If you’ve noticed black, grey or brown areas on your painted surface, chances are you’re dealing with a mould problem.

Possible Cause

Exterior mould is usually caused by moisture. It’s often found in areas that are damp, and receive little or no direct sunlight (the underside of eaves are particularly vulnerable). Mould is more likely to occur after use of a lower quality paint, failure to prime clean bare wood before painting, or if you’ve painted over a coating of mould without removing it.



First, test for mould by applying a few drops of household bleach to the discoloured area. If it disappears, it is probably mildew. Remove it by scrubbing with a diluted household bleach solution (one part bleach, three parts water). Be sure to wear rubber gloves and eye protection. Power washing is also an option. Rinse thoroughly then remove and source of moisture where possible. Prime the surface with Dulux® PRECISION® Stain & Mould Blocker then apply an exterior top coat, Dulux® Weathershield® is recommended.

More problem solving advice


Have you noticed that there are areas of denser colour or higher gloss where wet and dry layers overlap during painting?  For each problem you’ll find a guide to identifying it, its causes and solutions.

Cracking / flaking

Cracking or flaking is the splitting of a dry paint film. This is a problem that needs fixing as it can lead to complete failure of the paint. For each problem you’ll find a guide to identifying it, its causes and solutions.