Bentonite as Backfill Compound

Sir,

Bentonite is a very expansive (changes volume, not "expensive" as in high cost) clay, often used as a water stopping material because of this property. Therefore, I would expect it to "soak up" water and swell a lot as the soil gets wet, then shrink and lead to cracking of the fill area during dry times.

If your location is subject to wetting and drying of the soils, I would think bentonite to be a poor choice. I have no practical experience in this use for it, so this is conjecture only. However, constructing anything in or over very expansive soil is much more difficult.

--JMM