(DL152279546231) wrote in message ...
I have been looking at Zenair's Ch 701 STOL and nowhere have I seen any mention
of treating the inside of the sheet alluminum for corrosion protection. I would
have thought spraypainting with green (zincoxide?) paint woudld have been
necessary

Only if it's going to be used as a floatplane on the ocean. Zinc
oxide (or zinc chromate, which is better but apparently causes cancer)
will offer good protection but adds weight.
Aircraft aluminum sheet has a thin layer of commercially pure
aluminum applied to each side of the sheet, amounting to about 2% of
the total thickness on each side, and pure aluminum will oxidize
almost instantly and form an inert layer that protects against further
corrosion for most applications.
Scratching through this layer is asking for trouble, so an
owner/builder needs to be careful about sanding and so on. Some owners
have destroyed airplanes sanding the paint off them. I was told
recently about an airplane that was sent to an autobody painter who
painted it and put it outside to dry. Wind and sand ruined the job, of
course, so he took a power sander and ground all the paint off and
repainted it. Took off much of the protective aluminum, and ground
flat almost every rivet head. A really expensive mistake.

Dan