Bentonite Waterproofing

Can a layer of clay prevent water from entering your basement?

Expensive and extensive. Installing a bentonite waterproofing system on an existing house usually calls for complete excavation of the foundation. Interior drain and sump pump systems are more affordable and also more effective.

Bentonite is a naturally occurring type of clay soil that has many uses. It is a primary ingredient in cat litter and in some pore-cleansing cosmetic products. Bentonite is also used by some contractors as a waterproof coating on basement foundations.

How does bentonite waterproofing work?

Bentonite waterproofing is an exterior waterproofing treatment that is supposed to work by forming a barrier between wet soil and the building foundation. Like any type of clay, bentonite absorbs moisture.

As water molecules bond to clay particles, the clay expands, filling cracks and gaps in the foundation so that water can’t get in.

Like any exterior waterproofing system, bentonite waterproofing is more effective and more affordable when applied during new construction. The clay is usually applied in thin sheets, but it can also be sprayed onto the foundation.

With an existing house, the foundation must be excavated in order to apply bentonite sheets. Alternatively, some contractors will inject liquid bentonite mud into the soil around the foundation.

What are the problems with bentonite waterproofing?

Before agreeing to have your foundation treated with bentonite, it’s important to know about certain
limitations and disadvantages. Here’s a quick rundown:

• Incomplete coverage. Like any exterior coating, bentonite can only provide effective protection against water intrusion if the application is perfectly done. Small gaps, missed spots and thin coverage are application errors that will allow ground water to enter the basement. This is especially true when bentonite is injected into the soil rather than applied in sheet form.
• Exterior excavation. For full coverage with bentonite, your foundation must be completely excavated. Bringing heavy equipment onto your property can be destructive to your yard and landscaping; it also turns your property into a major construction site. Care must be taken not to damage the foundation during the excavation process.
• Water leakage from inside the foundation. Bentonite applied to foundation walls can’t prevent water from entering your basement along the most common leak area: the crack between the basement slab floor and the basement wall. During wet weather, high hydrostatic pressure can easily force water up through cracks in the basement floor and along the floor-to-wall joint. Interior drain and sump pump systems are better able to provide waterproofing protection because they alleviate water pressure rather than causing it to increase.

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