TM 5-805-6
the first fuel resistant sealants. The loss of water
Special "siliconized acrylic" sealants will adhere
when curing causes these sealants to shrink, and
to metals and glass. The comparatively inexpen-
their physical properties have been surpassed by
sive vinyl acetate-acrylic copolymer sealants have
those of the silicones and polyurethanes.
poor resistance to water and ultraviolet and they
(b) Two-component polysulfide sealants were
are limited to near-zero joint movement.
first developed for sealing integral tanks in air-
(3) Uncured acrylic latex sealants clean up
craft in the early 1950's. They provide high solids
readily with water. During the relatively slow
content (thus little or no shrinkage) and good
curing time, acrylic sealants are susceptible to dirt
adhesion to most construction materials. Early
pickup. Acrylic sealants resist attack by ultravio-
applications werre limited because of the high cost
let, salt spray, and weathering. They are vulnera-
of the polymer, but their good performance in a
ble to attack by esters, ketones, aromatic hydrocar-
few high quality architectural applications re-
bons, petroleum products, and oxidizing chemicals.
sulted in a larger market and reduced costs.
Acrylic sealants are generally limited to a total
Two-component polysulfides are widely used in
joint movement of plus or minus 12.5 percent,
building construction. The cure rate can be ad-
although silicone-acrylics can resist joint move-
justed to provide adequate pot life and short cure
ment as high as 50 percent.
time.
(4) Acrylics are available "clear" and in colors,
(2) Polyurethane sealants. Tough, flexible pol-
and they may be painted, although joint move-
yurethane sealants are often used on sidewalks
ment may crack the paint.
and industrial floors. Clear polyurethanes have
g. Elastomeric sealants. An elastomeric sealant
poor resistance to ultra violet light, but pigments
is one which will withstand a joint movement of at
provide considerable protection. Polyurethanes are
least 25 percent (plus or minus 12.5 percent).
available in colors and can be painted. Polyure-
Elastomeric sealants are classified as single- or
thane is also used with several co-polymers; an
multi-(usually two-) component; pourable or non-
epoxy co-polymer, for example, will enhance hard-
sag; allowable joint movement (plus or minus 25 or
ness and water resistance. The service tempera-
12.5 percent); for use in traffic or no traffic; and
ture range for polyurethane sealants is from -40
for use on mortar, glass, aluminum, or "other"
to 83 degrees C (-40 to + 180 degrees F). Life
substrate. Paint should be applied to elastomeric
expectancy of a quality urethane sealant may be
sealants only when the joint has little or no
as high as 20 years.
movement; otherwise, when the sealant elongates,
(a) Polyurethane sealants can withstand
the paint surface will crack. Most of the elastome-
joint movement of 50 percent (plus or minus 25
ric sealants will provide good service in severe
percent).
weather exposures and can be used in place of oil-
(b) Specially compounded polyurethane seal-
and resin-based caulking or acrylic sealants.
ants may be used in areas exposed to liquid
Elastomeric sealants may lack sufficient strength
oxygen (LOX). Many polyurethane sealants have
or durability for use as structural (load-bearing)
good resistance to petroleum products; however,
sealants. Performance characteristics vary, de-
manufacturer's data should be consulted for spe-
pending on the type and amount of polymer and
cific exposures.
other ingredients.
(c) Unopened containers of single-component
(1) Polysulfide sealants. Polysulfides react
polyurethanes have a relatively short shelf life of
with strong oxidizers and may ignite in presence
6 months to a year. An open container of polyure-
of liquid oxygen or concentrated hydrogen perox-
thane sealant will soon increase in viscosity until
ide. Polysulfide sealants can be used in joints that
it is no longer usable.
move as much as 50 percent (plus or minus 25
(d) Increased temperature and humidity
percent). Polysulfide sealants are available in col-
will shorten the pot life. Polyurethane foam seal-
ors and will accept paint. The service temperature
ant and foam insulation are produced by adding a
range for polysulfide sealants is from -30 to + 65
blowing agent, e.g., an aerosol in a can or two
degrees C (-20 to 150 degrees F), except for
parts mixed in a spray. The resulting foam must
aircraft sealants which are specially compounded
be protected from ultra violet exposure.
to permit operation at -40 degrees (C or F).
(3) Silicone sealants. Silicone sealants have
Polysulfide sealants hold up well when fully im-
excellent weather resistance and a service temper-
mersed, as in swimming pools. At one time, poly-
ature range from -54 to + 204 degrees C ( -65 to
sulfide sealants dominated the market for high
+ 400 degrees F). Good quality silicones are supe-
performance sealants for buildings.
rior to most other types of sealants with regard to
(a) Polysulfide single-component sealants
flexibility, elongation, capacity to absorb joint
are usually latex dispersions which were among
7
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