Technical data

6.12.7.6 Thinning.
PCBTF, NSN 6850-01-399-0676, is combustible
and an irritant to eyes, skin, and respiratory tract.
Eye and skin protection required. Disposable 8
mil nitrile gloves, splash goggles, tyvek/cloth
coveralls are the recommended PPE. Use in well
ventilated areas.
NOTE
PCBTF, NSN 6850-01-399-0676 is exempt as a
VOC or HAP by the EPA and by 48 states and
will not change compliance of high solids coat-
ings to air quality regulations.
Cure accelerators are not authorized for use in polyurethane
when painting aircraft as they change the cured properties and
integrity of the coating. It can be thinned with PCBTF (NSN
6850-01-399-0676); using up to 10% by volume as a recom-
mended maximum for reduction of viscosity. The expected
viscosity as thinned will be in the range of 8 to 29 seconds in
a No. 4 Ford Cup (17 to 23 seconds in a No. 2 Zahn Cup), but
it can be up to 30 seconds in a No. 4 Ford Cup (39 seconds
in a No. 2 Zahn Cup) before thinning.
6.12.7.7 Application. MIL-PRF-85285, Type I is for
application on properly prepared and primed substrates.
Surfaces shall be prepared per Chapter 2 and primed with
MIL-PRF-23377, Type I, Class C1 or C2; TT-P-2760, Type I,
Class C1 or C2; or MIL-PRF-85582, Type I, Class C1 or C2.
Steel surfaces shall be phosphate treated or coated with
MIL-C-8514 or DOD-P-15328 wash primer and primed with
the same primers listed above. Use Type II of these primers if
low IR reflectance is required. This coating may be applied by
airless, air assisted airless, HVLP, or electrostatic equipment
after proper mixing of the base and catalyst. Apply the
coating in one wet cross-coat or two coat with the second coat
applied crosswise to the first after cure time of 4 hours. The
dry film thickness shall be 1.7 to 2.3 mils each coat per Table
5-2. Air assisted airless is preferable. For air assisted airless,
use No. 617 tip for 12 inch fan and No. 517 tip for 10 inch
fan. Atomize at eight to ten PSI at the tip with the trigger
pulled to conform to the HVLP requirement of the NESHAP.
6.12.7.7.1 APC Application. Follow application proce-
dures of Paragraph 6.12.7.5. In addition, maintain a wet edge
during each application. After the first coat, the coating
should be air dried 15-60 minutes at 75° F/ 24° C ±5° F/15°
C before application of the second coat. It is normal for
occurrences of mottling or “tiger striping”. This condition
typically disappears after coating has reached full cure.
Although the visible gloss of camouflage APC will appear to
be greater than conventional MIL-PRF-85285, APC still
meets the requirements of the military specification.
6.12.7.7.2 Maintenance Painting. Maintenance paint-
ing (touch-up) of APC shall be accomplished using same
procedures as for conventional polyurethane coatings listed in
Chapter 5. Although APC and conventional MIL-PRF-85285
coating are compatible, it is recommended to use the same
material as the previously applied coating system for main-
tenance painting. If both materials are used, a significant
color mismatch will develop as the two coatings age due to
APC’s superior color retention.
6.12.8 Curing of Complete Polyurethane System.
The cure schedule for polyurethane coatings shall be fol-
lowed. Aircraft shall not be operated until 72 hours has
elapsed at a temperature of 75° F or higher, after the topcoat
application is completed. If the temperature is less than 75° F
at anytime during the cure cycle, it is preferable to wait a full
seven days before flying the aircraft.
a. Cure time before handling, taping, masking etc., is 6
hours minimum. Time may be reduced to 4 hours if
temperature and humidity reach upper limit (90° F and
80% RH). Low temperature and low humidity (60° F
and 30% RH) retards cure rate to 12 hours minimum.
b. Curing time before movement from controlled hangar
environment at a temperature of 75° F or higher is 6
hours minimum after application of last paint coat.
Aircraft may then be moved to another location with a
controlled environment of 75° F or higher to continue its
72-hour cure.
c. Curing time before decal application, 8 hours minimum.
d. Curing time before engine run up, 30 hours minimum.
e. Curing time before wet tape test, 48 hours minimum.
f. Curing time before flight, 72 hours minimum.
g. Curing time for maintenance painting of polyurethane
system at 75° and 50% RH and higher: (Lower tempera-
tures and relative humidity require longer cure times.)
(1) Complete leading edges (All), complete control sur-
face (All), major skin panels 9 square feet and over,
and engine intake, 72 hours minimum.
(2) Skin panels less than 9 square feet, fasteners, rivet
heads, screw heads, and minor chipped and scratched
areas, less than 36 square inches, 30 hours minimum.
6.12.9 Coating Compound (Wash Primer), Metal Pre-
treatment, Resin-Acid, Specification MIL-C-8514.
6.12.9.1 Characteristics. The term “wash primer” des-
ignates a specific material which combines the properties of
TO 1-1-8
Change 3 6-13