MIL-STD-186 Protective Finishing For Army Missile Weapon SystemsThis standard establishes the minimum requirements for procedures, materials, and systems for cleaning, plating, painting and finishing metals, wood, electronic materials, parts and assemblies for rockets, guided missiles, and components to protect them from deterioration.

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MIL-STD-186F (MI)

for thinning materials for spray application at other than standard room temperature and humidity conditions shall be as specified in the applicable process specifications, or shall be determined experimentally by the applicator. The application of lacquers under other than normal conditions shall be performed in accordance with best industry practices.

5.5.4.3.1 Enamel. For enamel topcoats, polyurethane paint, epoxy primer, wash primer, and epoxy topcoats, air temperatures shall be not less than 15.5°C and not greater than 37.7°C, and the relative humidity shall be not greater than 90 percent.

5.5.4.3.2 Lacquer. Air temperatures shall be not less than 15.5°C and not greater than 32.7°C, and the relative humidity shall be not greater than 85 percent except in the case where lacquer is used with blush-retardant thinner, then 90 percent is permissible, in accordance with 5.5.4.3.

5.5.4.4 Time of application of paint-type materials.

5.5.4.4.1 First coat. Surfaces shall first receive a coat of wash primer, or where other preparatory treatment has been provided previously, then the first primer coat shall be applied in not more than 2 hours after final cleaning.

5.5.4.4.2 System. Surface coatings shall be applied as follows: Preparatory coating plus primer plus first enamel or lacquer coat shall be applied on the exterior surfaces within 24 hours. Where production operations are suspended for short periods (over week-ends, holidays, etc.) this time may be extended as necessary, but shall not be greater than 72 hours, provided the adhesion is unaffected thereby, as determined by the wet tape scratch adhesion inspection test described in 6.5.4. OUTDOOR STORAGE OF PRIMED PARTS BEFORE SUBSEQUENT FINISHING OPERATIONS IS PROHIBITED.

5.5.4.4.3 Dry time (wash primer). The wash primer coat shall be allowed to dry for not less than 60 minutes (although it may dry to handle within a few minutes), but not more than 4 hours prior to application of the paint system. The primer may impair the adhesion of the paint system if prematurely applied. The wash primer shall be capable of resisting removal with the fingernail prior to application of the top coats.

5.5.4.4.4 Drying time (primer). When TT-P-1757 zinc chromate primer, MIL- P-53022/MIL-P-53030 primer, or MIL-PRF-23377 epoxy polyamide primer is used, the minimum and maximum drying times shall be those prescribed by the primer manufacturer. The minimum drying time for lacquer-type primer, under ideal atmospheric conditions, shall be not less than one hour. Under other conditions, the drying time of the lacquer-type primer shall be extended as necessary to avoid

lifting, embrittlement, and adhesion difficulties induced by the high solvency thinners