Efflorescence is a calcium or alkaline salt
which forms as a blotchy, powdery or crystalline deposit on the
surface of masonry walls and concrete products. It is due to
moisture entering through the walls or the surface of the Cast
Stone, coming with the calcium hydroxide in the cement and bringing
the hydroxide to the surface in a solution which forms crystals
when it combines with the carbon dioxide in the air.
Efflorescence is unsightly and is usually
a source of disagreement between builders and architects as to
why it occurs and what should be done about it when it appears.
It is not always possible to predict whether masonry will have
efflorescence. Soluble salts and moisture must be present for
efflorescence to occur. These salts may be present in the concrete,
mortar, brick, or Cast Stone. They may be carried into the wall
with rainwater or absorbed by ground water. Planter areas and
water table sections must be properly damp proofed to prevent
wicking of ground water. Improper ground storage is a common
cause of salt contamination. There is some evidence which suggests
that salts can be interjected with admixtures, de-icers or with
cleaners. While acids are frequently used to remove efflorescence,
they can contain chlorides which contribute to efflorescence.
This is one reason why many buildings show signs of efflorescence
shortly after wash down.
ASTM C 67 - Standard Test Methods of Sampling and Testing
Brick and Structural Clay Tile - includes a wick test for ascertaining
whether a brick is liable to cause efflorescence. Small specimens
or cubes either molded or saw cut from Cast Stone may be evaluated
by this test.
Common installation problems which can cause or enhance efflorescence
include the improper use of through-wall flashing, lack of sufficient
weep holes, use of Cast Stone without ventilated wythe, use of Cast
Stone below grade or at planter type areas without proper moisture
barrier, failure of joint materials which allow water entry and
the use of hard mortar joints where sealant joints should be used.
Soffit stones are particularly susceptible to efflorescence from
masonry walls above and should be designed to prevent from becoming
the "gutter" of the wall.
Most efflorescence is temporary and, as such, should be left alone. It most commonly
occurs shortly after building wash down and during the fall and winter months
when vapor transmission slows down and masonry stays damp for extended periods
Acid rain is a natural remover of efflorescence since most salts are highly soluble
If necessary environmental considerations are taken, a dilute solution of muratic
acid (5 - 10%) will remove common efflorescence as well as any carbonate of
lime which may be present. Manual washing can often draw additional salts to
the surface and repeat washing may be necessary, but when all of the salts have
come to the surface naturally and been washed off, there will no more trouble
from this cause.
Custom Cast Stone
734 East 169th Street • Westfield, Indiana 46074
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