What is efflorescence?
Efflorescence is a natural phenomenon and can occur with all cement based products, as well as other paving products. It may appear randomly and will possibly appear more pronounced on coloured paving. The white bloom may give the impression that the colour of the paving is fading but, when wet, you will find that the efflorescence vanishes and the paving returns to its original shade. The white bloom will often return again when the paving dries. Be reassured that efflorescence has no detrimental effect on the performance of the paving and will generally disappear with time.
How does efflorescence occur?
All concrete products contain cement which produces water soluble calcium oxide (lime). Concrete paving stones contain millions of tiny invisible pores; when moisture penetrates into these pores - either from rain, dew or condensation - it dissolves part of the lime to make calcium hydroxide. When the paving dries out, the calcium hydroxide rises to the surface and reacts with the carbon dioxide in the air, sometimes leaving a white bloom of calcium carbonate once the water has evaporated.
Will efflorescence disappear naturally?
– Yes. The efflorescence action is arrested by carbon dioxide reacting with calcium oxide within the pores of the concrete, so blocking them. The efflorescence itself is then, over a period of time, either converted back to soluble salts and washed away by rain or simply disappears through the action of trafficking, snow or ice. Once the efflorescence has disappeared naturally it does not usually recur. It is therefore not necessary to replace the paving or to take other measures against efflorescence.
How long will efflorescence last?
This is difficult to predict as factors such as climate conditions, location and aspect (damp/shady or open/sunny) are variables which can affect the extent of the phenomenon. However, on average, it can take from 12 months to two years to disappear.
Can efflorescence be removed without the wait?
Efflorescence may be removed with a proprietary brand patio cleaner, but be sure to follow all the manufacturer’s instructions as incorrect cleaning can result in damage and discolouration of the paving surface. Efflorescence may reappear if there is free lime within the paving or the pores have not yet been blocked. Ideally, the new paving should be left several months to allow as much of the lime as possible to leave the concrete to minimise the risk of recurrence.
Bradstone cannot accept responsibilty for the effect of efflorescence which can be characteristic of all good quality products with a high cement content.