Efflorescence is a deposit of
salt left on the surface of concrete or masonry by the evaporation of moisture,
which brought if from within the structure. Efflorescence is unsightly but
harmless unless it accumulates within the pores of a material. Such
accumulation can disrupt the surface. Leaching of salts from within concrete or
masonry is the most common cause of efflorescence. However, salts in soil which
are in contact with a concrete or masonry structure unprotected by a moisture
barrier is seen to migrate upward as much as 2 ft. and sometimes more and get
deposited on the surface. A reaction can also form efflorescence. For example,
calcium hydroxide in concrete and masonry can combine with carbon dioxide in
the atmosphere to become calcium carbonate.
Methods for removing
efflorescence:
Most efflorescence can be
removed by one of the following method:
·
Scrubbing with a dry brush.
·
Scrubbing with water and a brush.
·
Light waterblasting.
·
Light sandblasting and hosing with clean water.
However, some salts become
water insoluble shortly after reaching the atmosphere. Efflorescence of these
salts can be removed with a dilute solution of acid. Suggested solutions
include:
·
One part hydrochloric acid (muriatic acid) in 9
to 19 parts water.
·
One part phosphoric acid in 9 parts water; or
·
One part phosphoric acid plus one part acetic
acid in 19 parts water.
The solution should be tested
on a small, inconspicuous area to determine whether there will be adverse
effects.
Preventing recurrence of
efflorescence
To prevent recurrence of
efflorescence on concrete and masonry surfaces, it is necessary to keep water
absorption low and to prevent moisture movement through the mass.
- Use a moisture barrier, sealer, membrane, impermeable overlay on exterior walls or apply vapor proof paint to interior surfaces.
- Use wide, overhanging roots and sheds to protect walls from dampening due to rainfall.
- Locate pipes, taps, fittings or other water resources away from walls so that they are not subject to un-necessary wetting.
- Install drains with proper levels to reduce high groundwater table.
- Use epoxy injection or chemical grouting at visible cracks or joints subject to efflorescence.
