Technical data

e. Begin overcoating within 48 hours after scuff sanding
and conversion coating operations and immediately
after solvent wipe down. Apply one thin/mist coat of
MIL-PRF-23377 Type I, Class C1 or C2 (one full wet
coat per Table 5-2, to large bare metal areas) to the entire
aircraft or equipment exterior painted surface per in-
structions in Paragraph 5.6. Allow 5 hours at 75° F for
the primer to dry, but no more than 8 hours, and apply
2 coats of the required topcoat MIL-PRF-85285 and
appropriate paint scheme per Chapter 8 of this manual,
aircraft drawings, -23 manual, or equipment manual. If
more than 8 hours elapse (not to exceed 24 hours)
between priming and topcoat, the primer must be
solvent wiped for reactivation per Paragraph 3.1.6 or
scuff sanded with 320 or 400 grit sandpaper per Para-
graph 3.1.3 to reactivate the primer for adhesion of the
topcoat. If the primer is scuff sanded, solvent wipe per
Paragraph 3.1.4 must be reaccomplished prior to topcoat
application. If 24 hours elapses between priming and
topcoating, solvent wipe for reactivation is not permit-
ted and scuff sanding is mandatory.
f. A non-chromated tiecoat/Primer (Class N) may be used
for overcoating of existing coating systems after scuff
sanding. This is an alternative to MIL-PRF-23377 Type
I, Class C1 or C2. All bare metal areas must have primer
applied using MIL-PRF-23377 Type I Class C1 or C2
before application of the tiecoat. Allow 2 hours for the
primer to dry, but not more than 8 hours prior to
application of the tiecoat. Apply the tiecoat and topcoat
per Paragraph 5.6.2 for MIL-PRF-23377 Type I, Class
C1 or C2 and MIL-PRF-85285.
NOTE
These primers do not provide adequate corrosion
protection and shall not be applied over bare
metal areas.
5.6.3 Curing of Finishes. After painting, allow aircraft
finish system to cure in a dust-free temperature controlled
atmosphere for a sufficient time prior to placing in service. In
the absence of accelerated curing, the aircraft shall not be
flown for at least 72 hours after painting. In general, all
painted aircraft should be handled, taxied, etc., as little as
possible during the first week after painting.
5.6.4 Coating Thickness Measurements. Wet and dry
film gauges are available as local purchase items from various
laboratory supply houses. If paint film thickness measuring
instruments are not available, small (2 x 6 inches) anodized
aluminum panels will be used for measurement of the paint
thickness after drying. Apply these panels to each side of the
fuselage with a section of one inch wide masking tape
doubled back on itself with adhesive contacting the panel and
the aircraft surface prior to the painting operation. Mask one
end of the panel with tape for a distance of approximately 2
inches to provide a comparison of the original panel thickness
and the thickness after painting. Remove the panel after
application of the primer so that immediate maintenance
painting can be used to cover those areas previously protected
by the panel. This procedure will also permit locating other
panels on various portions of the same aircraft to provide a
good indication of the overall paint thickness. The location of
panels depends upon inspection procedures and may vary
throughout the aircraft. Each aircraft should use a set of
panels for each different operation employed on the aircraft
identified by the name of the painter, aircraft model, and the
date of painting, to provide follow-on data during any
subsequent service evaluation. Slight errors in paint thickness
measurements can be expected when using this method due to
thickness tolerances for the basic aluminum sheet. Measure
the paint thickness with an ordinary micrometer possessing
flat contact surfaces. Micrometers with pointed or rounded
contact surfaces are not recommended. At least 6 readings
shall be taken on both painted and unpainted portions of each
panel to provide an average paint thickness measurement.
When using a wet film gauge or an Electronic Dry Film
Gauge, a minimum of 6 readings shall also be taken. Take
readings in a 1 square foot area that is representative of the
entire area bring painted. Rejection is only if the average of
the 6 readings falls outside of the thickness range for that
particular paint system.
5.6.5 Allowable Coating Thickness. Because of the
greatly reduced corrosion protection for a dried film thickness
of less than 0.3 mils (0.0003 inch), solitary primer films
below this thickness shall be avoided. Attaining proper
coating thickness by spraying is a matter of technique plus
checking. There is a limit to the thickness that can be applied
in one pass because of protracted drying time or possible
sagging of the film. This must be considered in obtaining the
total desired thickness. Also, there is a tendency with coating
materials of good hiding power to increase the spreading rate
as the work progresses and this must be curbed. Operator
fatigue may alter the speed of working, but this should not be
allowed to result in applying more or less material to the
surface. Changing atmospheric conditions during operations
may have to be compensated for in order to continue applying
a uniform film. Frequent checks with a wet film thickness
gauge shall be made during painting to ascertain and control
film thickness. Thickness cannot be gaged accurately without
instruments, but lacking these, the best assurance of consis-
tent films is in correct adjustment of the gun for the material
being applied and the use of good judgement. See Table 5-2
for dry film thickness ranges of various primers and topcoats.
TO 1-1-8
5-10 Change 3