Basement Mildew

House Doctor | Gary Dymski

December 28, 2000

Q. I am interested in finishing my basement, approximately 750 square feet. My problem is a constant dampness and musty odor. I was advised to use bleach on the walls to remove the mildew and musty odor, then paint over it with an exterior latex paint with a mildewcide. The walls were painted by the previous owner, so I guess I cannot use a "drylock" paint unless I strip the walls. Do you have any suggestions on what I can use to treat the walls?

I have also heard that using a dehumidifier or air conditioner would help keep the basement dry. Any advice you can give me would be appreciated.

-Frank J. Buzzanca,

Holbrook

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A. You have several issues to consider, the first of which should be determining the cause of the musty odor and mildew in your basement. If you don't find the source of this dampness, no matter how well you clean and scrub, it will return. My guess is that because we live on an island with high humidity, you absolutely need a dehumidifier and a ventilation system in your finished basement. In fact, doesn't every Long Island homeowner use a dehumidifier in the basement?

Before you plug in your dehumidifier, by all means, clean the walls. Use a mild bleach solution, about a quarter-cup of bleach in a gallon of warm water. Scrub the walls with an old push broom and rinse them with cool water. You can wait till the spring or for warmer weather to do this, because you'll want to open your basement windows for ventilation.

Keep an eye on the walls for about a month. If the dehumidifier is removing enough moisture, the mildew and smell should not return. If it continues to smell, you might also want to add a ventilation system. Some companies specialize in circulating stagnant air to create a more comfortable living area. Start with a call to All Seasons Ventilation Inc. in Baldwin (516-223-0300). If you plan on creating a year-round living area in your basement, you'll want to have a source of fresh air.

Finally, you never want to paint an interior wall with and exterior paint. Without being too technical, there are solvents in paint that evaporate into the air. This process allows the paint to dry, but it also pollutes the air with something called volatile organic compounds (VOCs). Exterior paints usually have a much longer drying time than interior paints, and they often give off more toxic VOCs.

Clean the walls, use a dehumidifier and consider a ventilation system before you consider finishing your basement.