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The Treatment of Efflorescence

An explanation of the elimination of efflorescence on concrete pavers


By closely observing the precautions mentioned beforehand, it is generally possible to prevent, to a large extent, the occurrence of efflorescence.

In some cases, where this has not been successfully despite taking the necessary care, or where severe secondary efflorescence has appeared over the course of time, it may be possible to remove lime deposits.

In situations where paving units have already been laid, this can be done by lightly shotblasting or sandblasting the units insitu.

In this way a thin layer of concrete from the surface can be removed to expose the clean uncontaminated concrete below the surface.

This process is however very difficult to control and not generally recommended as it does in fact erode the surface of the concrete, which in the case of a non-exposed aggregate type product, would be unacceptable.

An alternate technique, but again very difficult to control, is to wash the surface of the pavement in question with a dilute mixture of hydrochloric acid. The process here is firstly to thoroughly wet the paving area in question with clear fresh water and ensure that it is totally saturated.

In this way the pores of the concrete fill up with water which prevents the mild acid solution from penetrating too deeply into the stone and causing additional efflorescence in the form of water-soluble salts. Then apply a dilute solution of water to hydrochloric acid (15 parts water to 1 part acid) to the paving surface preferably brushing at the same time. After being allowed to take effect for approximately 10 seconds, rinse off the acid wash with plenty of clear fresh water.

With this acid treatment, just as with sandblasting or shotblasting, a thin layer of the concrete paving surface is removed, thus appearance of the paving in question can be changed if not carefully controlled.

It must be pointed out that the inorganic pigments suitable for the colouring of concrete will survive the effects of a light controlled acid wash without damage, although a slightly darkened appearance of the colour may eventuate. This change in colour is more likely to be as a result of the removal of the light (white) efflorescence on the surface, rather than a change of the inorganic pigment.

However, in most cases, even if no attempt is made to remove the efflorescence, it is more than this calcium hydrogen carbonate is easily washed away with rainwater.

Depending on weather conditions, this process may however take up to two years to complete. It must be noted that efflorescence may also be attributed to the material on which the concrete units likely that it will disperse after a period of time in line with the chemical reaction: CaCO3 + CO2 + H2O = Ca(HCO3)2 In other words, soluble calcium hydrogen carbonate is gradually formed from the insoluble calcium carbonate under the continued influence of carbon dioxide and water, and are in contact with, particularly in the case of the concrete segmental paving. Concrete paving is usually laid on a bedding of sand, and naturally occurring salts within the bedding sand can and will, through the action of capillarity migrate to the surface of the paving and be deposited on the face of the unit. Additionally, when paving units are laid on a bed of concrete mortar, calcium hydroxide emitted from the curing mortar bed can migrate through the paving surface.

The process and types of efflorescence are exactly as detailed previously and if required, will need treating as described.

Summary


Efflorescence can be described as a "passing nuisance". Invariably , these unsightly deposits will be blamed on the concrete manufacturer, unjustifiably in most cases because this so-called efflorescence is a natural phenomenon.

Efflorescence should be seen for what it is, a sign of life from a product made of natural raw materials.
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