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www.mcsmag.com AUGUST 2020
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waterproofing functions take place in
a quicker, more cost-effective manner
because labor associated with a surface
treatment application is eliminated.
Procedural sequence for addition will
vary according to the type of batch, plant
operation, and equipment. For most
mixtures, the dosage rate of integral
crystalline waterproofing admixture is
1-2 percent, based on the amount of
cementitious material in the mix.
SILANE & SILOXANE WATER
REPELLENTS
The use of a waterproofing coating can
be undesirable in some cases due to
aesthetics or the desire for a simpler
application process. Certain concrete
applications do not need to be fully
waterproofed, but instead can function
properly with a water repellent treatment,
such as silane and siloxane.
Derived from the silicone molecule,
silane and siloxane create an envelope
of protection that can extend the life of
substrates even in difficult environments.
Both are UV stable, reduce efflorescence
and freeze-thaw damage, are highly
wear-resistant, and permit the substrate
to breathe—in turn allowing interior
moisture vapor to escape. Water
repellent sealers can be used to impart
water repellency to a variety of porous
substrates, including poured-in-place or
pre-cast concrete.
Silane and siloxane sealers reveal little
to no change in the appearance of the
substrates to which they are applied.
There is no gloss, color change or hiding
of the substrate underneath. This is
important when water protection is
required for architectural finishes where
a waterproofing coating would hide the
decorative feature.
While silanes and siloxanes provide
excellent water repellency to surfaces,
each has its own performance differences.
Silane-Based Water Repellents.
Corrosion and scaling due to exposure
to salt spray and chemical deicing
products is a primary cause of concrete
deterioration. Silane-based sealers
provide an extremely effective solution
to prevent deterioration from water and
salt. Silanes penetrate deep because
of their extremely small molecular size
and ability to chemically bond with silica
to form a permanent attachment to the
water-repellent molecule. This creates
a deep hydrophobic layer that prevents
water and waterborne contaminants
from entering the substrate and
causing premature deterioration, while
simultaneously leaving the surface with a
completely invisible finish and providing
a chemical “screen” that prevents
chloride ions from reaching embedded
steel in concrete.
Once applied, silane water repellents
penetrate into the substrate and react
chemically with calcium hydroxide to
form a hydrophobic, water-repellent resin
within the pores and on the surface. In
order for this chemical reaction to take
place, the substrate must be alkaline
(high pH) and contain calcium hydroxide.
Because silanes do not change the skid
or slip resistance of concrete, they are
ideal for surfaces such as walkways,
bridges, and roadways. Silanes are not
effective in sealing other substrates such
as natural stone, clay, brick, or wood.
Because silanes consist of smaller
molecules than siloxanes, they will
typically penetrate deeper than siloxanes
and thus perform better on dense
surfaces such as poured-in-place and
pre-cast concrete. A consequence of this
molecular size is that silanes are quite
volatile. Therefore, the solids content
of a silane water repellent should be
high enough to compensate for the
evaporation of reactive material during
application and curing.
Siloxane-Based Water Repellents.
Siloxanes have a slightly larger molecular
structure and are somewhat effective
on substrates up to medium porosity,
such as heavyweight, smooth-faced, and
concrete block. Despite being closely
related, the siloxane-based chemical
composition does not encourage rapid
evaporation. The solids content and cost
of a siloxane-based sealer is typically
lower than that of silanes.
Unlike silanes, siloxanes are not
dependent on substrate pH to react. They
can react with atmospheric moisture, as
well as any moisture in the substrate,
to form the hydrophobic resin. For this
reason, siloxanes are ideal for treating
non-cementitious building materials such
as brick, stucco, and stone.
CLOSING THOUGHT
By using the latest technologies,
concrete contractors can combat water-
related damage and ensure optimal
concrete protection.
about the author
Jennifer Crisman is director of marketing
services at The Euclid Chemical Company, a
leading manufacturer of specialty concrete
and masonry construction solutions. A
20-plus-year industry veteran, Crisman
manages the marketing communications
activities for Euclid’s expansive line of
admixtures, fiber reinforcement, concrete
repair products, flooring materials, and
decorative concrete systems. For more, visit
www.euclidchemical.com.
