls.

Some contractors lay a layer of bentonite powder under concrete slabs to protect them from water damage and leaking.

It absorbs the most water of any type of bentonite and is the most effective at sealing. The powder sometimes makes application tricky, but it can be mixed into a mastic solution and applied like concrete.

Bentonite Waterproofing Sheets

Bentonite sheet waterproofing

Bentonite waterproofing sheets are more accessible and straightforward to use on your foundation.

They are sold in prefabricated, geotextile sheets made of polypropylene that can be installed on an underslab or the outside of your basement walls between the concrete and the soil. They usually are attached with a termination bar like any other flashing.

They offer more coverage than a bentonite clay and are usually very effective at combating water seepage. However, they’re tough to install around tiebacks and other abnormal concrete shapes.

Waterproofing Panels

Bentonite can also be installed using corrugated waterproofing panels. The channels get filled with bentonite and make for a waterproof barrier wherever they are placed.

They can be installed under slabs but are more effective when used on basement walls. Their rigidity makes them easier to install than sheets. They can also be used for blindside waterproofing in areas with a high water table.

High-Density Polyethylene (HDPE) Panels and Sheets

High-density polyethylene panels and sheets are made of nonwoven thermoplastic polymer that has bentonite heat bonded to it. The membranes hold the absorbent bentonite in place against concrete slabs or your foundation walls for protection.

Bentonite Waterproofing Membrane

Bentonite powder can also be mixed with a bonding agent that makes it bond to concrete. The result is a waterproofing membrane that can be sprayed like shotcrete or dampproofing or rolled onto your concrete walls or slab as a sealer.

Getting good coverage can be tricky but results in an excellent waterproof seal.

Trowel Grade Bentonite

Lastly, bentonite can be mixed into a cementitious solution that can bond with concrete like grout.

Trowel grade bentonite is straightforward to apply with a putty knife or trowel. It’s most often used as a crack filler for foundation walls to help limit water from seeping through small gaps.

What Is the Bentonite Application Process?

Bentonite usually gets applied to the outside of your concrete block walls or concrete slab because the hydrostatic pressure from the soil helps it create a good seal. The process of putting it on your concrete depends on which form of bentonite you choose to use.

Sodium bentonite can only be applied as a layer of powder under your concrete slab. Trowel grade bentonite gets put on with a trowel or putty knife, just like many other crack fillers.

Bentonite in panel or sheet form is laid or rolled out under your slab or on the outside of your basement walls before the area is backfilled.

Lastly, bentonite waterproofing membrane can be applied like any basement waterproofing paint using a brush, roller, or a paint sprayer.

Are There Problems With Bentonite Waterproofing?

Bentonite is a good solution for waterproofing your foundation walls and basement floor. However, it is far from perfect.

We will go over some of the shortcomings of this waterproofing material below.

Inadequate Coverage

Bentonite in any form needs to be applied properly and with good coverage. Leaving bare or thin spots in your application will leave your concrete open to water leaks and potential water damage.

Coverage issues are a good reason why some forms of bentonite should be applied by a professional who can offer a warranty on their work.


Leak on basement wall

Just like with any waterproofing product, bentonite does have the potential to leak. It can happen for various reasons, including improper backfill procedure, poor coverage, or because its absorbent quality is compromised by minerals or salt in your soil.


A costly aspect of any foundation waterproofing material that needs to go on the outside of your walls is the excavation. Of course, you need access to your foundation to apply bentonite to it.

You can expect to pay an average of $150 per linear foot for excavation and up to $200 if you have patios, driveways, or other blockages. This service can add over $25,000 to your application process.

Additionally, excavating and backfilling can potentially cause significant structural damage to your foundation or the waterproofing membrane if done improperly.

We recommend this cost be incurred for a safe and professional waterproofing process.

How Do You Save Money With Bentonite Waterproofing?

There are some ways you can bring down the price of your bentonite waterproofing project. You will see the most significant savings if you get your bentonite product of choice applied during construction.

You can save over $25,000 by installing alongside your foundation construction because you won’t pay for additional excavation.

You can also save yourself on the waterproofing process by turning the application into a DIY project. Again, we strongly recommend that you don’t carry out excavation or backfilling because of how damaging it can be if done incorrectly.

However, a handy homeowner can apply trowel grade bentonite to exterior foundation cracks after the excavation is done by a pro or to gaps on the inside of your basement walls.

Ultimately, we recommend you reach out to one of our seasoned professionals who can help identify any potential complications or additional worries with your unique situation.

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Sam Smith Foundation Repair Consultant
SHORT BIO: Hey, I'm Sam Smith. I'm one of our service techs here at Regional Foundation Repair. I'm here to help you learn more about your home's foundation. I've been doing this for a while, so I have a few insider tips and tricks to share!

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