A damp basement can wreak all kinds of havoc for a building if it results in mold growth, water damage or crumbling mortar. Most damp basements in need of interior waterproofing do not have the more serious concerns of water in the basement from a high water table or water gushing through cracks and holes. Interior basement waterproofing is a method best suited for basements that experience condensation on the interior walls or for small cracks and crevices in mortar or concrete. Serious water problems, such as a leaky basement from a high water table, require extensive exterior basement waterproofing with the removal of sub-grade soil and the application of a viscous asphalt and rubber waterproofing compound, but for minor water problems and cosmetic improvement, interior basement waterproofing can solve nuisances such as damp walls and efflorescence on the walls. Three common methods of interior basement waterproofing are the French drain, which involves extensive renovation; a baseboard system, which is less invasive but is best installed by professionals; and the application of waterproof paint, which is easy to apply but involves continual maintenance.
The French drain is a common waterproofing method for interior basement waterproofing. Invented not in France but in the United States by a farmer named Henry French in the late 19th century, the French drain directs condensate water from basement walls into a narrow trench cut into the perimeter of the basement floor. The trench is cut approximately 1 foot (30.5 cm) deep and is filled with perforated pipes that are covered with gravel. When moisture drips off the basement walls, the water collects into the pipes below the gravel. The pipes direct the water to a sump system at one corner of the basement, where the water is diverted to the exterior of the foundation or into a dry well or water basement drainage system.
The caveat to the French drain system, besides the cutting of the basement floor for its installation, is the potential for pipes to become filled with sediment over time. Pipes can be covered with landscape fabric that rebuffs large sedimentation and allows water to seep through. Maintenance is still required, though, to ensure that the system remains free of clogs and maintains a slight slope that diverts water toward the sump well.
The baseboard system is an effective waterproofing method that requires no invasive trenches cut along the foundation floor, but weep holes are drilled into the foundation walls or floor joints. Hollow vinyl baseboards glued to the basement flooring cover the weep holes and divert water to a sump well, where the water is pumped out of the basement. As with the French drain system, the baseboard system does not prevent water from entering the basement but diverts water that does seep into it.
Waterproofing paint is easily applied and maintained. Suitable only for concrete or concrete block foundations, concrete waterproofing paint is a viscous liquid basement sealer that bonds with the surface of the walls. It provides a superior impermeable water barrier for minor water problems such as condensation on walls and for interior mold control.