How much does bentonite waterproofing cost?

There are many methods that you can use to waterproof your basement. In this guide, we’re going to focus on bentonite and I’ll tell you everything you need to know about this  type of clay, how to use it and how much it costs.

How much does bentonite waterproofing cost?

The average bentonite price is typically $85 per ton. The average price for a bentonite sheet is $5 per square foot. How much bentonite you’ll use depends on soil characteristics. You can use anywhere from 3 pounds to 10 pounds per square foot.

Let’s take an example. Let’s say you want to waterproof your 1,000 square foot basement. Based on the soil characteristics in the area where you live, you need to use 6 pound of bentonite per square foot. This equals 3 tons of bentonite which translates into $255.

As you can see, bentonite is quite cheap. However, you can’t waterproof your basement using bentonite only. There are also many more steps to follow that imply using additional materials.

Now that you know what to expect in terms of costs when it comes to using bentonite for waterproofing purposes, let’s talk about more about this material and see what makes it so special.

What is bentonite waterproofing?

Bentonite is an absorbent clay of volcanic origin. It is used for waterproofing purposes due to its ability to expand in contact with water. When bentonite and water touch, the clay expands its volume and turns into a gelatinous mass.

As a matter of fact, bentonite can absorb 7 to 10 times its own weight in water. As a result, it can swell up to 15 times its dry volume.

Bentonite waterproofing cannot be used for all types of buildings.  There are pressure limitations beyond which the clay loses its waterproofing capacity. Ideally, bentonite should remain under a constant pressure of maximum 60 pounds per square foot.

⇒ Learn more: How much does waterproofing a crawl space cost?

How does bentonite waterproofing work?

Bentonite is used to seal building foundations from wet soil. In other words, the clay acts as a barrier preventing water damage. As bentonite expands in contact with water, it also fills the cracks in the foundation preventing water from getting in.

The best approach is to use bentonite waterproofing during the construction phase. Of course, you can also apply it with an existing building. However, you need to first excavate the foundation to do that. This method translates into additional costs and requires more time to complete.

Bentonite is usually applied in sheets. Another method to apply it is to inject liquid bentonite mud around the foundation. However, this second method is not very efficient.

Bentonite waterproofing disadvantages

As I stated at the beginning of this post, you can’t rely on bentonite only to waterproof your basement or the foundation of your house.

  • You need to apply a thick bentonite coating

If you apply a thin coat of bentonite, water will eventually enter you basement. While this may happen after just a few months or a few years, it will eventually happen. Bentonite is not a permanent basement waterproofing solution.

Not to mention that if you missed some spots, ground water will leak into your basement in a matter of days.

  • You need to carry out major excavation works

In most cases, you building contractor will use bentonite sheets. In order to apply the respective sheets, they need to completely excavate the ground around your foundation. This means using heavy machines which may damage your yard and even the foundation is the whole process is not carried out properly.

  • Cracks remain vulnerable

Keep in mind that bentonite cannot fully waterproof the cracks in the area where the basement floor and the basement walls meet. Soil hydrostatic pressure is very high after heavy rain and this may force water into your basement.

Frequently asked questions about bentonite

Is bentonite toxic? No, bentonite is not toxic to humans. This clay is non-irritating and does not cause any skin damage. As a matter of fact, bentonite is a commonly used ingredient in skin care products.

How much bentonite do I need in my pond? How much bentonite you use for sealing your pond depends on the surface on your pond. On average, you’ll need between 7 to 10 pounds of bentonite per square foot.


Bentonite is a cheap waterproofing solution. On average, a sheet of one square foot of bentonite costs only $5. You can use bentonite for basement waterproofing or pond sealing.

There you go, I hope this post answered all your bentonite-related questions. If you have any other questions and suggestions, feel free to use the comment section below.

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Last updated in October 2021 to add additional information.

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