I have been trying to work out a process for the priming, getting ideas from the Dueck book "Sheet Metal Techniques". Because of the coastal environment, I find it is important to give the internal parts of the wing as much corrosion protection as possible without compromising weight.
The process (using nitrile gloves, full face respirator with organic fumes cartridge filters and positive air flow via ceiling shop fans and outside incoming air):
(1) Clean and wipe down parts with alcohol-based cleaner for initial removal of any oils. Initially I was using lacquer thinner for this purpose, but the stuff is just too caustic. Alcohol seems to work fine, especially when followed by the phosphoric acid etching.
(2) Etch the parts in a bath of undiluted Bondrite C-IC 33 Aero aka "Alumiprep" for about 30 seconds to a minute. Transfer to a water bath.
(3) Transfer to a bath of Bondrite M-CR 1201 aka "Alodyne" for about 30 seconds or until the aluminum as a gold color. transfer to a water bath. Note: using 2 separate water baths, one for each process, in order not to mix chemicals.
(4) Allow the parts to dry. Made a small mark on each side with a sharpie (for example "port" or "stbd") to gauge the thickness of the primer coat. Sprayed a LIGHT coat of SEM self-etching primer (I have done tests on numerous primers and found SEM to be the most adhesive, with a superior spray fan.) If the sharpie marks become invisible, coat is too heavy. Trying to do a very light "piss" coat for reasons of weight without being tempted to put on more. This can be difficult.
(5) After primer is dried, assemble the rib shells and stiffeners by riveting 4 AN 470-3-3 rivets for each rib. Done!
**P.S. This process has worked so well that I decided to strip the previous ribs I had completed, including disassembling and stripping the primer off them in order to re-do it this way.
NOTE: stripping with EkoStrip works wonders on SEM primers and is less toxic because it is water-based.