This manifests as black, grey, or brown markings on the surface of the paint or sealant.
- Areas that tend to be damp, or receive little or no direct sunlight. Bathrooms, kitchens and utility rooms, for example.
- Using a solvent-based paint, or lower-quality water-based paint.
- Failing to prime a bare wood surface before painting.
- Painting over a surface or coating on which the fungal contamination has not been removed.
Test for fungus by applying a few drops of household bleach to the area. If the markings are bleached away, they are likely to be fungal.
Treat the contamination with a fungicidal wash, or apply a diluted household bleach solution (one part bleach to three parts water). Leave it on for 20 minutes, applying more as it dries. Ensure that you wear rubber gloves and eye protection while doing so. Scrub and rinse the surface thoroughly, and repaint it using a top-quality water-based paint – cleaning it when necessary with a bleach or detergent solution.
Consider installing an exhaust fan (connected to a light switch) in areas of high moisture.