Priming Aluminum

[mmarien]

I see a lot of aluminum being primed before assembly. I spoke with my neighbor that built a Sportsman 2+2 on amphibs. He primed the inside of his wings because it would be on water a lot. The outside of the wings were bare aluminum. I asked my neighbor mechanic if he was going to prime the J3 wings he was building. The spar and ribs are aluminum. He said he wasn't because they are ALCLAD. I'm pretty sure the inside of my 1948 Luscombe wings are not primed. In fact, except for a couple painted stripes, the whole plane is bare aluminum. When I asked him about my Hatz ailerons he had a look. He said that they had enough air going through them that priming wasn't necessary, unless I lived by the sea.

To prime or not to prime. I'm kind of leaning towards not priming the insides of the ailerons. The three oceans surrounding me are about equal distance away. What are you guys doing?

[painless]

This is an age old question in home building. I built an RV and there’s actually a term for it....primer wars. Topics vary between whether to prime or not, need for alodinig, what primer is best.....

If you don’t prime Alclad aluminum, the airplane is still going to outlive you. Having said that, I still feel more comfortable with a light coat of primer at least where aluminum parts are riveted together. Moisture in there can still cause surface corrosion to start. I’m in the process of assembling my ailerons as well and plan to prime the inside with self etch primer. I’m using Mar Hyde from spruce, but my RV brethren have also used NAPA MS 7220 primer as well. Wash the part, scuff with scotchbrite pad, wash again, then wipe down with naphtha (Coleman lantern fuel) and hit it with primer. Relatively quick, easy step for piece of mind. No real weight penalty provided you apply a thin coat.

[mmarien]

Thanks for that Jeff.

In the last couple days I did see a couple cases where the paint didn't seem to stop the corrosion. My friends amphibs had a few places where the corrosion was under the paint. And the J3 Cub rebuild next door. He's redoing almost all the fairings because of corrosion under the paint. The J3 was a barn find so perhaps not normal circumstances.

I'm still in the air. As you say, the ailerons will probably far outlive me without any corrosion protection other than the ALCLAD.