Bentonite is a kind of clay that has the unusual features of cohesion, bonding, stamping and thickening. It is usually gray (even white) and when processed, there is the durability of fine dust, similar to cement or dust. When bentonite is placed under the surface as a waterproofing membrane, it moisturizes with the moisture present naturally on the ground and forms an impermeable barrier that absorbs and discharges water and most chemicals such as acids and salts (sodium bentonite). Bentonite can be expanded and contracted many times and is capable of absorbing seven to 10 times its water weight, inflating up to 18 times its dry volume. However, for bentonite to function properly as a waterproofing barrier, it is extremely important that this barrier remains under constant pressure per square meter.