Correctly identifying a mess is the key to successful clean-up and prevention. Brick walls and walkways usually develop a white, chalklike appearance for three reasons: they were used for drawing, mould has grown on the surface or efflorescence has caused salt build-up. Identify the problem by examining the brick itself: if the white powder follows distinctive lines, it is probably chalk. Patchy areas of white and other colours indicate mould, while efflorescence has a distinct particulate appearance.
Put on protective items, such as a breathing mask, gloves, boots, trousers and long-sleeved shirt.
Scrub the white residue with a dry, stiff brush.
Hose down the wall with a concentrated stream of water. Scrub with a wet brush.
Clean drawing chalk with a mild detergent. Apply mould killer to mildew and other fungal growths. Use efflorescence cleaner to diminish the appearance of mild cases, in which crystals have not formed. Follow the instructions provided if using a commercial cleaner.
Rinse thoroughly and scrub.