Paint With Confidence

Exterior Common Issues & Solutions


Text & image courtesy of the Rohm & Haas Paint Quality Institute


Black, gray or brown areas of fungus growth on the surface of paint or caulk.

Possible Cause

  • Forms most often on areas that tend to be damp, and receive little or no direct sunlight (walls with a northerly exposure and the underside of eaves are particularly vulnerable).
  • Use of a lower quality paint, which may have an insufficient amount of mildewcide.
  • Failure to prime bare wood before painting.


Test for mildew by applying a few drops of household bleach to the discolored area, then rinse; if it disappears, it is probably mildew. Remove all mildew from the surface by scrubbing with a diluted household bleach solution (one part bleach, three parts water); wear rubber gloves and eye protection. Power washing is also an option. Rinse thoroughly, prime any bare wood, then apply one or two coats of top quality exterior paint, which typically contains more mildewcide than economy products.