Ventilate crawl space to control moisture

Q. Our home has a reasonably dry cellar. In every humid weather, however, we do have condensation on the walls, especially at a corner which borders a crawl space. Little puddles of water accumulate on the floor in that area only. Would opening a window in the crawl space prevent the moisture? Should the window be open all the time or just in the summer? Should the window be shut when it rains? Also, can you suggest a sealer to apply to concrete walls that does not have a strong odor? C. M. Oteri Wellesley, Massachusetts

A. Ventilation in the basement will reduce the condensation caused by high humidity. By all means, open the window in the crawl space. Add some windows or foundation vents to not only increase the ventilation but develop it crosswise.

If this natural ventilation fails to control the condensation, install a fair-sized fan to mechanically compel frequent changes of air. Let the process continue even on rainy days.

If the moisture occurs in the wintertime, continue to ventilate as needed but perhaps reduce the frequency of air change by closing some of the windows and vents. As an alternative, install a dehumidifier. Experiment until you find the right combination.

Now, as to the kind of odor-free sealer for the concrete basement walls:

If the purpose is to waterproof the concrete from the migration of water from the outside, apply a proven product for below-grade waterproofing which is equal to Sealwall, Thompson Water-Seal, or Thoro-Seal.

Take a whiff of the uncapped product before application to assure you of its inoffensiveness. Explicitly follow the manufacturer's recommendations.

If the purpose of the sealer is to make the concrete washable or to color it, apply a regular masonry or concrete sealer and paint readily available at your local paint store.

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