"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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