MIL-HDBK-1110
in the past because they were inexpensive and easy to use. They
have good water resistance but weather poorly in sunlight. They
are used much less now because of toxicity concerns and their
limited durability.
Bituminous Coatings
Advantages
Limitations
Low cost
High in VOCs
Easy to apply/repair/topcoat
Poor solvent/heat resistance
Good water resistance
Poor weathering
Good film build
Black color only
Low level of surface preparation
2.3.4
Epoxy Coatings. Epoxy coatings are two-component
thermosetting products. (Epoxy-ester coatings are modified oil
coatings, refer to par. 2.3.1.) One part is commonly called the
base and the other, the catalyst component, although they are
both best described as coreactants. Epoxies are available in a
variety of formulations. Those most commonly used in general
service are the epoxy polyamide (which has better water
resistance) and the amine-cured epoxy (which has better chemical
resistance). Epoxies and polyurethanes provide the best overall
combinations of film properties of any organic coatings.
a) Epoxy films are tough and relatively inflexible.
Thus, they cannot expand or contract much without cracking.
However, they bond well and are very durable in most
environments. They require a blasted steel surface, and they
chalk freely in sunlight. An aliphatic polyurethane finish coat
is usually applied when the coating is exposed to sunlight.
Epoxies can be formulated to be low in VOCs, some actually
solvent-free.
b) Epoxies, as do all thermosetting coatings, have
topcoating problems. Solvent from a topcoat cannot penetrate a
fully cured epoxy to bond tightly to it. Thus, a topcoat of a
multiple coat system is applied when the undercoat is still
somewhat tacky (e.g., within 4 days). If this is not possible, a
fog coat (thin coat of about 2 mils wet film thickness) is first
applied by spray and allowed to cure to a tacky state (e.g., 4
hours) before a full coat is applied.
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