DESIGN/SEALANTS
Urethane Sealants
Urethane sealants were developed in the early 1970s and are the most used sealants for building
joints followed by silicones, with polysulfides a distant third. They have movement capabilities of
about 25%. The advantages of urethanes include excellent recovery, long work life, negligible
shrinkage and good resistance to ozone and ultraviolet radiation. The disadvantages of urethane
sealants include poor water immersion resistance, so they are not recommended for wet joints.
One-component urethanes have limited stability and take a long time to cure.
Solvent-Based Acrylic Sealants
This general class of sealants is described as semi-elastomeric, with movement capabilities from
7.5% to 12.5%. They adhere well to many surfaces without primers, are generally one-component,
have good ultraviolet and chemical resistance, and have durabilities of over 20 years. On the
negative side, they cannot be used in joints greater than about 20 mm (3/4 inches) wide, have poor
recovery and water resistance, and are associated with strong odors.
Butyl Caulks
Butyl caulks are characterized as low cost, very stable, non- or slow curing, and are widely used as
caulks and adhesives in concealed rather than exposed locations. They are not recommended for
large movement applications, based on their maximum movement capabilities of 7.5%. Therefore,
they do not compete with polysulfides, urethanes or silicones in high movement applications.
Latex Sealants
Latex sealants are a general class of sealants employing several different materials and used for a
range of applications. Latex sealants employing acrylics as their chief materials, have movement
capabilities of 7.5% and are used outdoors. Sealants employing vinyl acrylic and polyvinyl acetate
are used indoors where the temperature gradients and movements are smaller. Latex sealants are
one-component, gun-grade materials, with fair flexibility, little recovery, and high shrinkage. They
clean up easily and are commonly used in light construction.
Oil- and Resin-Based Caulks
These materials are nonelastomeric, with movement capabilities of only 2% to 5%, and are used in
joints with little or no movement. The advantages of these low-cost, one-component caulks include
easy application and tooling, durabilities greater than 10 years, no handling or storage problems,
and no requirements for joint cleaning or priming. Their disadvantages include no recovery, little
flexibility, as much as 20% shrinkage, and low movement capabilities.
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