First, you should remove all loose seam sealants
in the area to be touched up. Replace them as
necessary. You should also secure loose rubber seals
with the type of adhesive specified in the applicable
MIM.
The area to be painted should be outlined with
tape and masking paper, as shown in figure 14-30.
This protects the adjoining surfaces from overspray
and paint buildup.
TOUCHUP PROCEDURES
A standardized paint system for organizational
and intermediate level painting and paint touchup has
been developed by the Naval Air Systems Command.
Standardized exterior paint touchup consists of an
epoxy primer (MIL-P-23377, type I or type II)
overcoated
with
aliphatic polyurethane
(MIL-C-81773 or MIL-C-83286) or alternate paint
system. Paint systems are identified by a decal or
stencil located on the right side of the aft fuselage.
Standardized interior paint touchup systems
consist of TT-P-1757 zinc chromate primer. Paint
materials that are within their original shelf life or
within an extended shelf life are preferred. However,
if materials are beyond shelf life date, you should test
them on a small sample of scrap aluminum.
Epoxy-Polyamide Primer MIL-P-23377
The epoxy-polyamide primer is supplied as a
two-part kit. Each part must be stirred or shaken
thoroughly before mixing. One component contains
the pigment in an epoxy vehicle, while the other
component consists of a clear polyamide used as a
hardener for the epoxy resin. These components are
packaged separately and have excellent storage
stability. However, when the two parts are mixed, the
pot life is limited to 8 hours. Only the amount that
you can use in 8 hours should be mixed. The
established mixing ratios must be followed closely,
otherwise poor adhesion, poor chemical resistance, or
inadequate drying may result. The clear polyamide
hardener should always be added to the pigmented
component.
CAUTION
Do not mix components from different
manufacturers.
Figure 14-30.—Masking prior to paint touchup.
The mixed epoxy-polyamide primer can be
thinned to obtain the proper viscosity for spraying.
However, you should check the local air pollution
regulations for restrictions and regulations regarding
the use of certain solvents and thinners.
To spray epoxy-polyamide primer, you should
thin it with MIL-T-81772, type II (preferred) or type I.
The thinned primer should be stirred thoroughly,
strained, and allowed to stand for a minimum of
15 minutes prior to spraying it. The thinning ratio
may vary to obtain the proper spraying viscosity,
which is 17 to 18 seconds in a No. 2 Zahn cup. The
15-minute standing time permits the components to
enter into chemical reaction, reduce cratering,
preclude the clear resin component from “sweating
out” or separating, and to allow any bubbles (formed
while stirring) to escape.
WARNING
You should wear goggles when mixing or
using thinners and solvents. You should
also wear goggles or a face shield,
respirator, rubber gloves, and coveralls
during all paint touchup and paint
spraying. Eating, drinking, or smoking
should NOT be allowed in areas where
paint or solvent is being used or stored.
Before you apply the primer, ensure that the
surface has been cleaned, chemically treated, and
prepared for spraying. Then, apply a cross coat of
epoxy-polyamide primer and allow the coat to air dry
14-32
