General Information
Efflorescence
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 colored
paving. The white bloom may give the impression that the color 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 discoloration 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 minimize the risk of
recurrence.