Close up image of a surface that has black, gray or brown areas of fungus growth.

Mildew- INTERIOR/EXTERIOR

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

Causes

  • Use of a lower quality paint, which may have an insufficient amount of mildewcide.
  • Failure to prime bare wood before painting.
  • Painting over a substrate or coating on which mildew has not been removed.
  • Applying paint in a very thin coat.
  • Excess humidity and other moisture problems.

Solutions

  • 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) or a commercially-available mildew remover.
  • Rinse thoroughly, prime any bare surface with the appropriate primer, then apply one or two coats of high-quality exterior paint.

*CAUTION: Chlorine bleach must never be mixed with ammonia or with any detergent or cleaners containing ammonia. These mixtures will form vapors that can be harmful or even lethal. Gloves, goggles and protective clothing should be worn for protection.

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