MIL-STD-186F (MI)
of corrosion must be abraded from the substrate. The surface immediately surrounding exposed substrate should then be sanded, using a feathering-in technique. That is, sand away paint film (primer and topcoat) so that the thickness of the film is smoothly tapered from bare metal/substrate to the top of the paint film. Sanding of any type is followed by wiping down the exposed area to be painted using a clean rag wet with MIL-T-81772 thinner to remove all loose sanding debris, mill scale, grease, oil (including fingerprints), and diesel/gasoline residue. Do not use other petroleum or alcohol-based thinners or cleaning agents of any kind. All
areas sanded down to bare metal shall be treated (sponged or damp wiped) with the appropriate solution of Appendix I or wash pretreatment on steel, or wash pretreatment or MIL-C-5541 on aluminum, allowed to react for 15 minutes. The minimum area allowed for touch-up shall be agreed upon for each contract between the Government and the applicator.
4.25.2 Finishing procedures.
4.25.2.1 Epoxy primer. Choose the appropriate primer and prepare in accordance with manufacturer directions. Apply evenly in one coat over the pretreated substrate and apply over portions of the exposed original primer coat using blend-in technique; i.e., tapering off quantity applied to a thin edge. Do not apply epoxy primer beyond the blend-in edge.
4.25.2.2 Application methods. Rework (application of CARC topcoats to sound existing topcoat) shall use the conventional techniques of spraying or brushing. For touchup, suggested procedures include brushing (see appropriate application section of primer and topcoat descriptions) or sponging/wiping (suggested for small areas requiring wash primer). Spray application by conventional techniques can be difficult, but a small, self-pressurized spray kit is available for touchup.
4.25.2.3 Film thickness. The total thickness of previous coatings shall be checked prior to reworking. Limitations on maximum film thickness to be topcoated shall be determined by an adhesion test on the existing coating. It is recommended that a total of 20 mils not be exceeded. For aircraft, the coating thickness (existing plus rework) shall not exceed 8 mils. The film thickness shall be not greater than 9 mils on a porous, cast item. If thicker prior coatings are experienced, adhesion failure and coating fissuring may result. Cracking (fissuring) of the topcoat due to too thick a film can be subtle and difficult to find (magnification is often necessary) but is cause for rejection due to chemical agent permeability.
4.25.3 Safety. For general health and safety guidance, see MIL-C-53072, Appendix B.
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