MIL-STD-171 Finishing Of Metal And Wood SurfacesThis standard establishes and updates general finish codes and serves as a general guide to the selection of suitable materials, procedures, and system for cleaning, plating, painting and otherwise finishing of metal and wood surfaces.

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MIL-STD-171F

5.2 0rganic finishes.

5.2.1 General painting guidelines. Painting shall be done in clean, dry, well-ventilated spaces. It is preferred that the air temperature be between 60 and 900F (16 and 320C) and the relative humidity not over 65 percent. Painting should not be done when the temperature is

below 500F (100C) or when the humidity is above 85 percent. Materials shall be thoroughly

mixed and there shall be no settling or separation of ingredients during painting.

Unless specifically directed otherwise, coatings may be applied by any method that will ensure the application of a smooth, uniform, continuous film, free from dried overspray, runs, sags, blisters, orange peel, or other imperfections.

Unless otherwise specified, for bake type coatings, ample flash off time should be allowed before exposing the coats of paint to a temperature of 2000F (930C) for 45 minutes. Freshly painted material shall not be exposed to conditions that will harm the paint. Pretreatment

coating MIL-C-8514 (finish 5.2) shall be applied either in accordance with that specification or in accordance with MIL-C-8507. Prior to painting magnesium alloy, first apply one of the finishes

8.1 through 8.6 or 8.9. A surface sealing coating can then be applied. AMS-M-3171 cites a surface coating resin, baking type epoxy sealer.

When pretreatment coating MIL-C-8514 (finish 5.2) is applied to magnesium alloy, its phosphoric acid content shall be reduced to 50 percent of that specified in MIL-C-8514. Additional data on the application of finishes can be found in MIL-STD-186 and MIL-F-18264.

5.2.1.1 Previously painted surfaces. Prior to the application of paint to equipment previously painted, the surfaces shall be thoroughly cleaned. If solvent is used it shall be oil free. All loose paint shall be removed. When touching up damaged areas or applying a CARC topcoat to an existing CARC topcoat, the procedure to be followed depends upon the type and condition of the existing finish. Items previously coated with alkyds, lacquers or vinyls must be stripped down to the epoxy primer if present, or to the substrate if not. For rework, polyurethane and epoxy topcoats can only be applied over previously painted epoxy or polyurethane topcoats. When it is necessary to remove the old paint it may be done with solvent-type paint remover, by abrasive blasting (finish 4.1) or other mechanical means. Care shall be used to remove residual remover and solvent from crevices and pockets. Finish 4.1 should be used only where contamination from the process will not harm the surface being cleaned or any adjacent parts. Regardless of the method, no harmful residues shall be left on the surface. Reapplication of the paint system shall be over a proper phosphate, chromate or wash primer pretreatment.

5.2.2 Painting schedule. The first, or priming coat of paint shall be applied as promptly as possible (preferably on the same day but, in any event, within 24 hours) after the surface has been prepared for painting. This requirement shall apply particularly to metal parts that have received a surface pretreatment.