ABSTRACT
Bentonite is a traditional waterproofing material whose use goes back almost a century. Contemporary bentonite products evolved from the basic material first used for waterproofing in the mid-1920s. Used only in granular form in those days, bentonite use was limited to sealing pond liners and compacted-earth dams until the late 1950s when it was introduced to the building waterproofing market. The replacement of traditional forms of bentonite follows the pattern set by metallic oxides' replacement by crystalline coatings and built-up membranes' replacement by self-adhering modified-bitumen sheets. Sprayed and trowel-grade membrane bentonite products have virtually disappeared from the market, a consequence of the difficulty in applying uniform thickness and a tendency to pre-hydrate. Bentonite membranes that incorporate a geomembrane have lower moisture vapor permeance than membranes without the polymeric liner. Bentonite is comprised primarily of sodium montmorillonite, an inert mineral made of microscopic clay platelets with a laminated crystalline structure.
