A variety of sealant materials have been used over the years, and very good materials are available
today for a variety of applications including exposed expansion and control joints, joints between
cladding panels, the perimeters of wall and roof openings such as windows and doors, and
corrugated metal walls and roofs. Depending on the application and conditions to which the sealant
will be exposed, there are a variety of performance criteria that must be considered. These include
stability in storage and in the application pot, mixing, curing time, modulus of elasticity, elongation,
recovery, hardness, temperature limits of application and performance, color and color retention,
resistance to chemicals, ozone and ultraviolet radiation, bond durability and applicability. ASTM C
920, Standard Specification for Elastomeric Sealants, provides classifications for the various
properties of elastomeric joint sealants and identifies the relevant ASTM test methods. In addition
to these performance criteria, sealants should be selected based on their offgassing properties as
they affect indoor air quality. Research is currently in progress on the emission characteristics of
sealants and their impact on the indoor environment, and these results will make it easier to
consider indoor air quality in the specification of sealants.
Sealant materials can be classified by a variety of characteristics including their application, i.e.,
pourable, gun-applied, tapes and cured gaskets. Sealants may also be classified as non-hardening
or hardening, and rigid or nonrigid. Some advantages and disadvantages of different sealant
materials are presented below. This information is based on material in Panek and Cook and is not
intended to be exhaustive. More thorough discussions of specific sealants are found in Panek and
Cook and in ASTM STPs 606 and 1069.
Polysulfide sealants were the first elastomeric sealants used in modern curtain walls, starting in the
early 1950s. They have movement capabilities as high as 25%. Following the introduction of
urethanes and silicones, with their better ozone and ultraviolet resistance, the use of polysulfides
declined. They still constitute a major part of the insulating glass market, but are otherwise used
only in limited applications due to their poor recovery compared with urethanes and silicones.
Silicone sealants have very high recovery, are unaffected by ultraviolet radiation and ozone, and
have movement capabilities from 25% to 50%. Because of their high recovery, they are used in
structural and stopless glazing systems. Other advantages include excellent workability and color
stability, durabilities of over 20 years, and the fact that they are one-component sealants.
Disadvantages include cost, dirt pick-up, odor, short tooling time and some problems with obtaining
primer-less adhesion to aluminum, wood and concrete surfaces.