Two primers at a glance
Where to buy| Item | Desoprime HS CA7233 | Desoprime CA7502 |
|---|---|---|
| Type | Military epoxy primer, exterior | Chrome-free epoxy primer, exterior |
| Qualified to | MIL-PRF-23377 Type I Class C2; MIL-PRF-53039; MIL-PRF-64159; MCS 9053 | BMS 10-72 Type VIII, IX, X; CMS-CT-201; PWA 36525 (OEM specifications) |
| Mix by volume | 1 base : 1 activator | 4 base : 4 activator : 1 thinner |
| Pot life | 5 h (13-18 C), 4 h (18-23 C), 3 h (24-29 C), 1.5 h (over 29 C) | 4 h at 21-25 C |
| Induction | None over 29 C; 30-60 min (18-23 C); 1-1.5 h (13-18 C) | 2 h (13-21 C), 1 h (22-26 C), 30 min (over 27 C) |
| Dry film | 15 to 30 microns (0.6 to 1.2 mil) | 12.5 to 30 microns (0.5 to 1.2 mil) |
| Topcoat window | 2 to 72 h | See the sheet |
| Service range | -54 to 177 C | -54 to 177 C |
| VOC (CA7233, mixed) | 340 g/L | See the sheet |
PPG Aerospace data sheets. Typical values, not for acceptance criteria, says PPG. Check the current QPL and the SDS.
MIL-PRF-23377 epoxy primer
What it is. A solvent-borne, two-component epoxy primer specification. Desoprime HS CA7233 is qualified to Type I Class C2 (PPG).
What it is for. Corrosion-inhibiting primer on treated aluminium and other metals; PPG recommends aluminium treated to MIL-C-5541 or equivalent.
How it is used. Shake the base, stir the activator, add activator to base and stir 10 minutes; condition the materials 24 hours at 13 to 35 C first; allow the induction time; spray a single medium coat to 15 to 30 microns; ground aircraft and equipment (PPG).
Life and cure. Pot life 1.5 to 5 hours depending on temperature. Dust free 20 to 45 min, tack free 45 to 75 min, topcoat after 2 hours and within 72 hours, full cure 7 days (PPG). Shelf life 12 months to the specification, 24 months to the PRC-DeSoto standard; store at 5 to 35 C.
Safety. Flash points on the sheet: base 16 C (60 F), activator -4 C (24 F). Read the SDS; PPG asks for it before use. Flush equipment with the cleaners PPG names (Desoclean 45, CN20, CN44).
Specification. MIL-PRF-23377 (types and classes in the document); check the current QPL.
Equivalents. PPG lists compatible topcoats, including MIL-PRF-85285. Other makers' primers qualified to the same type and class are candidates only where the SRM allows.
MIL-PRF-85582 waterborne epoxy primer
What it is. The military specification for waterborne epoxy primer, the lower-solvent alternative to MIL-PRF-23377. We did not find or read a data sheet for a MIL-PRF-85582 product, and give no figures.
What it is for. The same role as 23377: corrosion-inhibiting primer under topcoat.
How it is used. Read the maker's sheet for the exact product: mixing, induction and film thickness vary.
Life and cure. From the product's data sheet.
Safety. From the SDS.
Specification. MIL-PRF-85582; check the QPL on ASSIST QuickSearch.
Equivalents. Do not swap a 85582 primer for a 23377 one on the grounds of colour or brand. The SRM names which.
Chrome-free primers
What it is. Epoxy primers without chromate. PPG's CA7502 is an example: its sheet lists OEM qualifications rather than MIL-PRF-23377.
What it is for. Exterior aircraft primer and detail parts, urethane-topcoat compatible (PPG).
How it is used. Mix 4:4:1 by volume; the primer should look translucent and should not be applied to full hide (PPG).
Life and cure. Pot life 4 hours at 21 to 25 C. Condition materials 24 hours at 13 to 35 C first.
Safety. SDS.
Specification. See the table.
Equivalents. Not interchangeable with a chromated 23377 primer unless the SRM says so.
Zinc chromate primer in older documents
AC 43.13-1B refers to zinc chromate primer among organic coatings (par. 6-40) and to two coats on exposed fittings. It is a historic material in many manuals; the SRM names today's primer.
Questions people actually ask
Do I prime the rivet holes?
Yes. AC 43.13-1B par. 6-134e says to drill, countersink, surface-treat and prime every rivet hole before the doubler goes on.
How long before the topcoat?
For CA7233, topcoat after 2 hours and within 72 hours (PPG). Other primers differ.
Is chrome-free primer the same as MIL-PRF-85582?
No. Chrome-free describes the pigment; 85582 describes a specification. The CA7502 sheet does not list 85582.
Limits — when NOT to use this
What the sources support, and no further.
- Two PPG sheets. Figures belong to those products.
- No MIL-PRF-85582 data. We did not read a sheet or the specification.
- Type and class definitions are in the specifications, which we did not quote.
Where to buy
Distributors coming soon.
Sources
- FAA AC 43.13-1B CHG 1, Chapter 6 (corrosion control, safety precautions, finishes) — Pars. 6-90 (safety precautions), 6-134 to 6-136 (finish, conversion coat, 48 hour rule, fasteners), section 4 (corrosion preventive maintenance, MIL-C-16173 Grade 4); par. 5-63 (cleaner types).
- PPG Aerospace, Desoprime HS CA7233 Military Epoxy Primer, Technical Data Sheet — MIL-PRF-23377 Type I Class C2, mix ratio, induction, pot life, film thickness, dry times, VOC, flash point, shelf life.
- PPG Aerospace, Desoprime CA7502 Chrome-Free Epoxy Primer, Technical Data Sheet — Chrome-free primer: mix ratio, pot life, film thickness, qualifications.