Aerospace Primer and Paint Systems: Specs, Thickness and Color

Updated October 12, 2026

The system, layer by layer

Paint performance is a system property: pretreatment, primer and topcoat are qualified to work together, and most field failures trace to a skipped or mismatched layer. An HDIAC technical inquiry for DoD found MIL-DTL-5541 Class 1A conversion coating to be the pretreatment most commonly used across the services under aircraft epoxy primers, unless the part manufacturer specifies otherwise.

These are qualified products specs. MIL-PRF-23377K, for example, requires the primer to be listed in the qualified products database before contract award, so a buyer should get the product name and QPD listing on the paint cert. Pretreatment detail is on our chem film and anodizing pages.

Epoxy primers: MIL-PRF-23377 and MIL-PRF-85582

Both primers share the same type and class scheme; the difference is the carrier. MIL-PRF-23377 is solvent-borne high solids and MIL-PRF-85582 is waterborne, and both cap VOC at 340 grams per liter (2.8 pounds per gallon) as supplied.

• Type I uses standard pigments; Type II uses low infrared reflective pigments, with total reflectance of no more than 10 percent from 700 to 2,600 nanometers in MIL-PRF-23377K, and must be dark green, black or gray.
• Class C1 is barium chromate inhibited, Class C2 strontium chromate, and Class N non-chromate. MIL-PRF-23377K limits incidental hexavalent chromium in Class N to 5 ppm.

The part number encodes the choice. MIL-PRF-23377K's own example, M23377-1-C2-050C, is a Type I, Class C2, 50 cc touch-up kit; MIL-PRF-85582E gives M85582-1-C1-050C for a Type I, Class C1, 50 cc kit. Larger kits use designators such as 004Q for a 4 quart kit.

Selected MIL-PRF-23377K requirements, useful when you review a paint shop's qualification or a failure:

Moving from C1 or C2 to Class N is the usual route to a chromate free primer. It is a qualification decision for the design authority, because corrosion performance, filiform behavior and repair procedures are part of the qualified system.

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Polyurethane topcoat: MIL-PRF-85285

MIL-PRF-85285E is organized by VOC limit and use, then by formulation. Select the type your air permit and application allow, then the class.

Class H is a high solids formulation and Class W is waterborne. The part number adds the AMS-STD-595 color and kit size: the spec's example M85285-1-H-11136-050C is a Type I, Class H, gloss red (color 11136), 50 cc kit. Qualification panels are topcoated to 1.7 to 2.3 mil dry film thickness, adhesion must rate 4A or better by ASTM D3359, and thinning must not push the coating over its type's VOC limit. A topcoat over a 0.6 to 0.9 mil primer therefore lands in the range of roughly 2.3 to 3.2 mil total for a single system, which is a useful sanity check against a paint shop's thickness readings. Type II is the support equipment type; see our ground support equipment page for how finish fits into a GSE build.

Chromate free and CARC systems for ground equipment

Tactical ground equipment, and some aviation and support assets, use the chemical agent resistant coating (CARC) system: a lead and chromate free primer under a CARC polyurethane, applied and inspected to MIL-DTL-53072.

• MIL-DTL-53022F primer is flash drying, corrosion inhibiting epoxy for ferrous and nonferrous substrates. Type IV is the default and is qualified to 1,008 hours salt spray and 30 cyclic corrosion cycles; Type VI to 1,512 hours and 50 cycles; Type V is a touch-up kit. Class L allows 340 g/L VOC and Class U 250 g/L.
• MIL-DTL-53039E topcoat is a single component, flattened aliphatic polyurethane for tactical equipment, free of lead, cadmium and hexavalent chromium. Types run by VOC: III at 180 g/L, IV at 120, V at 60, VI at 0, IX at 420, and VIII for portable touch-up kits (aerosols up to 420 g/L).
• Colors are fixed by the spec, for example Green 383 (34094), Tan 686A (33446), Black (37030), Aircraft Gray (36300) and Field Drab (33105).

MIL-DTL-5541F notes that compatibility problems have been reported between conversion coatings and certain CARC products, so a CARC job on aluminum should name the pretreatment and confirm it with the coating supplier. Ground vehicle and weapons system buyers can find program context on our defense systems page.

Dry film thickness and adhesion testing

Dry film thickness (DFT) is measured nondestructively and per coat. MIL-DTL-53072F names magnetic gauges to ASTM B499 on steel and eddy current gauges to ASTM B244 on nonferrous metals, and ultrasonic gauges on composites, where they can separate primer and topcoat layers.

Three rules from MIL-DTL-53072F matter at inspection. The minimum applies to each coat, so a thin primer cannot be made up by a thick topcoat. Rejection is not made on the upper limit alone, but excessive primer thickness slows cure and causes adhesion problems. On rework, aircraft coating thickness (existing plus new) is limited to 8 mils on metal and 10 mils on composites.

