When you occasionally discover damp spots in the basement, an interior cement-base sealer can help. Unfortunately, sealers work only on bare concrete, so if your block or poured wall has been previously painted, you'll have to have the basement wall sealed on the exterior of the house.
To apply concrete sealer inside on bare concrete, clean away dirt, grease, and dust from the walls using a stiff-bristle brush. Thoroughly wet the wall with a fine mist from a garden hose. Mix liquid and powder components of a cement-base sealer according to manufacturer's directions and apply with a stiff brush. As you brush, fill in all the pores in the wall. Go over cracks several times, if necessary, to fill them. If a crack is too large to fill with sealer, fill it first with hydraulic cement. Some sealers have to stay wet for several days to ensure bonding. Apply a second coat, if necessary.
Existing homes with extreme moisture problems may require exterior basement waterproofing—a costly proposition because dirt must be excavated from the foundation to allow sealers and/or membranes to be applied to the walls. If you're building a new home, be sure to have exterior waterproofing applied before the contractor backfills soil.
Continued on page 6: 6 Common Problems and Solutions