MIL-HDBK-1110
Epoxy Coatings
Advantages
Limitations
Low in VOCs
Limited pot life
Good solvent/water resistance
Chalk in sunlight
Tough, hard, smooth film
Cure best above 50 degrees F
Good adhesion
Topcoating is a problem
Good abrasion resistance
Blasted surface needed
2.3.5
Coal-Tar Epoxy Coatings. Coal-tar epoxy coatings are
basically epoxies (with all properties of epoxies) to which coal
tar has been incorporated. The coal tar reduces cost, improves
water resistance, and provides for greater film builds. Because
of the coal tar, coatings tend to become brittle in sunlight, and
there is great concern about toxic effects of the coal tar. They
are used primarily on steel piling and other buried structures.
The catalyst component is usually either a polyamide or an amine.
Coal-Tar Epoxy Coatings
Advantages
Limitations
Low in VOCs
Toxic; personal protection needed
Good water/chemical resistance
Limited pot life
Good film build
Blasted surface needed
Good abrasion resistance
Topcoating is a problem
Available only in black, dark
red, or aluminum
2.3.6
Polyurethane Coatings. Polyurethane coatings are one-
or two-package systems. For two-package systems, one component
is an isocyanate and the other a polyol component. Because of
the reactivity of the isocyanate, polyurethanes are moisture
sensitive, and the gloss may drop when the wet film is exposed to
high humidity. One component types cure with moisture supplied
from the atmosphere. The toxicity of the isocyanate component is
of great concern, and personal protection, including respirators,
must be used when applying them. They require skilled
applicators. Polyurethane coatings are available in a variety of
formulations, giving rise to a variety of properties (e.g., may
be tough or elastomeric). They perform well in most
environments. Aliphatic polyurethanes have excellent weathering
in sunlight; aromatic polyurethanes do not, but they have better
chemical resistance. Both types can readily be formulated to be
low in VOCs.
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