Q. We never had a problem in the basement of our 1930's house (no water to speak of) until a few years ago when we began to notice a strong musty smell, despite having a dehumidifier (albeit a very old one) running and the upstairs door to the basement closed. The basement is unfinished, with cement-block walls and a poured concrete floor. It's a partial basement (under the central part of the house) with crawl space under other parts. It has a drain in the floor, and a door to the outside, but no windows. Would it be enough to scrub the basement floor and walls with TSP, and paint with a mildew-preventing paint, or another kind of paint? Who might we hire to do such a job? S.S. Ann Arbor.A. The terms "crawl space" and "musty smell" are often found together in sentences. It's not serendipity. The fact is that many crawl spaces are damp, and that dampness often leads to mildew and mold formation--and musty smells. In your case, it's likely that the crawl spaces are contributing to the dampness in the main part of the basement; dampness that the dehumidifier is working to remove. So, before embarking on cleaning or painting projects, it would be a good idea to minimize moisture infiltration into both the crawl spaces and basement. Many crawl spaces in homes the age of yours do not have a concrete floor. Bare dirt allows moisture in the earth to rise into the air as water vapor. However, even if the crawl spaces do have concrete floors, it's certain that they don't have a vapor retarder under the concrete (in new construction this consists of plastic sheeting laid on the ground before the concrete slab is placed). Concrete slabs with no vapor retarder are also a source of moisture transpiration from the earth. So, laying plastic sheeting (6-mil should be adequate) over either the dirt or concrete will go a long toward drying out the air in your basement. Wide sheets of plastic sheeting can be obtained inexpensively at lumber suppliers and home centers. When placing it, lap it up onto the sidewalls and throw dry sand onto it in the corners to create a reasonably good seal to the concrete. Cutting down on water vapor transmission from the crawl spaces will reduce the amount of work the dehumidifier has to do to dry out the air. Because dehumidifiers are quite expensive to operate, this should result in a lower electrical bill. With the crawl space problem addressed, you can turn your attention to the main basement walls and floor. Yes, TSP and water--with some chlorine bleach added to kill mildew and mold spores--will clean and freshen up those areas. It would be a good idea to wait until summer to do this job though. You'll be adding a lot of water to the air, and opening the door and using fans will help to dry out the basement. Once the concrete is dry, it would be a good idea to paint the walls with a couple of coats of "waterproofing" basement paint. One popular brand is DryLok. Paints of this type can significantly reduce water vapor transmission from the soil outside--again, reducing the overall humidity level in the basement. That, in turn, creates a dryer environment in which mildew and mold growth is not supported. As to who does this type of work, you might call your local Homebuilder's Association for references to a handyman type service or a painting company.

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