problem solver mildew

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

Possible Causes:

  • 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).

  • Use of a lower quality paint, which may have an insufficient amount of mildewicide.

  • Failure to prime bare wood before painting.

  • Painting over a substrate or coating on which mildew has not been removed.


  • Test to distinguish mildew from dirt by applying a few drops of household bleach to the discoloured area; if it disappears, it is probably mildew. Treat the mildew by applying a mixture of water and bleach, 3:1, and leave on for 20 minutes, applying more as it dries. Wear goggles and rubber gloves. Then scrub and rinse the area. Apply an exterior latex primer, then a top-of- the-line exterior latex paint in flat, satin, semi-gloss or gloss finish, depending on the desired appearance.