require three to four coats to cover the primer. A 5 to 10
After the primer has cured, apply the first coat of
minute air-drying interval should be allowed between
Du Pont Teflon filled polyurethane paint as a thin wet
coats. Apply only the minimum thickness required to
coat approximately 0.6 of an inch thick (tack coat). Do
cover the primer coat and allow 1 hour to dry.
not dry mist or flood the first coat.
Allow a minimum of 30 minutes for the solvent to
Zinc Chromate Primer TT-P-1757
flash off the first coat, and then apply a full wet coat
(1.5 to 2.0 mils). Allow an additional 30 minutes to
Zinc chromate primer is intended for use as a
cure. Repeat the application process until a topcoat dry
general-purpose interior protective coating for metal
film thickness of 5 to 6 mils is obtained. Allow the
surfaces. Depending on the location, zinc chromate
complete system to cure overnight. The full cure takes 7
primer may or may not require a topcoat. Primer is
to 10 days at 70F to 75F (21.1C to 23.9C).
relatively easy to apply and remove. Zinc chromate
primer is a single component. You should thin primer
Epoxy-Polyamide MIL-C-22750
with TT-T-548 toluene or TT-M-261 methyl ethyl
ketone. Do not use zinc chromate primer on exterior
Epoxy-polyamide is an alternate material for
aircraft surfaces, wheel wells, wing butts, or in areas
aliphatic polyurethane. The epoxy-polyamide topcoat
that are exposed to temperatures exceeding 175F
is a two-component kit. One part of the kit contains a
(79.4C).
pigmented component; the other part of the kit contains
clear resin. The pigmented component and clear
Enamel Finishes
resin are mixed in a one-to-one ratio prior to use. The
local air pollution regulations, mixing, thinning
Most enamel finishes used on aircraft surfaces are
and application instructions for MIL-C-22750
baked finishes that cannot be touched up by
epoxy-polyamide topcoat are identical to those for
organizational or intermediate levels of maintenance.
aliphatic polyurethane with the following exceptions:
Minor damage to conventional enamel finishes
The stand time after mixing is 30 minutes, and it should
ordinarily used on engine housings is repaired with
be thinned with MIL-T-81772 (preferred) or
epoxy topcoat material or air-drying enamel.
MIL-T-19544 (alternate). You should allow the thinned
paint to stand for a minimum of 30 minutes before it is
Elastomeric Rain Erosion-Resistant Coating
used. The total mixing, thinning, and stand time should
MIL-C-7439
not exceed 1 1/2 hours. The time between coats should
be about 30 minutes, and the temperature during
Elastomeric coatings are used as a coating system
application should not be less than 50F. The
to protect the exterior laminated plastic parts of
application of epoxy-polyamide is not limited by
high-speed aircraft, missiles, and helicopter rotor
relative humidity or high temperatures.
blades from rain erosion. They offer good resistance to
the effects of weather and aromatic fuels. Excellent
Acrylic Nitrocellulose Lacquer
adhesion is obtained after a 7-day-drying period.
Repairs to these coatings in the field are
MIL-L-19537
(gloss)
and
MIL-L-19538
impracticable because of the long curing time. Kits are
(camouflage) acrylic nitrocellulose lacquers are the
available to repair coatings where limited touchup is
preferred topcoat materials for aircraft markings and
required. These kits contain a primer, neoprene topcoat,
propeller safety stripes. MIL-L-19538 is also used for
and antistatic coating. If the radome or leading edge
paint touchup of avionic components and instruments.
coatings are in bad condition, they should be stripped
You may thin MIL-L-19537 or MIL-L-19538 to a
completely and recoated with epoxy primer and acrylic
spraying viscosity by thoroughly mixing 1 part of
topcoat as a temporary measure. If schedules and
lacquer with approximately 1 part of MIL-T-19544
conditions permit adequate curing of elastomeric
thinner (preferred) or MIL-T-81772 thinner (alternate).
coatings, these original coatings may be replaced.
The exact thinning ratio should be determined by the
The repair kits are normally bought open purchase
user and adjusted to the temperature, relative humidity,
to ensure that fresh materials are available. They should
and spraying equipment. Acrylic nitrocellulose lacquer
be stored in a cool place or refrigerated. Heat
that has been thinned to spraying viscosity should be
accelerates their aging. Stripping fiber glass surfaces
applied to a thickness of 1 to 2 mils. Acrylic
should be done according to the current maintenance
nitrocellulose lacquer with an aerosol container may
5-30
