Primer - Corrosion Protection

[MikeS.]

The Panther is my first aluminum project so I have concerns about long term internal corrosion protection. I know that the Alclad surface will provide this protection so I’m only concerned about metal to metal contact areas like the individual spar pieces before assembly, rib/bulkhead to skin contact areas, etc. I want to minimize weight so I am not spraying primer on the open areas of the internal skin surfaces.

I have been to multiple websites to get some ideas and there seems to be a long debate on what product to use; Zinc Chromate, Zinc Oxide, Zinc Phosphate, SEM self-etching primer, and NAPA 7220 self-etching primer (Martin Senour product).

Cost and health issues aside (it’s a given that we want to be frugal and should all be using health protection) what are your product recommendations for a primer sealer: (A) aerosol can for small parts, (B) use in spray equipment for large parts like the spar.

As for application do you recommend: (A) clean the parts then spray; this leaves the Alclad protection untouched, (B) scuff the parts with a Scotch-Brite pad, clean, and then spray; it seems that this technique would break the Alclad protection. If “B” is chosen to what degree does the part need scuffing: Scotch-Brite General Purpose (red pad) or Ultra-Fine (gray pad)?

I don’t mean to beat a dead horse with this subject but I haven’t found a direct answer to the questions in the forum searches. My composite airplane projects were eons ago and there were limited aluminum and steel parts. The parts were either powder coated or I cleaned the parts and painted with Zinc Chromate from an aerosol can. Depending on where the part was going determined whether it was top coated with an epoxy primer and paint or just left with the Zinc Chromate finish.

Do all of the products listed above, or that you might otherwise recommend, provide a good seal to the primer to ward off moisture? Some primers actually absorb moisture and we don’t want that.

What say you?

Thanks - Mike