Mildew is a black or brown fungus that can grow on, and disfigure exterior surfaces, including paint. While it is not possible to guarantee a 100% mildew-free paint job, especially for a long period of time, there are some precautions that can help significantly in reducing or avoiding mildew growth on a paint job.
Mildew is not caused by paint. It grows on many types of surfaces. Mildew discoloration, which resembles dirt, is due to fungi feeding on oil contained in oil paints or on protein thickeners used in latex coatings. They also feed on nutrients in the surface material, underneath the paint film.
Mildew Identification & Control
Mildew requires three conditions for growth: food, moisture, and warmth. Removal of these three requirements will inhibit or stop its growth. Mildew feeds on organic material that is present in abundance; therefore, food for mildew growth is everywhere. Moisture is the most important single factor in the growth of mildew, which can lie dormant for years if kept dry. For this reason, the discoloration is usually found in damp, dark places.
Dirt and mildew often look alike. Usually dirt can be removed with soap and water while mildew stains will be unaffected by soapy water. To identify mildew, drop a small amount of household bleach on the surface. If the stain is mildew, the bleach will destroy the fungus and whiten it. If it is simply dirt, the stain will remain.
The mildew must be removed prior to repainting or the new coat will soon show signs of discoloration. Scrub the surface with a solution of 1 cup of (non-ammonia) detergent, 1 quart of household bleach and 3 quarts of water using a medium soft brush. In severe cases use
2 quarts of bleach and 2 quarts of water. Rubber gloves, eye protection, and other protective clothing is recommended, as the solution can irritate the eyes and the skin.
The area should then be rinsed completely and allowed to dry. Repaint as soon as possible with a paint that contains mildewcides, such as Diamond Vogel Permacryl Exterior Acrylic Latex. For maximum protection, a primer with mildewcides such as Diamond Vogel Sure Grip Exterior Acrylic Latex Primer is also recommended.
For best results, repaint in a dry season. When applying the new coating, use a generous amount, since a thin coat allows fungi to penetrate more easily. Thick shrubbery in front of the area can block out sunlight and allow dampness to create a mildew-growing problem. Keeping shrubbery thinned would help by allowing air movement in the area.
For further information on identifying and controlling mildew, contact your Diamond Vogel representative.