should be taken that all of the pigment matter has been
included in the mixture.
component polyurethane paint, when applying by
conventional air atomized or airless spray, are to mix
four parts of Component A, which is the polyester
portion, to one part of Component B, which is the
components are mixed, the total mixture is left to stand
for at least 30 minutes to deaerate. The mixture (batch)
is then thinned to the proper viscosity depending upon
the spray equipment. The mix at the specified ratio will
produce a pot life of eight hours. Therefore, no more
paint should be mixed than can be used in an eight hour
shift or period.
MIL-C-46168 paint must be thinned to
spraying viscosity, determined by the user and the type
of spraying equipment to be used. A suggested starting
point is obtained by mixing approximately four volumes
of mixed MIL-C-46168 paint and one volume of MIL-
T81772 thinner. The paint must be thoroughly mixed
with the thinner and continuously agitated during
Where quantities permit, and to eliminate
the 30 minute deaeration time and potential waste,
plural component spray units can be used which
components directly at the spray gun nozzle. Since the
two components are kept separate, the pot life
consideration is also eliminated.
The polyurethane paint can also be
applied by conventional, airless, or electrostatic spray
equipment. In cases where this type of equipment is
used, the viscosity can change. The applicator should
check with the paint company and equipment supplier
for the exact criteria for viscosity, thinning and the best
Whatever spray equipment is used, it is
necessary that all spray guns, lines and nozzles, when
applicable, be thoroughly cleaned after use to prevent
hardening of the coating system. If the coating hardens
in the system, the system cannot be cleaned. That
portion of the unit in which the paint has gelled or
hardened must be discarded.
MIL-C-46168 paint may be applied over a
wide range of temperatures. Temperatures from 50 to
90°F (10 to 32°C) are recommended for best results.
MIL-C-46168 paint is a catalytic paint and
conditions after application. However, at
very low temperature, curing is retarded.
Test the mixture, pressure, and spray
equipment settings by applying a test coating to
masking paper or similar smooth surfaces prior to
application to aircraft or components. Adjust paint
and/or equipment until proper test coating is achieved.
Paint and equipment are then ready for application to
the equipment or components.
Procedures for application of MIL-C-46168 paint
to bare metal substrates. The total paint system for the
polyurethane coating, as with all other paint systems,
anticorrosive primer, and the polyurethane topcoat.
This applies to painting of bare metal substrates.
Cleaning. The substrate should be
thoroughly cleaned of all oil, grease and other
contaminants by appropriate methods cited elsewhere
herein or as specified in TT-C-490.
documents, e.g., MIL-STD-193, MIL-STD-186, MIL-T-
704, etc., provide appropriate directions for surface
preparation. For steel substrates, the pretreatments to
use are zinc phosphate per TT-C-490 Type I or wash
primer conforming to DOD-P-1 5328. For aluminum
substrates, the pretreatment is alodine, MIL-C-5541.
anticorrosive primers to be used with the MIL-C-46168
paint system are of the epoxy type. The epoxy primer
to use with steel substrates is MIL-P-52192 and for
aluminum and magnesium substrates is MIL-P-23377,
or MIL-P-85582. MIL-P-53022 may be used on
pretreated ferrous substrates if the use of lead or
chromates is restricted.
Topcoat. MIL-C-46168 coating is
applied at 1.8 to 3.0 mils dry film thickness in two coats.
The first coat should be applied within one to four hours
of the application of the primer. The second coat may
be applied within a few minutes of the first coat or
anytime thereafter. The total thickness of the topcoat
should not exceed 3.0 mils. There is no maximum time
between the application of the first and second coats,
ideally within two hours. No surface preparation, except
for cleaning, will be necessary as long as the surface