Adhesion is checked with the ASTM D3359 tape test. MIL-DTL-53072F requires at least two coupons or parts per day of production, tested after 168 hours of drying or a force cure, using Method B cross cut with a 6 line pattern at 2 mm spacing and tape giving at least 80 ounces of adhesion; the average of three readings must be 4B or better. Above 7 mils of CARC, Method A (X cut) is used if the procuring authority permits, with 4A or better. Primer and topcoat specs use the 4A rating in qualification. Ask for adhesion and DFT results on the paint cert, not just a statement of conformance; our inspection and metrology page covers how gauge results should be reported.

Color numbers: FED-STD-595 and AMS-STD-595

Government colors are five digit numbers. FED-STD-595C was cancelled on 14 February 2017 and superseded by SAE AMS-STD-595, which SAE first issued in October 2015 and revised to B in May 2026. The numbering carried over, and drawings citing FED-STD-595 colors are still common.

• First digit is gloss: 1 is gloss (60 degree gloss 80 or more), 2 is semigloss (30 to 45), 3 is flat (6 or less).
• Second digit is color group: 0 brown, 1 red, 2 orange, 3 yellow, 4 green, 5 blue, 6 gray, 7 miscellaneous (black, white, gold, silver, violet), 8 fluorescent.
• Last three digits identify the color, sequenced from light to dark.

So 17925 is a gloss white, used in MIL-PRF-23377K as the topcoat on Type I test panels, and 36375 is a flat gray, used there over Type II primer. FED-STD-595C required color matching against physical chips, not fan decks or color books, under specified light sources. For acceptance, cite the color number and the chip standard on the drawing, and for camouflage coatings remember the color chip is not the whole requirement: CARC and low IR primers also have infrared reflectance limits in their own specs.

VOC rules and the paint shop's permit

Coating choice is constrained by air rules as well as performance. At facilities covered by the Aerospace NESHAP, 40 CFR 63.745 limits organic HAP and VOC content, less water and exempt solvents, as applied:

The military spec VOC caps sit at or below those limits: 340 g/L for both epoxy primers and MIL-PRF-85285 Type II, 420 g/L for Types I and IV. State and local air districts can be stricter, so ask the paint shop which rule its permit cites before you specify a higher VOC type, and do not let anyone thin a coating past its type's limit to make it spray better.

What to call out on the drawing or PO

• Pretreatment spec, type and class (chem film or anodize, and seal condition if anodized)
• Primer spec, type and class, for example MIL-PRF-23377, Type I, Class N
• Topcoat spec, type and class, and the AMS-STD-595 color number and gloss
• DFT range for each coat, and total, with the gauge method
• Adhesion test method, rating and sampling, plus witness panel requirements
• Masking for grounding points, bearing bores, threads and fastener holes, shown on a view
• Cure time before handling, packing and shipping
• Chromate free or hexavalent chromium restrictions, and whether DFARS 252.223-7008 applies
• QPD product names and batch numbers on the cert

Sequencing paint after heat treat, plating and NDT is covered on our special processes page, and paint cost drivers are on the special process cost page. Back to the coatings library.

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Related

• Chemical Conversion Coating to MIL-DTL-5541: Engineer's Reference
• Anodizing Aluminum to MIL-PRF-8625: Engineer's Reference
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• Aerospace Surface Finishing: Specs, Callouts and Pitfalls

Sources

• EverySpec: MIL-PRF-23377K, Primer Coatings: Epoxy, High-Solids (7 June 2012)
• EverySpec: MIL-PRF-85582E, Primer Coatings: Epoxy, Waterborne (16 October 2012)
• EverySpec: MIL-PRF-85285E, Coating: Polyurethane, Aircraft and Support Equipment (12 January 2012)
• EverySpec: MIL-PRF-85285E Notice 1, validation (13 October 2016)
• EverySpec: MIL-DTL-53039E, Coating, Aliphatic Polyurethane, Single Component, Chemical Agent Resistant (16 May 2013)
• EverySpec: MIL-DTL-53022F, Primer, Epoxy Coating, Corrosion Inhibiting, Lead and Chromate Free (1 December 2019)
• EverySpec: MIL-DTL-53072F, CARC System Application Procedures and Quality Control Inspection (31 May 2017)
• DLA ASSIST copy via ibiblio: FED-STD-595C, Colors Used in Government Procurement (16 January 2008)
• EverySpec: FED-STD-595C Notice 2, cancellation superseded by SAE AMS-STD-595 (14 February 2017)
• SAE Mobilus: AMS-STD-595 Colors Used in Government Procurement (revision history)
• Cornell LII: 40 CFR 63.745, Aerospace NESHAP primer and topcoat application standards
• HDIAC Technical Inquiry 2018-3809: common protective coatings for aircraft