for 1 hour. The total dry film thickness of primer
should be 0.6 to 0.9 mil. If the temperature is below
70°F, you should allow 2 to 3 hours for drying. Do
not spray if the temperature is below 50°F.
Polyurethane Paint Systems
All personnel assigned duties involving the
mixing and application of polyurethane coatings
should receive a preplacement and periodic medical
evaluation. The date and results of each medical
evaluation should be entered on the Administrative
Remarks page of the individuals service record and
in the individuals training jacket.
The polyurethane systems used on naval aircraft
consist of two types. The aliphatic type is used in
MIL-C-83286 polyurethane paints. The aromatic
type is used in MIL-C-85322 rain erosion-resistant
These materials generally present no
special hazard to health when they are cured (dried).
They do require special precautions during their
preparation, application, and curing because
isocyanate vapors are produced. The untreated
isocyanates released can produce significant irritation
to the skin, eyes, and respiratory tract even in very
small concentrations. They may also induce allergic
MIL-C-83286 aliphatic polyurethane is the
standard general-purpose exterior protective coating
for aircraft surfaces.
Its unique combination of
flexibility, gloss retention, and resistance to fuels and
lubricating oils make the coating extremely suitable
for aircraft exterior surfaces.
It is supplied as a
two-component kit of base and catalyst. You should
use aliphatic polyurethane over epoxy-polyamide
primer and for touchup and insignia marking over
polyurethane paint systems.
All personnel using polyurethane touchup
operations should wear protective clothing as
described in NA 01- 1A-509. Unprotected personnel
should not be permitted closer than 15 feet to the
spray zone during paint application with a brush,
roller, or spray equipment. They should be permitted
no closer than 40 feet during applications with
compressed-air spray. Unprotected personnel should
not be permitted closer than 15 feet to newly painted
surfaces for 30 minutes after the painting operation is
completed unless forced air exhaust ventilation is
Aliphatic polyurethane paint is available in kits
consisting of 1 part pigmented material and 1 part
clear resin component.
When you mix aliphatic
polyurethane paint, the clear resin component should
always be added to the pigmented component. Only
material from the same kit should be mixed together.
However, two or more kits of the same color and
manufacturer may be mixed in the same vessel. You
should not mix clear resin components and pigmented
components from different manufacturers. You
should also follow the prescribed mixing ratios to
prevent long drying times, poor chemical resistance,
or loss of flexibility. You should use a mechanical
shaker to agitate the pigmented component for at least
20 minutes. Then add the clear resin slowly to the
pigmented component while you are stirring the
pigmented component. Ensure the pigmented
component and clear resin are thoroughly mixed. You
should mix only the amount of paint that you can use
in the 4-hour pot life of the mixed paint. When
painting with polyurethane paints, you should clean
the paint gun at the end of each use or every 4 hours,
whichever comes first.
To spray aliphatic polyurethane paint, you should
thin it with MIL-T-81772 to the desired spray
viscosity. Then stir the mixture, strain it through
cheesecloth, and allow it to stand for a minimum of 15
minutes. If the viscosity of the mixed paint is too
thick for spraying within 3 hours after mixing, it may
be thinned again by adding MIL-T-81772 thinner.
You should not attempt to rethin paint after 3 hours
because it tends to produce orange peel or dry spots.
Aliphatic polyurethane paint should be applied
over a clean epoxy-polyamide primer within 8 hours
of primer application. For the best results, you should
apply the topcoat as soon as the primer is dry. You
should apply the minimum thickness required to hide
the primer. Apply two thin, wet coats about 30
minutes apart. Do not apply a mist coat because it
may cause a low gloss. A primer or topcoat that has
aged longer than 24 hours should be scuff sanded and
cleaned before it is painted. You should allow
approximately 8 hours for painted surfaces to dry.
Additional time, usually 1 or 2 hours, will be required
if the temperature is below 70°F.
During the application of an aliphatic
polyurethane topcoat, certain discrepancies may
appear on the finish because of faulty application
The most common defects, probable
causes, and preventions are listed in NA 01-1A-509.
If any of these defects are found, they should be
corrected before you continue to paint.