MO-02Check what you're dealing withFluffy black or green spots on the surface, worst on cold corners or behind bulky furniture, is usually condensation mould. A damp patch that stays cold and wet, or spreads up from the skirting, may be rising or penetrating damp instead. If it looks like that, or there's a musty smell with no obvious cause, get the source checked before you just clean and repaint over it.