Patches of fungus growth on painted or caulked surface that appears to be gray, brown or black.
Causes
Damp areas receiving little or no direct sunlight are vulnerable to this condition. Some examples are the underside of eaves and walls that have a northern exposure.
Using paint of a lower quality because it might contain insufficient mildewcide content.
Not applying primer to bare wood prior to painting.
Painting on top of a substrate or previously applied coating without removing existing mildew.
Solutions
Test the area to determine if mildew is present. Apply a small amount of household bleach to the unidentified discolorations.
You can identify it as mildew if it disappears.
Wearing eye and skin protection, treat with a 3:1 solution of water and bleach. Let stand for 20 minutes, adding to the application as it dries out. After 20 minutes, scrub the area. Rinse thoroughly.
Brush on an exterior latex primer.
Then apply the highest quality exterior latex paint.
Use satin, semi gloss, gloss or flat paint depending on your preference.
Manifestations