Bentonite

Sodium bentonite, a clay material, has enjoyed a steady upsurge in popularity over the past several years. In panel form, bentonite has become the choice of a growing number of architects and builders. Bentonite works because it can absorb a tremendous amount of water. As it takes in water, the clay swells to 15 times its original volume and pushes itself into cracks and voids. When it reaches its maximum volume, it stays in these areas permanently to seal against water. One firms panels are 4x4-foot corrugated cardboard with clay particles held within the flutes of the cardboard. The panels can be nailed, fastened with a powder-actuated tool, or simply laid in place for horizontal applications.

Some waterproofers are nervous about using bentonite panels. With other products, you can inspect the finished waterproofing application and confirm the integrity of the seal before backfilling. With bentonite panels, the seal doesn't form until the foundation is backfilled and water reaches the panel. Suppose something goes wrong? It's a nagging question for "traditional" waterproofers.

Bentonite has its advantages, however: It's safe to work with, non-polluting, easy and quick to apply, and can go on even at low temperatures. One company makes a sheet membrane that uses a compound of bentonite and butyl rubber.

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