Protecting the World’s Historical
Treasures with Silicone
ith the economy still
struggling to make a
recovery, many folks
are taking vacations
closer to home rather than
traveling across the globe. Often,
their destinations are national parks
and cities that feature historical
monuments and buildings or other
notable structures. Maintaining these
important symbols of our past so
that they can continue to educate
and astound future generations has
been a challenge.
Silicone-based coatings, sealants, and penetrating treatments,
however, have helped breathe new
life into many historically valuable structures and are becoming
recognized as important tools for
the maintenance and restoration of
buildings and monuments.
“Water is one of the most
destructive forces in nature,” states
Jon Kimberlain, an application
engineer in the technical services
department at Dow Corning
Corporation. “Siloxane polymers
are naturally hydrophobic, and
therefore afford excellent protection
against water damage.” He notes
that in the construction industry,
silicone coatings and sealants are
recognized as one of the most
durable technologies available.
These properties arise from the
nature of the siloxane, or silicon-oxygen, bond that forms the backbone of the silicone chemistry included in such products. “This bond
is very strong and resilient,” notes
David Selley, who is also an application engineer in the technical
services department at Dow Corning.
“The Si–O bond resists the destruc-
tive forces of UV energy, oxidation,
and other degradation processes.”
Silicone coatings and sealants
have a unique dual personality, according to Selley. They repel liquid
water, but are permeable to water
vapor, and thus can prevent liquid
water from penetrating a surface
while allowing any trapped water
vapor to escape, making the coatings permeable.
Being neutral curing makes silicone coatings and sealants very suitable for construction applications.
Metal and cementitious materials
like concrete account for a significant portion of the surfaces that
need to be restored and/or maintained. Formation of acidic or basic
byproducts in the curing process
can actually contribute to further
degradation of the structures that
the coating or sealant is designed
to protect. This scenario does not
occur when neutral-curing silicones
are used.
Furthermore, a broad range of
functionality can be incorporated
into the siloxane backbone through
the use of different reaction groups
on the silane monomers and polymers. Alkyl and aryl groups, fluoro-substituted organic groups, and
wholly inorganic components can
be utilized.
The result is the ability to tailor
the properties of the coating or sealant for specific applications. For
example, Dow Corning has developed a sealant, Dow Corning 795
Silcone Building Sealant, that will
adhere strongly to metal without the need for a primer, but this product is not suitable for concrete without primer. Conversely, Dow Corning 790 Building Sealant ad- heres well to porous ubstrates, like con- crete, but it typically requires the use of a primer if it is going to be applied to a metal surface. “The ability to incorporate such diverse functionality
provides great
flexibility to our product developers,” observes Selley. “As a result,
we can design products to perform
well in a wide range of specific
conditions. Such flexibility, when
combined with the durability of silicones, creates endless opportunities
for these materials in construction
applications.”
Other sealants on the market are
typically organic based. An example
is urethane-based formulations.
These sealants do perform well,
but often only last for about five to
seven years. As coatings or surface
treatments, organic-based products
may require the addition of UV stabilizers and also are true coatings
that experience wear over time.
Silicone coatings and sealants are
naturally UV resistant and are there-
fore much more durable, according
