Black, gray or brown areas on the painted surface.

Possible cause

  • Mould forms most often on areas that tend to be damp, and receive little or no direct sunlight (the underside of eaves are particularly vulnerable)
  • Use of lower quality paint
  • Failure to prime bare wood before painting
  • Painting over a substrate or coating on which mould has not been fully removed



Test for mildew by washing the surface with water, this will take away excess dirt. If this is unsuccessful in removing the discolouration, then follow with applying a few drops of household bleach to the area; if it is bleached away, the discolouration is probably mildew. 

Remove all mildew from the surface by scrubbing with a diluted household bleach solution (one part bleach, three parts water); wear rubber gloves and eye protection. Power washing is also an option.

Rinse thoroughly, prime any bare timber, then apply one or two coats of top quality exterior paint. Dulux recommends the Dulux Weathershield® range for exterior surfaces.

More problem solving advice


Development of a yellow cast in aging paint solvent-based enamels


Appearance of a denser colour or higher gloss where wet and dry layers overlap during paint application.


A rough, crinkled paint surface occurring when paint forms a 'skin'.