Bentonite Waterproofing – Injection Methods & Cost

In this article, we’ll be telling you all you need to know about bentonite injection waterproofing, and why it is an ideal choice for protecting your basement against moisture.

One of the major reasons why your basement is vulnerable is the fact that it is surrounded by soil. This is because soil can absorb and retain moisture, which can penetrate through cracks in your foundation walls and into your basement.

To add to that, water damage can be a real problem for those who live in areas that are prone to flooding. This is why homeowners need to invest in basement waterproofing.

Luckily, there are several ways by which this can be done. One of which is bentonite waterproofing.

Sodium Bentonite

Bentonite waterproofing makes use of a form of clay known called bentonite. It takes a granular form and can be found in many parts of the United States.

In general, clay has the ability to absorb water and expand in the process. However, bentonite isn’t the same as other forms of clay, being that it has unusual and super absorptive abilities.

Sodium bentonite can absorb water until it has expanded to as much as 15 times its original size when dry. This makes it a very effective solution for two main reasons.

First of all, as water travels through the soil, a layer of well-positioned bentonite will absorb it before it can make contact with the walls of your foundation.

The more the bentonite expands, the better its protective abilities against water. This is because the expansion forces will cause the bentonite to handle more density.

And by the time the clay has gotten to its full capacity, it would have become very dense, that water would no longer be able to pass through at all.

What Is Bentonite Injection Waterproofing?

Bentonite injection and injection waterproofing as a whole has become a common practice over the years.

Bentonite injections specifically have been applied commercially for about 80 years and were a popular approach to maintaining cofferdams and sealing earthen dams for better water containment.

As for residential fixes, this method has been used for more than 50 years by contractors. Many contractors have even begun issuing warranties for your basement wall after repair with bentonite.

Generally speaking, bentonite injection waterproofing is when bentonite liquid mud is poured into a pressure gun and the content is injected into the cracks and gaps to seal the spaces and prevent water from penetrating.

How Does Bentonite Waterproofing Work?

As we have already mentioned, bentonite can be used to seal cracks and gaps in building foundations to protect the basement from moisture.

Bentonite has the ability to expand up to 15 times its normal size, hence absorbing more water and becoming denser until moisture can no longer pass through.

The more the bentonite clay expands, the more areas of the gaps it can cover. This ensures that the greatest possible amount of space is sealed in the process.

To get the best results from bentonite, it is recommended that it is applied during the construction phase of your home. This is not to say you won’t get good results if you apply it in the cracks of an already-existing home.

But it means you will have to first do some excavation before the new waterproofing clay is applied.

This would also mean you would incur some extra costs, and expend some time since excavation is a long process.

Bentonite can be applied in sheets, but can also be injected into cracks when it’s in liquid mud form.

Bentonite Waterproofing Process

Similar to almost all waterproofing processes, using bentonite requires some excavation around the foundation soil to be done before the process can begin.

Excavation takes time so you need to be patient while the work is ongoing. You will also have to bear with the inconveniences that come with the process.

For maximum protection to be guaranteed, you must expose the entire foundation wall so the bentonite can be applied all across without leaving any area untouched.

It is only by doing this that you can effectively execute one of the different methods of bentonite waterproofing.

The first method

The first method of bentonite waterproofing we shall discuss involves stacking loose bentonite into spaces between the soil and the foundation walls.

This method of bentonite waterproofing is pretty straightforward, although it has some downsides.

The first of which being the use of large amounts of bentonite to get the job done. This would increase the cost of completion, being that you have to buy a lot more of the material.

Another downside of this approach is that there is a risk of loose bentonite flowing into the soil, which means that your foundation will be less protected.

The Second Method

The second method of bentonite waterproofing aims at stopping excess bentonite from flowing into the soil. Using this approach, a layer of bentonite is set in between two geotextile sheets.

For those who don’t know, a geotextile is a form of tightly weaved and sturdy fabric, which is designed to allow water to pass through it while blocking off soil and other particles.

Further Considerations On Bentonite Injection System

As far as keeping water from passing through your foundation walls into the basement is concerned, bentonite gives you the same level of protection like other waterproofing approaches.

Nonetheless, we have to mention that bentonite cannot stop water from penetrating your basement through the floor or any crack that is located where the walls and the floors meet.

The good news is, most homeowners don’t have to fret about water entering their basement through the above-mentioned areas.

But if your home is located in an area that is low-lying or flood prone, then it would be in your best interest to employ a secondary form of waterproofing.

Combining the bentonite approach with one or two more waterproofing measures will surely guarantee that your basement stays dry at all times.

Installing a sump pump can do the trick. This machine is built to collect water and redirect it away from your basement. You can also install a French drain to support your bentonite waterproofing.

Disadvantages Of Bentonite Waterproofing

Bentonite clay is a great material to use for basement waterproofing, but it does come with its fair share of disadvantages.

Let us take a look at some of them below.

  1. A thick bentonite coating needs to be applied

This is one of the factors that cause homeowners to opt for other waterproofing options. A thin layer of bentonite will not stop water from getting into your basement, you will need a thick layer to achieve such results.

The more bentonite you buy, the more expensive the entire project becomes.

In a case where you fail to cover the entire area, groundwater will eventually make its way in.

  1. You need to carry out major excavation works

Most contractors will use bentonite sheets instead of the liquid mud injection to waterproof your basement.

However, a lot of excavation around the ground of your foundation has to be done before the sheets are applied.

This will not only take time, but it will also require the use of heavy machinery, which may change the face of your landscape in the process.

  1. Cracks remain vulnerable

Remember, bentonite won’t completely waterproof the cracks in the parts where the basement floor and walls meet. Also be reminded that soil hydrostatic pressure is usually on the high side after a heavy downpour of rain, which could cause water to enter your basement.

Frequently Asked Questions About Bentonite


Is bentonite a toxic material?

The good news is, bentonite is non-toxic, neither is it allergenic. Which means it will not irritate the eyes or skin when contact is made.

What amount of bentonite do I need to waterproof my basement

There is no universal answer to this question. The amount you will need depends on the size of the area you are planning to waterproof.

On the average, 7 to 10 pounds of bentonite per square foot should do.

Bentonite Waterproofing Cost

If you’re wondering how much it would cost to waterproof your basement using bentonite in 2021, then wonder no more.

Expect to spend about $85 per ton of bentonite. Now the soil characteristics and the size of the area being covered will determine the amount of bentonite you will need to buy.

Per square foot, you will need between 3 to 10 pounds of bentonite to complete the task.


Bentonite is great for waterproofing because of its ability to absorb water and swell to about 15 times its original size. The denser the clay gets, the harder it is for water to pass through it.

However, laying bentonite in sheets will mean you have to do some excavation around the foundation before the job can commence. This can be time consuming as well as inconvenient.

Make sure you consider other waterproofing options before you make your final decision on which approach is best for you.

Good luck!

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