Paint the exposed zinc chromate surface?

[terrykohler]

I had access to a metallurgical lab when I built my plane and just to satisfy my curiosity, ran ASTM salt spray tests on bare aluminum, alclad, and a number of finishes. Zinc chromate over an etched surface provides virtually unlimited corrosion protection, even without a secondary coating on top.
Terry, CFI
RV9A N323TP

[PTI Paint]

Terry,

Great point! The topcoat is mainly meant to protect with regard to weatherability, UV, cracking and impact as well as provide aesthetics. All the corrosion protection you need is in the acid etching wash primer and primer over top