repairing a wet basement
Photo: Carolyn Bates

Also called sweating, condensation shows up as water droplets, wet spots, or puddles on basement floors and walls. It happens when moist, warm air hits cool foundation walls or uninsulated cold-water pipes, dampening carpets, rusting appliances, and turning the basement clammy. In crawl spaces, condensation encourages wood rot and insect attack, and can buckle and delaminate plywood.

Diagnosis. Condensation is easy to confuse with runoff or subsurface water. To tell it from the others, tape foil over damp spots and check it after a day. If moisture forms on the outer foil face, water is condensing from the air. If moisture forms on the foil underside, water is seeping in from outside.

Simple cures. Start with the easy stuff. If you have a full basement, air it out by opening windows and running fans. Also consider installing a dehumidifier (about $230 for a heavy-duty unit that will process 50 pints in 24 hours), ideally in a spot near easy drainage. Some experts argue that lowering the humidity in a basement will draw more moisture in, because moisture naturally migrates from higher humidity levels to lower ones. But as Chris Carter, of Ever-Dry in Fort Wayne, Indiana, explains, "The dehumidifier may draw in 10 to 20 percent more moisture, but it can easily process it." Bottom line: a drier basement.

During colder months, turn up the heat in the basement. Also insulate all cold-water pipes with foam insulation to keep moist air from contacting them, and be sure the clothes dryer vents to the outside with no duct leaks. Finally, don't dry clothes on a line in the basement or store wet firewood there.

Another effective solution is to damp-proof walls with a waterproof coating, such as UGL's DryLok Waterproofer (about $20 a gallon). Xypex's Hi-Dry ($21 for 5 lbs.) takes a slightly different approach. It's a crystalline penetrant that clogs concrete pores.

If your home has a crawl space rather than a full basement, cover the ground in the space with plastic sheeting 6-mil polyethylene is the most durable and generously overlap seams. You may also want to consider increasing the number of foundation vents to promote air circulation that will carry moisture away.

Severe cases. If you continue to see moisture after trying these cures, then you're not dealing with condensation.

Ask TOH users about Basements & Foundations

Contribute to This Story Below

    More in Basements & Foundations