Black, grey or brown spots on the paint surface.

Due to:

1. Surface dampness, or surface receive little or no direct sunlight.
   
   
2. Use of lower quality paint.
   
   
3. Failure to prime wood surface before applying the top coat.
   
   
4. Painting over substrate where mildew has not been removed.

Recommendation:

1. Use few drops of household bleach to identify whether the black area is mildew or dirt. If it is mildew it will discolour. Alternatively, use detergent and water to remove the black area. If mildew is present, it will not wash away.
   
   
2. Remove all mildew with diluted household bleach (1 part bleach, 3 parts water). Leave for 5-10 min to kill all the mildew spores. Scrub and wash away with detergent and clean water. Allow the surface to dry thoroughly before painting. After the surface preparation, paint with good quality top coats.
   
   
3. Install exhaust fan in high moisture areas to keep good ventilation.