Page 36 - Haddonstone
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7.5 Efflorescence
Rain Dampens Surface Efflorescence, also known as lime bloom, 7.5.2 Prevention
may appear as a white deposit covering
Slowly soluble salts dissolve part or all of the surface of products The risk of occurrence of efflorescence will
and migrate towards the containing cement. The result of light be reduced by protection on site before
surface as the stone dries deposits is the lightening of the surface and during installation.
colour the heavier the deposit the lighter
This leaves minute white/ the colour. Except in very severe cases 7.5.3 Treatment
colourless crystas at the surface the phenomenon disappears completely
(known as Efflorescence) when the unit is wet and reappears at it Whilst it is better to allow the phenomenon
dries out. The phenomenon is temporary to disappear naturally, it may, however,
and will, with time, disappear as a result of be removed chemically by using a
normal weathering. The length of time will proprietary acid washing agent (e.g. dilute
depend on many factors such as rainfall, hydrochloric acid). The product should first
atmospheric pollution etc. be thoroughly soaked with clean water
followed immediately by the application
7.5.1 Occurrence of the commercial acid washing material
(which is generally available from most
Efflorescence is a temporary, naturally builders merchants) in accordance with
occurring phenomenon that occurs to the manufacturer’s instructions and Health
a varying extent on all items containing and Safety Guidelines.
cementitious binders. Mortar is particularly
prone to efflorescence in the form of lime A small trial area in an inconspicuous
staining and this can contaminate other place is recommended to be treated
products (e.g. cast stone, bricks etc). prior to any major application. As the
efflorescence dissolves there will be some
It is formed by soluble salts from the frothing and once it has finished the whole
cement migrating to the surface where surface should once again be thoroughly
they react with the atmosphere to produce rinsed with clean water. In the vast
the white powder (calcium carbonate) majority of cases one treatment should be
known as efflorescence. Individual crystals all that is necessary, but in severe cases
are very small and are not firmly fixed to retreatment may be required.
the surface.
The cast stone manufacturer should be
The smallness of the crystals linked consulted before applying any chemical
with their optical properties causes compounds to its products.
them to become invisible when wet. As
they dry out they become visible and
are unchanged. Products are more
susceptible to efflorescence under damp
conditions as this aids the movement of
the soluble salts.
Efflorescence in no way affects the
structural integrity of the cast stone.
Optical properties conceal the
crystals when they are wet
