Concrete is a porous substance. Water and moisture can migrate up through the concrete, especially in areas where the concrete floor is placed below ground level. Heavy rains or improperly used drainage systems can allow groundwater to seep through the porous surface. Sealing or dampproofing concrete floors can be achieved as long as all cracks and breaks are filled in and moisture is removed from the area. This may include the permanent installation of a dehumidifier in areas such as basements or enclosed rooms.
Install a dehumidifier in the enclosed area that has a damp floor. Remove as much of the moisture as possible while you are performing the work to dampproof the concrete floor.
Seal all cracks in the floor and along the wall joints with a high-grade concrete sealant caulk. Ensure that the area to be caulked is as dry as possible. Most caulk products will not adhere to wet surfaces.
Place a foam sealant in all wall openings to cease the migration of outside air to the enclosed space, if applicable. Temperature variations from the outside environment to interior spaces will carry moisture along with the infiltrating air.
Apply an epoxy two-part sealer to the dry concrete floor. Follow the manufacturer's installation instructions. Various epoxy-based sealers will carry different instructions as to the installation process. Epoxy sealers will adhere better to the concrete surface than a clear chemical sealer or a latex-type sealer. Over time, the latex sealer may pull away from the concrete floor due to moisture migration. The epoxy sealer will permanently bond to the porous surface.
Install gutters to overhanging eaves that may allow water to flow under the grade level of concrete floors. Inspect the outdoor grade and landscape the ground so all water will flow away from the concrete floor and not back to the home.
Place a French drain system around the perimeter of the home. The gravel-enclosed perforated piping will carry away any standing groundwater and drain it from the area. In some cases the drain may have to be placed as deep as the basement floor level.
Treat only fully cured concrete floors. Concrete can take up to one year before any permanent sealer can be applied to the surface. Sealing a "green" slab may trap moisture under the sealant and cause premature cracks and breaks in the concrete surface.