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The growth of white crystals on the surfaces of brickwork and blockwork is called efflorescence and is a common problem particularly in high rainfall areas.

Efflorescence is caused by the presence of water-soluble salts which occur naturally in cement-water mixtures. The salts are brought to the surface of bricks or blocks as hydroxides when the bricks or blocks begin to dry. Once on the surface, the hydroxides react with carbon dioxide in the air and carbonate salts are formed.

If tackled before heavy deposits occur, its removal is relatively simple, often just scrubbing with a stiff brush whilst running water from a hose over the surface. If the deposit is heavier, or proves hard to remove, the wall should be watered down thoroughly (to prevent the penetration of acid into the bricks or the mortar joints) and a solution of hydrochloric acid (Muriatic acid or spirits of salts) diluted to one part acid to nine parts water may be used on the efflorescence.

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