SURFACE PREPARATION
The effectiveness of any paint finish and its bond
to the surface depends upon the careful preparation of
the damaged surface before touch-up. The touch-up
paint should overlap onto the existing good paint
finish. The touch-up materials will not bond to glossy
finishes, so the finishes must be prepared. Also, any
edges of the existing film will show through the
overlap unless they are smoothed out.
To break the gloss of existing finishes and to
feather (smooth out) the edges for overlap, you should
scuff sand by using 240 or 320 grit aluminum oxide
cloth. After sanding, use a water rinse to remove the
abrasive residues.
You should remove any loosened seam sealants in
the area to be touched up and replace them as
necessary. Also, resecure any loose rubber seals by
using the type of adhesive specified in the applicable
MIM.
Then outline the area to be painted with tape and
masking paper, as shown in figure 4-32. This protects
the adjoining surfaces from overspraying and
unwanted paint buildup.
TOUCH-UP PROCEDURES
A standardized paint system for O- and I-level
painting and paint touch-up is presented in NAVAIR
01-1A-509.
Standardized exterior paint touch-up systems for
organizational and intermediate levels of maintenance
consist of an epoxy primer (MIL-P-23377, type I or
type II, as applicable) overcoated with aliphatic
polyurethane (MIL-C-85285). Paint systems are
identified by a decal or stencil located on the right side
of the aft fuselage.
Standardized interior paint touch-up systems for
O- and I-level maintenance consist of zinc chromate
primer (TT-P-1757). 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, test them by using a small sample of scrap
aluminum.
The following paragraphs furnish the basic
information for identifying and applying the standard
touch-up paint systems. Complete information on the
types and applications of aircraft paint systems is
contained in NAVAIR 01-1A-509.
Figure 4-32.—Masking before paint touch-up.
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 and separately before they are mixed
together. One part contains the pigment particles in an
epoxy vehicle. The other part is composed of a clear
polyamide solution that functions as a hardener for the
epoxy solution. This primer is supplied by various
manufacturers. You should mix only as much primer
as needed. The storage life of the primer is limited after
it is mixed to the amount that can be used in 4 hours.
Refer to NAVAIR 01-1A-509 for specifics on mixing
these two components.
Zinc Chromate Primer
Zinc chromate primer (TT-P-1757) is a
general-purpose, interior, protective coating for metal
surfaces. Depending upon the location, zinc chromate
primer may or may not require a topcoat. Zinc
chromate primer is easy to apply or remove as it is a
single component. There is no thinning required for
brush or roller application however, for spray
application, thin this primer with MIL-T-81772. Do
not use zinc chromate primer on exterior aircraft
surfaces, including wheel wells and wing butts, and in
areas that are exposed to temperatures exceeding
175°F (79.4°C).
Polyurethane Finish Systems
You must have a physical examination before you
can work with polyurethane coatings. Also, you must
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