Thanks for the information. I was a bit worried since we live within a few
miles of three of the top superfund sites, at least two of which can't be
cleaned up and have been cemented over.
Shell
wrote in message
...
"Efflorescence
Water that moves through a material in a liquid state can also produce
many harmful
effects. The most obvious is the efflorescence that often disfigures the
face of a
building. Migrating water dissolves salts from some position inside the
material and
then deposits them on the surface as the water evaporates. Usually this
effect is not
destructive but merely disfiguring. If a vapour-permeable but
water-repellent
membrane is applied to the outer face of the wall, however, the water may
be caused
to evaporate from behind it, so that the salts are deposited behind the
surface layer
and the resulting force of crystallization can cause the skin to spall.
The subject
of efflorescence has already been dealt with at considerable length in CBD
2 and need
not be examined further here. It should be noted, however, that the
spalling produced
by the crystallization of salts behind the surface of the material is very
similar in
appearance to that produced by frost action, and in many cases it is
difficult to
determine which mechanism has caused it. Surface treatment of masonry may
promote
further complications if it restricts the escape of vapour that is
migrating from
inside the building. This vapour may be forced to condense behind the
surface and
lead to, trouble under freezing conditions.
Leaching
Liquid water moving through concrete and mortar can cause a steady
deterioration of
these materials by leaching out the calcium from the calcium silicate
bonding
materials. This action is most pronounced with soft or mildly acidic
waters such as
are found in reservoirs fed from swampy areas. Very often this water
percolates
through the dam at the level of the concrete lifts and runs down the
downstream face
where it evaporates, leaving a white deposit. A similar deteriorating
effect has been
seen in buildings such as paper mills where the high humidities cause
water vapour,
which passes into hollow concrete roof beams and condenses in the colder
upper parts.
The pure condensate may have absorbed carbon dioxide from the air and
become slightly
acidic. As the water migrates within the beam the calcium compounds are
dissolved
from the cement and in many locations have been left, after the drop of
water bas
re-evaporated, as stalactites of calcium carbonate. The undersides of such
beams were
seen to have no cementing material left and were covered with loose sand
that could
be brushed off by hand. Similar effects may be seen where rainwater
percolates
through concrete bridges and abutments and on the faces of buildings where
it has
entered behind facing stones and reappeared lower down, carrying with it
calcium
compounds from the mortar or backing concrete."
http://irc.nrc-cnrc.gc.ca/cbd/cbd030e.html
"Shell" wrote:
This is both on and off topic. First the off topic. Has anyone else
experienced a strange white stuff growing on thier concrete? It looks
like
a cross between a crystal and a fungal growth and shows up mostly on
polished concrete surfaces like garage floors where it eventually eats
into
the cement. I have no idea what this stuff is and I'm sorry I dont have
a
picture of it. It seems to grow mostly after the concrete gets damp or
wet.
Now the on topic. I would love to know what this stuff is and if anyone
might know how to get rid of it because it is now growing on a one of my
terracotta pots and I'm concerned for the plant in the pot.
Any advice or help or even just comments are welcome
Shell
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