Bentonite is a clay type of soil that expands and contracts when it comes in contact with moisture. Bentonite may also be referred to as expansive soil.
But why are we, as realtors, making a blog post about soil? As realtors in Colorado we see this soil often due to Colorado soil containing lots and lots of clay. The issue with expansive soil is the negative impact it can have on your home and your home’s foundation.
Bentonite soil is a great option if you want to make your pottery stronger but the same can’t be said for the foundation of your home. When homes are built on top of bentonite if not properly engineered, the home’s foundation is at risk of cracking and shifting which can create severe structural issues. When a hard concrete foundation is built on top of a shifting soil it’s not too hard to see how this could cause severe structural damage. As the clay expands and contracts with Colorado’s wild weather the concrete on top of the soil will attempt to do the same. However concrete can’t shift… causing huge issues is the building’s structure.
Here are some tips we have when it comes to expansive soils:
1. If you are building a new home: make sure that you have a soil test completed on the lot where you want to build your new home. If the soil report indicates a high level of expansion (AKA bentonite) you will want the builder to use a foundation that can shift and cooperate with expansive soils.
2. If you are buying an existing home: this can be a bit more tricky, If the previous owner conducted a soil test; try to get ahold of the test and find out how much expansive soil you are actually dealing with. If a soil test is not available get the foundation inspected to see if there are any signs of the foundation shifting.
3. What to do if you find expansive soils: Make sure you don’t have any negative drainage that could create moisture around the foundation. Make sure there is no vegetation within 3 feet of the foundation. Make sure all downspouts have at least a 3ft extension. Ideally you should have 3ft of rock surrounding the foundation with positive water drainage.
4. What foundation works best for expansive soils: If you have the option or are willing to do the research on a home you’re looking to buy, look for a foundation built on caissons instead of footers. Caissons are water tight concrete cylinders that are drilled into the bedrock that stabilizes the foundation of the home.
