What You Need to Know About Waterproofing a Basement with Bentonite

The wealth of different basement waterproofing strategies available today leaves many people confused about which method to choose. If you have a basement in need of waterproofing and would like to learn more about your various options, read on. This article will introduce you to the technique of waterproofing a basement with the substance known as sodium bentonite.

The Basic Idea

Sodium bentonite—often referred to simply as bentonite—is a naturally occurring and nontoxic type of granular clay. Like all clay, it possesses the property of expanding when it comes into contact with water. But in bentonite's case, this ability is greatly amplified. In fact, fully hydrated bentonite can swell to as much as 15 times its original size as a dry powder. Where waterproofing is concerned, this works to bentonite's advantage in two ways.

First of all, this means that when the exterior of a basement wall is sheathed in bentonite, any excess water present in the ground will be sucked right up by the absorbent clay. Second, once bentonite has swelled to its fully hydrated state, it becomes so dense that it presents an impenetrable barrier. In other words, saturated bentonite clay is just as effective at keeping water out of your basement as dry bentonite.

Bentonite on Basement Walls

In order to waterproof a basement with bentonite, the ground around the foundation walls must first be excavated to expose them fully. Once that has been done, there are a number of ways that bentonite may be installed. While simply filling the excavated area with loose sodium bentonite would prove effective for a time, the waterproofing would grow less effective as the bentonite migrated away from the house over time. Likewise, using this volume of loose bentonite would prove much more expensive.

Instead, bentonite is usually applied sandwiched between two layers of geotextile fabric. This durable fabric is porous enough that water can move into it, yet not so permissive as to allow the bentonite to escape. Bentonite can also be mixed with some sort of asphalt binder and then sprayed onto the walls of the basement. The asphalt helps to lock the bentonite firmly into place.

Potential Drawbacks

When correctly installed, bentonite offers a highly effective means of waterproofing a basement. That said, like all basement waterproofing methods, bentonite use comes with its own unique set of potential drawbacks. The principal drawback is the potential for human error during installation. If the exterior of the basement walls are not covered completely and evenly, you may find yourself dealing with leaks down the road. Finding a reliable installation contractor can greatly mitigate this worry.

The other main drawback of bentonite is that it is not capable of preventing water from seeping up either through the floor of your basement or through the crack where the floor meets the foundation wall. Thus, if you live in an area with an especially high water table, it may be a good idea to also install a stormwater system such as a French drain or a sump pump.

For more information, go to websites of contractors who work with stormwater systems.


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