What is the white, powdery substance on my bricks?
Efflorescence is a powdery deposit of salts which forms on the surface of bricks and paving. It is usually white but efflorescence can be yellow, green or brown.
Efflorescence does not in any way influence the structural strength of clay bricks or pavers. Roman buildings that have been standing for 2 000 years can show efflorescence
A temporary efflorescence is particularly common on new brickwork and paving as soluble salts are dissolved and transported to the surface of the brickwork and paving by water. The efflorescence on new well fired brickwork and paving may be unsightly, but it will not cause damage unless the brickwork and paving are under-fired or soft-fired, in which case serious efflorescence can cause flaking of the surface of the brick or paver.
Efflorescence can occur from a variety of sources. Besides the brickwork, soluble salts can originate from the sand, mortar and the water used. Ground waters that are naturally salt-bearing can be drawn into the base of the brickwork and paving.
The best removal method is simply to brush off the deposit with a stiff dry bristle brush after the wall has dried out. Collect the removed salts with a dust pan or a vacuum cleaner to prevent the salts re-entering the brickwork. Wetting the wall by methods such as hosing usually dissolves efflorescence back into the brickwork, allowing it to reappear again when the wall dries out.
Acid or alkaline treatments are not recommended as they do more harm than good because they add to the total salt content.
High pressure washers can remove the surface of the brick, resulting in serious deterioration in the long term.
Dries V of Cermalab