Possible Causes



• Damp areas that receive little or no direct sunlight (thus, such areas as walls with a southern exposure and the underside of eaves are particularly vulnerable)
• Use of a lower quality paint with an insufficient amount of mildewcide
• Painting over a substrate or coating on which mildew is present
• Failure to prime bare wood before painting
  
  
  Solution
  
  
  
• First, make sure that the discoloration really is mildew, and not just dirt. Apply a few drops of household bleach to it, wait five minutes, then rinse. If the dark colour disappears, the discoloration is probably mildew.
• Remove all mildew by scrubbing with a diluted household bleach solution (one part bleach, three parts water). Be sure to take the proper safety precautions - wear rubber gloves and eye protection. Leave the bleach on the surface for several minutes, then rinse.
• Next, thoroughly clean the surface with a detergent solution to remove dirt and other organic material on which mildew can feed. This can be done by hand or with a pressure washer.
• Rinse again. When the surface is dry, apply one or two coats of an ultra premium quality acrylic paint - this type of paint contains extra mildewcide and will resist mildew better than oil-based or lower quality alkyd paints.

This information is provided by the Rohm & Haas paint Quality Institute, www.paintquality.com.au