Definition: Mildew is a fungus (mold) that grows on many exterior painted surfaces, as well as on interior bathroom walls and other humid or poorly ventilated interior areas. If not corrected, painting over mildew will continue eating the existing paint away, causing eventual paint failure in the affected areas. There is no way to absolutely prevent mildew growth, however, it maybe controlled if the proper precautions and recommendations are followed.
* Failure to prime a bare wood surface before applying the paint
* Painting over a surface previously infected with mildew
* Excess humidity or other moisture problems
Painting over Mildew Solutions:
* First, to determine if the problem is mildew, apply a few drops of bleach to the surface. If the dark color bleaches out in a few minutes, it is likely mildew, as dirt or other contamination would not be affected.
* Locate and correct any sources of moisture accumulation or excess humidity.
* Protect all plants and shrubs with dropcloths before cleaning the surface.
* Clean the surface with a commercially prepared mildew remover or use a homemade solution of one quart liquid chlorine bleach, three quarts warm water and 1/4 cup ammonia-free liquid dishwasher detergent.
* Rinse the surface and surroundings thoroughly with clean water.
* Allow the surface to dry completely before painting over mildew.
* Use an appropriate primer and then apply a high-quality paint in the desired finish.
For More Information: Painting over Mildew