All concrete products may suffer the temporary phenomenon of efflorescence, caused by the migration of soluble salts to the surface. Efflorescence can sometimes appear as white powder, or just an apparent lightening or fading of colour. This is caused by the migration of soluble salts to the surface. The most common being calcium hydroxide which reacts with atmospheric carbon dioxide to form calcium carbonate, a white deposit of low water solubility becoming apparent as the surface dries.
Calcium Hydroxide Ca (OH)2 + Carbon Dioxide (CO2) + Calcium Carbonate (CaCO3) + Water (H2O)
Removal of Efflorescence
Ideally it is better to let the phenomenon to disappear naturally, but it can be removed chemically by using proprietary acid washing agents or brick/patio cleaners in accordance with manufacturers instruction. Care must be taken and protective clothing must be worn.
However, both techniques can alter the appearance of the concrete by changing the surface texture and may also damage the concrete surface.
Before attempting to remove the efflorescence by these techniques it is recommended that trials should be carried out on samples, or a limited area, in order to assess the effect on the appearance.
It is not possible to predict precisely when, or if, efflorescence will occur as relatively minor changes in the quality of the concrete, the curing conditions and the environment can cause its formation.
Efflorescence is a natural phenomenon and one that does not affect the durability and performance of the concrete in question.