mildewBlack, gray or brown spots or areas on the surface of paint or caulk.

Possible Causes:

Forms most often on areas that tend to be damp, or receive little or no direct sunlight (e.g., bathrooms, kitchens and laundry rooms).

Use of an alkyd or oil-based paint, or lower quality latex paint.

Failure to prime bare wood surface before applying the paint.

Painting over a substrate or coating on which mildew has not been removed.


Test for mildew by applying a few drops of household bleach to the area; if it is bleached away, the discolorant is probably mildew. Remove all mildew from the surface by scrubbing with a diluted household bleach solution (one part bleach, three parts water), while wearing rubber gloves and eye protection. Rinse thoroughly. To protect against mildew, use a top quality latex paint, and clean when necessary with bleach/detergent solution. Consider installing an exhaust fan in high moisture areas.

(image courtesy of The Rohm and Haas Paint Quality Institute)