Common Paint Problems

How-To

Detailed solutions from PPG Porter® to the most common paint problems faced by both painting professionals and do-it-yourselfers.

Exterior

Mildew:

 Brown or black blotches that form on the surface of paint or caulk due to the presence of fungi that feed on the paint film and other organic matter.

Possible Causes

  • * Damp areas that receive little or no direct sunlight (walls with a northern 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

Solutions

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, and rinse. If the dark color disappears, the discoloration is probably mildew.

Remove all mildew by scrubbing with a diluted household bleach solution (one part bleach, three parts water). Leave the bleach on the surface for several minutes, and rinse. 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 power washer. Rinse again. When the surface is dry, apply one or two coats of top-quality acrylic latex paint, which contains extra mildewcide and resists mildew better than oil-based or alkyd paints.

Porter® System Recommendations

  • Finish: Two or more coats of Super Premium PORTERSEPT Satin Acrylic Exterior House & Trim Paint No. 3939 Series