Efflorescence is
the visible white dusting that appears on the
surface of concrete during hydration. The best
way to deal with efflorescence is to learn more
about it. Our goal is to make you more aware of
the reasons it appears, how to reduce it and
minimize its effects.
This film of
calcium and soluble salts on the surface is a
common problem and tends to be more noticeable
with colored concrete. Although color is often
blamed for efflorescence, pigments do not
contribute to the formation of efflorescence.
Typical problems stem from pouring at a high
slump, excessive bleed water, adding water to
the surface while finishing and inconsistent
sub-grade.
Important: Brooming concrete with a
wet broom is another contributor to
efflorescence, one that is often overlooked.
As concrete
cures, it hardens. So does the film of
efflorescence on the surface, becoming difficult
to remove the older it gets. In favorable
conditions efflorescence can be removed after 24
to 48 hours with water and a push broom or
pressure washer. A pressure washer (1500 psi
medium tip) is preferred because its output is
1.5 gallons per minute. Water from a garden hose
pours out at about 5 gallons per minute. This
could result in re-hydrating your slab and
taking longer for it to dry. In cool conditions
this could start the efflorescence process all
over again.
After one to
two weeks, cleaning with a proprietary acid
solution may be needed to aid in the removal of
efflorescence. After two to three weeks, a light
sandblasting is one more option.
Another method
is to acid wash the surface, before sealing.
