I spent a lot of time reading up on the various aspects of corrosion protection. Many sources listed the inherent corrosion resistance of 6061T6 aluminum. The general consensus is that this alloy offers superior resistance compared to other aluminum alloys. Some builders report virtually no corrosion on 6061, others have reported signs of surface corrosion on the inside of skins and other large areas in as little as 6-10 years (that plane was tied down about 10 miles from the ocean).
My own research has lead me to the following conclusions:
My plan for prepping the aluminum will go something like this: Use lacquer thinner to remove all ink marks and printing from the parts. Using a spray bottle, spray parts with acid based etch solution (AFS Cleaner/Etch, PPG DX533 Cleaner/Etch, Alumiprep, ect.) and let sit for a couple of minutes. Scrub the parts with ScotchBrite pad (use gloves!) to abrade the surface and remove surface corrosion. Rinse with clean water and dry. Prime parts as soon as practical (within a couple of days).
Based on my priming strategy, my initial plan for priming interior structures is to purchase 12 spray cans of Tempo brand Zinc Oxide primer (Aircraft Spruce PN 7-9100). This should provide me with 300 sq. ft. of application (approximately 25 sq. ft. per can), and should cost less than $75. I feel this offers the best compromise between cost, simplicity, and performance.
For the exterior paint, I plan on using the AFS 1-part water-bourn Primer/Sealer, followed by AFS 2-part polyurethane color Top Coat. At the current time, I have no spray equipment and only experience spraying PolyFiber paint and products. I will continue to research and talk to other builders, and my choice of exterior paint may change.
Update: After completing the fuselage priming, the Zinc Oxide primer is really easy to use. It took me about 3-4 hours to prep all my fuselage parts with Alumiprep (acid etch), and then about 2-3 hours to prime the parts. I used 4 cans on the fuselage. At 12 oz per can, that is 48 oz of liquid primer. Once you subtract overspray and the weight of the solvent carrier, and there is probably only 1/3 of the weight left on the parts. That means I added a pound or two of weight, $30, and 1 days work to fully prime my fuselage. Sounds good to me!
You may notice in some pictures that ink marks have bled through the primer. In many instances the cause of the bleed through is failing to remove the old ink marks (part numbers, alignment marks, construction lines, etc) with lacquer thinner prior to scuffing the aluminum surface with a scotchbrite pad. The scotchbrite removes the top layer of ink as you scuff but leaves lots down in the pores of the metal. When the solvent from the primer hits the ink, it raises it from its' hiding places and bleeds it through the primer. The best way to prevent this is to 1) clean the ink from the part with lacquer thinner, 2) scuff with a scotchbrite pad, alumiprep etch, 3) rinse with water and dry completely, and finally 4) prime.
Ultimately, you will have to make up your own mind on priming, but I know how frustrating it was to get the same non-commital, "It's a personal choice" answer. The links below are some of the oppinions and information I found during my search on the internet. I place them here for information purposes only, and make no claim as to their accuracy.
EAA Chapter 1000 Corrosion Control Articles
Gary Liming's Zenith 801 Web Page - Corrosion
Andy Karmy: Priming his RV-9
Primer wars by Andy Karmy
Aircraft Painting - Solving the Mystery by Ron Alexander
The Priming Issue from Robert's RV-7 Website
DETCO Aircraft Coatings
Preparation and Priming - Just one view
Priming with PolyFiber Epoxy Primer
That Priming Thing... by Sam Buchanan
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Updated: 22 Jan 07