It is critical to fix basement dampness problems before attempting to finish the space. Here are some of the most common causes of basement moisture problems. For each cause, you'll find a simple test or list of symptoms, information about the root causes, and some suggested solutions.Condensation
Symptoms/Tests: Damp walls, dripping pipes, rusty hardware, mildew. To identify condensation, tape a mirror in the dampest spot and wait 24 hours. If it's foggy or beaded with water, suspect condensation.
Causes: Excess humidity in the air, usually from an internal source, such as a basement shower, washing machine, or unvented dryer, or from a significant difference between the wall temperature and inside air temperature.
Solution: Install a dehumidifier, improve ventilation, and seal interior walls.Seepage
Symptoms/Tests: Dampness on a section of a wall or floor, most often on a wall near floor level. As with condensation, tape a mirror to the wall. If moisture condenses behind it, seepage is the culprit.
Causes: Surface water is forcing its way through pores in the foundation or an expansion joint. The source may be poor drainage or a leaky window well.
Solution: Improve exterior drainage. If problem is minor, an interior sealer may work. If not, waterproof the outside of the foundation.Leaks
Symptoms/Tests: Localized wetness that seems to be oozing or even trickling from a wall or floor. It usually appears during heavy rain. Test by running a hose outside near the leak. Pay particular attention to mortar joints between blocks.
Causes: Cracks that may result from normal settling or improperly poured concrete. (If you see a cracklike line running horizontally around your basement wall, it may be that the builders poured part of the wall and allowed it to harden before pouring the rest.) Faulty roof drainage or a grade that slopes toward the wall exacerbates the problem.
Solution: Improve exterior drainage. You may be able to plug several holes. For widespread leakage, waterproof the entire foundation and install drain tile.Subterranean Water
Problem: Subterranean Water
Symptoms/Tests: A thin, barely noticeable film of water on the basement floor is often the first sign. Test by laying down plastic sheeting for two days. Penetrating moisture will dampen the concrete underneath.
Problems: Usually a spring or a high water table forces water up from below under high pressure, turning your basement into a well. This may happen only during rainy periods.
Solution: Install a sump pump. Drainage tile around the perimeter of the foundation may help, but only if it drains to a low spot or a storm sewer.