Sodium vs. Calcium Bentonite
There are two types of Bentonite clay. Sodium bentonite swells to 15 to 18 times its original size, whereas calcium bentonite swells only a little. If you put a tablespoon of each into separate glasses, fill each halfway with water and allow them to sit for a couple of hours, you would see the difference. The sodium bentonite would almost fill the glass, and the calcium bentonite would look pretty much the same. Because of its swelling properties, sodium bentonite is used in construction to seal foundations. Calcium bentonite is used for cosmetic and health care purposes. Sodium bentonite is strip-mined and is much cheaper than calcium bentonite.
Application of Sodium Bentonite to Seal Foundation Wall Leaks
When applied to a wall, Bentonite is mixed with water and applied with a trowel. If the leak is at the bottom of the wall, the Bentonite is troweled into the crack like cement, where it will expand and plug the hole. Cat litter can be used in this manner for small repairs, but remember that cat litter clumps, so you need to spread it quickly. For a large bottom crack, pour the dry cat litter onto the floor and sweep it into the crack or wash it in with a light spray of water.
Applying Bentonite to Areas with Standing Water
If you know where your foundation leak is, this method may work even when there is standing water. Sprinkle the bentonite into the water immediately over the hole. It will sink to the bottom and begin to gel, swell and fill the hole. It does not work immediately, and if there is too much incoming water pressure it may not work at all, as the clay simply will be washed away.
Considerations and Warnings
Bentonite clay expands quickly, but not immediately. It can take several hours to get the full effect.
Always wear a mask when using Bentonite clay powder, as inhaling the dust into your lungs can be deadly.
Sodium bentonite should never be taken internally. Clumping cat litter has been known to cause bowel obstructions and even death in cats that ingest the litter.