What is Black Efflorescence?

Black Attack, also referred to as black efflorescence or desert varnish, is the unpredictable sporadic darkening of concrete, clay and natural stone. It usually occurs within six months of installation and is not easily removed either with solvents or by physical means. The phenomenon is all around us – it can occur on pavers, bridges and buildings.

Black efflorescence on a concrete bridge

The formation of efflorescence on a site (black and white) is linked to the earth’s water content beneath the paving. In areas where high water tables exist or where moist clay soils are prevalent, efflorescence is usually a common occurrence. Black efflorescence is usually common to specific geographical areas. A neighbour’s paving and adjacent concrete structures would give you an indication of the potential of your paving being affected by efflorescence. Many studies have been conducted and the precise cause of this phenomenon is still not well understood. It has been found however that there does seem to be a correlation between black efflorescence and the moisture of the installed area. In the short term, the only solution is to replace the affected pavers and ensure adequate drainage of the subbase during installation.

Over time and as the pavers wear the discolouration might fade and blending with other pavers will improve. There are other kinds of discolouration that could be mistaken for black efflorescence namely: mould, algae, tyre rubber and staining from bedding sand.