Ask the Expert Question-and-Answer Archive

by Ron Joseph

November, 2003

Paint Removal from Aircraft Skin

Q. We would like to use epoxy primer and polyurethane topcoat on our Fokker aircrafts. The base of the existing paint system is wash primer. Is it possible to remove the wash primer absolutely without starting any irreversible process in the skin of the aircraft? Will the alodine do its job after this wash primer removing process? Do we need this wash primer removing process?

A. If you are already using an Alodine process, I don't see a need for the wash primer. If the skin of the aircraft has been properly treated with Alodine and you have applied a uniform coating, then you should get the corrosion resistance and paint adhesion from this process. The only reason people use wash primers is in situations where they cannot apply a chromate conversion coating (such as Alodine, Chemfilm, etc.) on aluminum, or a phosphate coating on steel. Therefore, regardless of the paint removal process, you might want to experiment with Alodine only and see if you can successfully eliminate the wash primer from your painting operation. In fact, I have seen problems when both Alodine AND wash primer have been applied under an epoxy primer.

As to the paint removal process, if you are using chemicals, such as methylene chloride, NMP, benzyl alcohol or other paint removers there is a good possibility that the Alodine will not be affected. Since the Alodine is probably gold in color, you should be able to determine if the paint removal has also removed the conversion coating. It is always a good idea to experiment before you do the entire job. Find a small area on the aircraft where no harm will be done to the surface and nobody will see the results.