C. The primer dry-to-tape time is dependent on temperature and humidity and is given in Fig. 701 as a guide only. This time may be shortened or lengthened as need be, providing the tape after removal has had no visible effects on the primer film.
D. If over-spray or other surface roughness of the primer film is apparent, lightly hand-sand the dry primer with 400 or finer grit abrasive paper or Scotchbrite pads. Use extreme care to prevent removal of the primer to substrate. If this occurs, repair per par. 9.
E. Primer films that are soiled from dust, dirt and /or paint over-spray, or that have been sanded shall be carefully cleaned immediately prior to over-coating by wiping with a tack rag.
7. Enamel Mixing
A. Enamel consists of a two-component kit containing resin base and catalyst. Thinner is supplied separately.
B. Agitate the enamel base material thoroughly just prior to mixing. Agitate sufficiently to
incorporate all solids that may have settled out during storage.
C. Catalyze the enamel by adding the proper amount of catalyst to resin base according to Fig.
702. Stir the base continuously while adding the curing agent. Immediately after catalyzing, thin the enamel with the proper amount of reducer required for spray application (Fig. 702).
NOTE: Failure to thin Sterling enamel immediately may result in a shorter pot life.
D. Label container with date and hour of mixing and date and hour the pot life expires.
8. Enamel Application
A. General
(1)
Where enamel colors are applied over white the total enamel thickness is not to exceed
4.8 mils (0.0048 inch).
(2)
The dry-to-tape time at 90°F is approximately 4 hours. This drying time is dependent on temperature and humidity and is given here as a guide only. The time may be varied providing the tape after removal has had no visible effects on the enamel film. The exact time can best be determined on practice panels under shop conditions identical to those under which the airplane is painted.
(3)
Cure 8 hours minimum before exposing the paint to rain or outdoor temperatures below 70 °F.
CAUTION: PAINT DOES NOT DEVELOP MAXIMUM REISTANCE TO HYDRAULIC FLUID FOR APPROXIMATELY 7 DAYS AT 70°F OR ABOVE.
(4)
Cure paint used for touchup on fasteners, rivet heads, scratches, etc (not to exceed 36 square inches) for a minimum of 8 hours at temperatures above 70°F.
B. The recommended procedure for application of enamel is to apply two to three coats with 15 to 20 minutes dry time between coats.
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51-21-171 Page 710 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Nov 15/77
9. Metallic Enamel
A. General
(1) This paragraph describes surface preparation, mixing, application, and cure of the decorative metallic paint system. This system consists of an exterior metallic color coat plus an exterior clear overcoat.
NOTE: The application instructions for the clear overcoat apply for its use over all colors.
(a)
Apply the total BMS 10-72 system specified on the drawing.
NOTE: Enamel barrier coat is not required for use on fiberglass nor under aluminum pigmented metallic paints.
(b)
Mask as required to isolate the area to be overcoated with metallic paint.
(c)
Apply BMS 10-72 metallic enamel according to par. 8.C.
B. Metallic Enamel Mixing
(1)
The exterior metallic color coat consists of a three-component kit containing component A, clear resin base, component B, catalyst and component C, metallic powder, component D, thinner is supplied separately.
(2)
Mix the materials in clean containers without organic liners.
(3)
Add approximately 1/3 by volume of component A, resin base, to component C, powder, and stir into a smooth paste. Mix thoroughly. Add the remainder of the resin base, while stirring. Slowly add the catalyst to the powder-resin mixture while stirring. Shake for 3 to 5 minutes, then let stand for 5 minutes without agitation. Label the container with the time of mixing and time the pot life expires (4 hours for aluminum powder pigmented systems and 1 hour for gold powder pigmented systems). Do not use material whose pot life has expired.
(4)
Hand-stir for 3 to 5 minutes and strain through cheesecloth or an equivalent strainer. Just prior to application, thin as required for spray consistency with component D thinner.
(5)
Mix clear enamel overcoat according to enamel mixing instructions of par. 6 and Fig. 702.
(6)
Clean spray gun equipment with toluene.
C. Metallic Enamel Application
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