Waterproof coatings: our testing turned up one outstanding brand.(Keeping Your Basement Dry)(Cover Story)(Evaluation)

When your basement walls are damp to the touch or even seeping water, you may get temporary salvation with a waterproofing coating on the walls.

Despite their name, these products do not prevent water from entering through large cracks and holes; for that you need quick-setting hydraulic cement. And a wall that's always quite damp probably needs more than a coating.

Sold at home centers, hardware stores, and paint stores, these products can block the pores in the foundation walls that let water seep in. (They're properly termed coatings because they're thicker than regular paint, usually contain cementlike additives, and have to be worked into the wall with a stiff brush.)

We built the test rig shown on the facing page to measure how much water pressure each coating could withstand. The best worked reasonably well under the pressure from 8 feet of water. The worst could withstand pressure from only 2 feet of water.

THE BASIC CHOICES

Waterproofing coatings come in two forms. Here's how they differ and what we noted:

Premixed liquids. You stir them up and brush them on. Premixed coatings can be either water- or oil-based. The one oil-based product we tested didn't perform any better than its water-based counterpart; what's more, cleaning brushes and spills of an oil-based coating requires a solvent such as mineral spirits.