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It is very difficult to obtain all these qualities. Thus,
good impermeability to water is always accompanied by reduced
permeability to water vapor. Products are nearly always the
result or a more or less judicious compromise.
Furthermore, water repellents are not "miracle"
products that help to solving all problems. For example, a
water repellent treatment will not make string course stone
resistant in the long term if its quality is too low.
Water repellent products marketed for rock are designed to
make surfaces impermeable without significantly changing the
appearance. Penetration takes place over a few millimeters,
depending on the rock and the product. They belong to one
of seven categories of the following chemical compounds: siliconate,
silicone, silane, siloxane, organometallic, organo-fluorinated,
acrylic and vinylic compounds.
Experience has shown that there is no product that universally
combines all quality performance criteria on all substrates.
Durability is strongly influenced by the concentration and
nature of the solvents.
The search for non-noxiousness (excessive reduction of evaporation
that causes alteration of some fine-pore structures) is often
the essential factor to be considered in priority. The best
solution can only be chosen after experimentation, unless
precise references are available.
IMPORTANT : it is strongly
recommended that horizontal parts should not be made water
repellent, except for special cases.
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