Ask the Expert Question-and-Answer Archive

by Ron Joseph

July, 2005

Painting Aluminum Aircraft Engine

Q. I have an application on an aircraft engine part that requires a protective paint coating for salt mist corrosion protection. Presently the unit is cleaned with isopropyl alcohol, then primed with epoxy primer (MIL-PRF-85582 or 23377) then spray painted with two coats of Benjamin Moore TT-E-489 Alkyd Enamel Gray Gloss Low VOC. The repair facility wants to eliminate the epoxy primer. Is there suitable one part substitute primer?

A. Painting aluminum is difficult at best and even the sole cleaning with isopropyl alcohol (IPA) is questionable. The proper treatment should include a chromate or non-chromate conversion coating. (Perhaps you are doing that but didn't state it in your email.)

Although the chromate pretreatment (Alodine, Chemfilm, and other trade names) has shown itself to be superior to the non-chromate pretreatments, hexavalent chromates are carcinogenic and many companies are moving away from them.

Since your only pretreatment is a solvent wipe with IPA, I would absolutely require the application of MIL-P-23377 or MIL-PRF 85582. The TT-E-489 gloss topcoat is an alkyd and is predominantly designed for decoration rather than corrosion protection. If you are looking for corrosion protection why are you not considering MIL-C-83286 polyurethane (aircraft topcoat)?

Best wishes,

Ron Joseph