Bentonite is a type of clay formed from volcanic ash. It is an expansive soil, or swelling soil that contains montmorillonite minerals of clay. When water is mixed with this type of soil it expands, in pure montmorillonite can expand 15 times it s volume and soils containing montmorillonite may expand from 30 to 50 times it‘s original size. When it dries, then it loses volume. This expansion when wet can cause serious damage to any structure that is built on top of such soil. There can be cracks in the foundation, basements, floors and walls caused by a home being built on top of these types of soil. These types of soil also shrink when they dry out and this can cause problems with stability of the structure.
There are several factors that determine the amount that the soil expands. These include the type of minerals in the soil, the amount of moisture it is exposed to, soil density, and the amount of expansive clay that is present in the soil.
The best way to really know if your home has been built above these types of expansive soil is to have the soil professionally tested in a lab that specializes in this testing. The United States department of Agriculture produces a survey book on most of the counties and parishes in the United States. Recent editions of this book include information on soil and the composition of it. City or county offices for building inspection services and engineering dept. usually have a good knowledge of the soil composition of lots in their area.
If your home is built on soil that is potentially expansive then there are steps you can take to help protect your home from damage caused by water mixing with the soil and expanding it. The biggest thing is to avoid water getting near your foundation. Some steps that you can take are to not plant trees or vegetation that requires a lot of water within six feet of your home, fill in any spots around your home that are lower than other spots so that water can not pool and seep into the ground, clean gutters and drainage systems regularly, have any pavement, patios, etc slope away from your home so that water is not directed to pool near your foundation, do not set up sprinklers or irrigation systems so that water goes near the foundation, ensure that any metal, rock or plastic edging around gardens does not trap water in the area around your home and that driveways, walkways and paths do not lead water to the house rather than away from it. Ensure that everything around the house gives water the chance to drain away from the foundation.
When building a home on a site that has a strong presence of bentonite and other montmorillonite soils there are steps that can be taken in the design of the home to counteract and minimize potential damage such as using a geosynthetic clay liner, having a structural floor system that is suspended above the cement foundation and does not experience the damage caused by expanding and moving soil underneath the home.
It is important to know what type of soil your home has been built on and what steps you should take to ensure that your home is safe, stable and in the best shape possible.
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If you're ever in the market for Boulder real estate, be sure to visit Automated Homefinder & don't forget to ask your Realtor if Bentonite is a concern in the areas where you're looking. http://www.automatedhomefinder.com/co/boulder
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