Mildew

Causes

• 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

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.
• Use an appropriate primer and then apply a high-quality paint in the desired finish.

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.
 
Notes

Dunn-Edwards uses mildewcides in all exterior paints to resist new mildew growth. In addition, a fungicide or mildewcide may be added to the primer and paint if extra protection is desired.