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What is efflorescence on block paving?

Efflorescence on block paving

Efflorescence on block paving

Efflorescence, or white bloom, is the name given to the white dusty patches which can appear on the surface of concrete block paving driveway or brick walls after a few weeks or months. It is a natural phenomenon and will normally occur on most cement based products early in their life.

It can appear randomly over the surface, concentrated in a few patches or can form a blanket over the entire block paved surface, and it normally appears more pronounced on coloured paving. Although efflorescence has no detrimental effect to concrete block paving, it does make it appear as though the colour is fading. When wet the efflorescence disappears, returning the block paving to its original shade, only for it to reappear as soon as the surface dries off.

Efflorescence is the source of many customer complaints as they assume that there is a problem with the manufacture of the block paving, it will however disappear with time.

What makes efflorescence appear on block paving?

All cement based products such as concrete block paving and the mortar between bricks on walls contains lime (calcium dioxide) which is soluble in water. If concrete block paving was magnified you would see that it contains millions of tiny holes or pores and when water enters these holes (from rain water, condensation or dew) it dissolves some of the calcium dioxide, to form calcium hydroxide.

Calcium hydroxide, when suspended in water is known as the milk of lime and when the surface of the paving dries out it allows the calcium hydroxide to rise to the surface. Here, it reacts with carbon dioxide in the air to form calcium carbonate – the dusty white powder you see on the now dry surface of the paving.

Does efflorescence disappear from block paving?

Without any interference, efflorescence will disappear given time, though many customers are so unhappy that there new block paving is spoilt in this way, will not have the patience to allow nature to take its course. The chemical processes described above slow down and eventually stop when carbon dioxide reacting with the calcium oxide, cause the pores within the block pavers to block up.  Efflorescence on the surface of the block paving is either moved on through pedestrian or vehicular use of the surface, or forms soluble salts which are washed away with rain (or water from the hosepipe of an impatient householder).

Climate conditions, location and the aspect of the block paved surface can affect how long it takes for efflorescence to disappear from a new driveway or patio area, but once it has disappeared, it will not normally reappear. And although it can take as much as a year or two for efflorescence to disappear completely, it is certainly no reason to consider replacing the concrete block paving. Indeed, no block paving manufacturer will accept responsibility for the formation of efflorescence as it is a natural reaction on all products containing a high content of cement.

How can I remove of efflorescence from block paving?

Proprietary brands of patio cleaner are available which claim to remove efflorescence but incorrect or over use can lead to discolouration of the block paving, which is normally irreversible. Once these cleaning agents have washed away, however new efflorescence will continue to form until all of the available calcium dioxide within the paving blocks has either been used up or the ‘pores’ have become blocked. The recommended action is to allow time to deal with the problem.