Ask the Expert Question-and-Answer Archive

by Ron Joseph

February, 2006

Painting Aluminum - Is Sealer Required?

Q. Upon reading your web page http://www.ronjoseph.com/Q&A/B2001_painting_aluminum.htm I noticed the use of a sealer was not recommended in conjunction with a wash or expoxy primer. It is my understanding that a sealer will strengthen any top-coat. Would it be correct to say you do not recommend a sealer? if so why not? Thank you

A. If you use a wash primer when painting aluminum, followed by an epoxy primer followed by a polyurethane topcoat, you do not need to also apply a sealer. If you would like to apply a clearcoat polyurethane over the polyurethane color coat, you can do so but it doesn't strengthen the topcoat. It simply adds another layer of paint over the substrate. If you build too many coats of paint you run there risk of paint peeling; therefore, the axiom, "the more the better" does not apply here. You do need to have a minimum film thickness over the aluminum, but too much can be harmful.

By far the majority of aerospace applications do not have a clearcoat.

Finally, I must draw your attention to the fact that a wash primer is not the ideal for treating aluminum. Instead there are conversion coatings that do a considerably better job, but perhaps you do not have the facilities to apply a conversion coating. For more on these technologies please see the Henkel Surface Technologies, and Chemetall-Oakite web sites.

Best wishes,

Ron Joseph