Efflorescence is a natural phenomenon causing a “whitish” coating to appear on the surface of cement and clay pavers.
It is the formation of salt deposits on or near the surface of the pavers.
This white haze is often blamed on the manufacturer or contractor but there is no way either of them could guarantee that efflorescence will not occur.
This is nature at work and beyond the control of the manufacturer, contractor or homeowner.
Efflorescence happens when salt deposits from the cement used in concrete pavers dissolve in water and rise to the surface and evaporate, leaving a coating of the salt - a “whitish” film on the surface of the pavers.
Efflorescence originates not only from the pavers but also the aggregates used in installation and the subgrade beneath the pavers.
It brings out salts that are not ordinarily part of the cement stone and thus is not a structural problem but an aesthetic one."
The water soluble salts are found in cement, clay bricks and sand and dissolve in moisture either present in the building material (primary efflorescence) or from rainfall, groundwater or other sources (secondary efflorescence). The more porous the material, the easier it is for the salts to travel to the surface.
It will disappear over time –although no-one can say exactly how long it will last. It may be a few weeks or a few months. The worst case scenario is about 2 years.
In many instances rain will simply wash away white efflorescence.
Efflorescence does not cause any long-term harm to the paving.The effects are purely aesthetic, and it does not affect the strength or durability of concrete.
The best means of treating an affected area is by allowing natural weathering to take place.
For the technically minded here is a more detailed, scientific description of what is happening.
As the cement and weather chemically react together, Calcium Hydroxide is produced. and as the concrete dries it reacts with carbon dioxide in the atmosphere to produce Calcium Carbonate – the discolouration you see on the pavers.
Efflorescence on concrete pavers is Calcium Carbonate with lesser quantities of other carbonate, sulphate, and chloride salts while for clay pavers, it is Sodium Chloride – or table salt – together with sulphates and some carbonate.
Calcium Oxide, Carbon Dioxide, and Hydrogen Oxide (water) are the three main ingredients.
These chemicals interact with certain weather conditions that can speed up or slow down the chemical reactions.
Most of the Calcium Oxide will come from the paving itself, it may also be present in the sub-base - especially where concrete is used.
Water comes from above (rain or dew ) or the ground below or manmade sources of water such as sprinklers or hosepipes.