Black, grey or brown stains on the painted surface.
Causes:
Mould frequently occurs in humid areas or in areas where there is little or no sunlight (particularly on northern sides and eaves);
Low quality paint that includes little or no mould protective agents;
Painting the foundation without previously removing mould.
Solution:
Apply drops of bleach on the mouldy area. If the stain disappears, the most probably cause is mould. Clean the mouldy areas with a special mould prevention agent. Then carefully clean the surface with water. Treat new wood with a wood impregnating agent and paint the entire surface with a good outdoor paint.