to Selley. In addition, penetrating
water-repellant treatments do not
lay on the surface but actually penetrate into the pores of concrete
and other cementitious substrates.
As such, they are not exposed to
the wear experienced by traditional
coatings. Typically, silicone-based
products have been in use successfully for over 20 years.
Silicone coatings and sealants
are more expensive than their
organic counterparts, though.
“We believe that the significantly
extended performance window allows for significant cost savings on
maintenance and repair. The cost
of a project over the full lifetime of
a silicone-based coating, therefore,
is actually lower than if a shorter-lived organic formulation is used,”
comments Kimberlain.
One approach that some companies are taking is to create blends
of organic polymers with silicone-based polymers. Certain properties,
such as permeability and hydrophobicity, can be enhanced without
increasing the cost of the coating
significantly, and without changing
the desired benefits of the organic
products. Siloxanes have been
blended with acrylics—for instance,
in paint and render (stucco) formulations—to add desired “
breathabil-ity,” but retain the original color
and adhesion characteristics.
Whether a blend or a pure
silicone-based formulation, these
coatings and sealants are high-performance materials and certain
requirements must be met in order
to maximize the value they offer.
“Proper preparation of the substrate
and application of the product is
absolutely imperative, and it really
is best to find a contractor with
knowledge of silicone coatings
and experience in applying them,”
stresses Kimberlain.
In addition, it is important to
understand that these coatings are
not structurally reinforcing. If there
are cracks or other fundamental
problems with
the structure of a
building, monument, or bridge,
application of a
silicone-based
coating will not
correct the problem, only hide it
for a little while. For water-repellant
coatings or treatments, proper flashing and building design elements
to prevent water damage from occurring must also be implemented
prior to application.
“Any structural damage must be
repaired and proper water management systems should be in place before silicone coatings and sealants
are applied,” asserts Selley. “Once
these issues have been addressed,
silicone sealants and coatings can
be applied and begin protecting important architectural features.”
They have been used widely
throughout North America and
around the globe to do just that.
Many lighthouses have been protected with silicone coatings. These
structures are exposed to very harsh
conditions—salt water atmosphere
and extreme temperatures.
Dow Corning’s AllGuard
Silicone Elastomeric coating has
been applied to a lighthouse in
Newfoundland, Canada, for example, to prevent any further deterioration. AllGuard prevents liquid water from penetrating while allowing
water vapor to escape, making it an
ideal coating for this situation. The
product has undergone tests that
demonstrate it can withstand 24-
hour exposure to 98-mph winds, to
simulate wind-driven rain, without
experiencing any weight gain for the
underlying cementitious substrate.
In the United States, Mount
Rushmore, Washington National
Cathedral, and Statue of Liberty
have been preserved using Dow
Corning sealants. The National Park
Service uses silicone sealants to
fill cracks in the Mount Rushmore
monument. Dow Corning 790
Silicone Building Sealant exhibits
natural adhesions to stone and
other cementitious materials and
also is very elastic once cured.
“This ultra low modulus sealant
is very flexible and thus does not
exert significant stress on the fragile
substrate of the monument and
helps prevent any further damage,”
remarks Kimberlain. It also provides
watertight bonds to granite joints,
and can be applied over a wide
range of temperatures.
The Washington National
Cathedral, the sixth-largest cathedral in the world and second-largest
in the United States, is a solid
masonry structure built from high-grade limestone blocks that average
300 pounds. Although just completed in 1990, the Cathedral took
over 80 years to build, and many
of the initially constructed sections
already require restoration. As part
of ongoing renovation/preservation
efforts, deteriorating mortar is being
replaced with silicone sealants.
The Statue of Liberty required
repair of a very thin copper façade
that deteriorated due to exposure
to wind-driven salt water for 100
years. The monument suffered significant rust and corrosion and also
instability of its underlying substrate. Silicon-based sealants were
chosen for the restoration project
because of their neutral curing system, according to Kimberlain. They
also provide superior adhesion capabilities to copper, flexibility in extreme weather conditions, long life,
and compatibility with residual coal
tar—the original sealant used when
the statue was erected in 1886.
