A builder's most common complaint from homeowners is wet basements. The proper way to waterproof a foundation is to do it immediately upon removal of the forms. The most successful waterproofing method makes use of an unusual expanding clay material called bentonite. Bentonite is a rare, fine grained clay that has been used for many years to seal dams, ponds, reservoirs, canals, swimming pools and sewer lines. When water reaches the surface grains of bentonite, they swell up to 15 times their dry volume, automatically forming a barrier against water. This same material sandwiched between cardboard sheets makes easily handled panels that, when applied to the exterior surfaces of a basement wall, will keep moisture out permanently. When the cardboard in the one-fourth by 16 by 48 inch panels deteriorates, the bentonite remains trapped between the wall and the fill. It stays active indefinitely, drying out when the surrounding earth dries out. It springs into action when wetted again, stopping the water short of the foundation and any cracks that might have developed in it. The panels can be cemented onto the outside of the basement wall with mastic or they can be stapled or mailed on. Either method needs to hold only until the excavation is backfilled. From then on the pressure of the earth will keep them in place. The nailing method is preferable, since it is cleaner and faster. In many locations still further protection is needed in the form of inside drain tiling. This tiling system, which leads into a sump, prevents the seepage of water where the floor and wall meet. Many sumps are simply not deep enough to work properly. The hole for the sump should be dug 42 inches below the basement floor level. A 6 inch layer of No. 8 gravel should be spread in the bottom of the hole. Then a 36 inch high crock, 18 to 24 inches in diameter, should be installed. A stone backfill is placed all around the crock to give additional drainage for the underfloor water. The sump pump is installed low enough that the high water level is at least 2 inches below the tile where it enters the crock.