Page 565 - Handbook of Adhesives and Sealants

486 Chapter Thirteen

Polyisobutylene sealants are available as non-curing, solvent release
systems and as preformed tape systems.

13.3.2 Acrylic
Emulsions and solutions of polymethyl methacrylate or its copolymers
are used as caulking materials and sealants. They have moderate
movement capability and excellent weatherability. Acrylics tend to
have a strong odor and are usually applied outdoors.
As the solvent types gradually lose solvent, their hardness increases
and their movement capability changes from 12.5% to about 7.5%.
Recovery is poor, as the polymer is not an elastomer. The acrylic sol-
vent sealant has excellent adhesion to common construction surfaces
without primers. It is non-staining, and has excellent durability and
color performance. Resistance to weathering and UV is excellent. Only
the relatively expensive silicone sealants have better exterior dura-
bility.
Acrylic emulsions have approximately 10% movement capability.
They are water sensitive and will lose adhesion outdoors. However,
they have low shrinkage, excellent flexibility, and fair recovery. Acrylic
emulsion caulks are used indoors as bathtub caulks; for baseboard and
trim seams; and outdoors for glazing, masonry joints, and roof and
siding joints. Although most latex caulks have a movement capability
of 5–12.5%, plasticized acrylic latex sealants have 25% movement
6
and excellent adhesion to a variety of substrates. Primers are gen-
erally not necessary with acrylic sealants. They are relatively water
resistant. They have found application in the home repair market for
both indoor and outdoor projects. Acrylic emulsion sealants are con-
sidered to have better movement capability than polyvinyl acetate
sealants that are sold for the same applications. These systems clean
easily with water and can be painted over. The toxicity and odor are
not as much a concern as with the acrylic solvent release sealants. As
with most water-based sealants, one disadvantage is that the sealant
must be applied at application temperatures greater than freezing.
Acrylic sealants are subject to ASTM C 834, ‘‘Standard Specification
for Latex Sealing Compounds’’.
Two-part acrylic sealant systems are also available that contain
acrylic monomers, fillers, and initiators. They are 100% solids and
polymerize at room temperature. They have been used as polymer
concrete and for repairing potholes and cracks in concrete highways.
Although these systems are solvent free, precautions need to be taken
to avoid inhaling the strong acrylic monomer vapors.