Efflorescence: This is caused because of alkalies present in bricks. When bricks come in contact with moisture, water is absorbed and the alkalies crystallize. After drying, grey or white powder patches appear on the brick surface. The degree of efflorescence is given as: (a) NIL – When there is no perceptible deposit of efflorescence. (b) SLIGHT- Not more than 10% area of the brick covered with a thin deposit of salt. (c) MODERATE- Covering up to 50% area of the brick. (d) HEAVY- Covering 50% or more but unaccompanied by powdering or flacking of the brick surface. (e) SERIOUS- When there is a heavy deposit of salts accompanied by powdering and/or flacking of the exposed surfaces.