Understand your builder's bentonite soils test before buying

Obtaining the builder's bentonite soils test to determine the swell potential of the soil could save you tens of thousands of dollars later on by simply knowing what property you should or should not buy.

Pure bentonite (montmorillonite clay) can expand 15 times its normal size and exert a pressure of 40,000 pounds per square foot when it becomes wet. Expansive soils test showing 2% to 12% swell potential can result in various degrees of cracking and movement of your basement cement floor, garage floor, drive and walks, and in some cases, even foundation walls. The bentonite swell potential tests are typically available from your builder. You will want the specific swell potential numbers interpreted by a qualified person to determine if the swell potential is too great for your comfort level.

Be sure to also lean what you can do (or what a previous owner have neglected to do) to prevent swelling problems from occurring through proper landscaping, drainage and watering. One excellent publication from the Colorado Geological Survey Department of Natural Resources entitled Special Publication 43: A GUIDE TO SWELLING SOILS FOR COLORADO HOME BUYERS AND HOME OWNERS is available by calling (303) 866-2611 or you can order it Online for $7.00.

Further reading can be found at: EXPANSIVE DENVER SOILS - BENTONITE GUIDE: (Expansive Soils - Must Read Material)