MIL-HDBK-1110
(1)
Water soluble (of limited value)
(2)
Water reducible
(3)
e) Water soluble coatings are not durable enough for
general use. The other two types of waterborne coatings find use
on military facilities, although they may be somewhat less
durable in some environments than corresponding solvent-based
types. Water-reducible coatings contain a solvent blend that can
be thinned with water. Alkyd and epoxy formulations are
available in either water-reducible or emulsion forms. Such
alkyd films are cured by air oxidation, and two-component epoxy
films by chemical reaction.
2.2.3
Chemical Reaction. Coatings that cure by chemical
reaction are usually the most durable. They are generally
packaged in two separate containers that are mixed to initiate
the reaction. Components must be combined in the specified
proportions in the manner specified by the supplier to achieve a
film with optimum properties. Sometimes, an "induction period"
is required after mixing and before application to permit the
reaction to get started. After mixing, there is always a "pot
life" during which the coating must be applied, before the
reaction has advanced so far that the coating cannot be properly
applied.
a)
Examples of coatings that cure by chemical reaction
are:
(1)
Epoxies
(2)
Coal tar epoxies
(3)
Polyurethanes
(4)
Polyesters
b) Because these coatings are thermosetting, they have
excellent chemical and solvent resistance. They are difficult to
topcoat when fully cured, because topcoat solvent cannot bite
into the films. Thus, a topcoat is best applied while the
undercoat still has some residual tack. If a completely cured
thermosetting coating is to be topcoated, it is necessary to
first spray a thin (e.g., 2 mil wet film thickness) tie coat
(tack coat) of the topcoat and allow it to cure to a tacky state.
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