Efflorescence

Efflorescence is a Natural Phenomenon. It is the name given to crystalline or powdery deposits, normally white, which form on the surface of in-situ concrete. Precast concrete, concrete blockwork and brickwork.

Primary Efflorescence

Occurs in the time from when the product is in the saturated state to when it is dry, and normally immediately after the product has set.

Secondary Efflorescence

Occurs at a later stage, when the product is in service and has been exposed to wet humid conditions.

Conditions where condensation or rising ground water can permeate the concrete over an extended period, followed by slow drying, this could promote the formation of efflorescence.

Prevention

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.

Mechanism

Concrete products are made form natural occurring materials, mixed with water. Once a concrete product is made and subjected to weathering, moisture penetrates into the pores of the product and dissolves an element of lime contained within. Under damp conditions this solution, calcium carbonate crystals which are white in appearance, migrates to the surface and usually forms an extremely thin layer giving the effect of efflorescence.

Efflorescence will be eroded by rain, which is slightly acidic. As nature causes the problem, nature and time hold the cure.

Removal

It can be removed mechanically by dry brushing or shotblasting the surface or by washing with dilute phosphoric acid, dilute hydrochloric acid or a commercially available masonry cleaner. With acid treatment it is recommended that the surface is first soaked with water to prevent acid penetration and is thoroughly washed after treatment.

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 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.

Efflorescence is a natural phenomenon and one that does not affect the durability and performance of the concrete in question.