TM 5-805-6
ants based on the same type of polymer; the
high-solids content of these sealants minimizes
primary difference is the curing time.
shrinkage during the curing process.
(1) A catalytic curing reaction uses a catalyst
10. Selection of Sealants. The applications listed
or "activator" which triggers the polymerization of
below range from the least demanding interior
the sealant. Small quantities of catalyst will pro-
caulking to the most demanding exterior struc-
mote the reaction which may be accelerated when
tural sealants. Table 1 provides a general compari-
very little additional catalyst is added to the mix.
son of sealants.
(2) Co-polymerization results when two or
a. Interior joints in wood, masonry, concrete, and
more different polymers react to produce a third
metal. Joints with short life, no movement, and no
exposure to standing water can be filled with
polymer (or co-polymer) system.
inexpensive oil-and-resin-based caulking. Paint
(3) Mixing is done just before or during the
will extend the service life by protecting the
application so that the "pot life" is long enough to
caulking from occasional water exposure, retard-
allow the sealant to be placed in the joints. The
ing loss of volatile constituents, and filling small
mix ratio is tailored to allow control of the cure
cracks in the caulking.
time, sometimes progressing to an early-strength
tack-free stage in as little as 1 hour.
formed sealants are used to fill interior joints that
(4) Mix-proportions must be closely controlled,
will not move and where the soft sealant will not
mixing must be thorough, and the mixed sealant
be disturbed (usually hidden from view).
must be used before expiration of its pot life and
c. Exterior joints protected from standing water
shelf life. These sealants may be mixed with
or severe weather. Acrylic sealants are suitable
special equipment as they are applied or pre-mixed
where joint movements do not exceed 15 percent,
and loaded into sealant gun cartridges. The car-
and water exposure is limited. Quality varies;
increased acrylic content improves performance
tridges are sometimes frozen to extend the pot life
and increases cost. The solvent-based acrylics are
of the material. Curing is always accelerated by
generally superior to those with a water base.
increased temperature and sometimes by increased
Paint will help protect acrylic sealants. Elastome-
humidity.
ric and structural silicone sealants are also suit-
(5) The properties of two-component sealants
are generally similar to the one-component seal-
able for these applications.
Table 1. General Guide to Sealant Selection
*
Cure
Total Joint
Sealant/
Movement
Design Life/Comments
Primary Use
Substrates
Time
Shrink
15%
5 to 20 yrs. Paint will help pro-
Slow
Acrylic latex
Porous
Yes
tect. No standing water.
Interior,
Non-moving joints.
Polysulfide
25%
5 to 20 yrs.
Single
All
Yes
Slow
5 to 20 yrs.
50%
Multi-
All
No
Variable
All joints except traffic.
Resists traffic abuse.
Polyurethane
5 to 20 yrs.
50%
Single
All
Slow
No
50%
5 to 20 yrs.
No
Multi-
All
Variable
All joints.
Will not accept paint.)
Silicone
(Resists high & low temperatures.
50%
10 to 20 yrs.
Single
All
Slow
No
10 to 20 yrs.
50%
All
Multi-
Variable
No
All joints except traffic.
Will not accept paint.
Structural Silicone
20 yrs.
50%
All
Slow
No
Single
50%
20 yrs.
Multi-
All
Variable
No
Used to support smooth-faced
exterior glass & panels.
11
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