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doctornigel

Active Member
I just finished priming the ribs, spars and other misc. parts of the vertical stabilizer. I used Al prep, alodine, and then the two part epoxy primer. I know it's probably overkill but I live beachside in Florida and if you listen real hard you can hear your car rust. I haven't done the skin yet, I want to prime the interior and not the exterior, I'll let whoever paints the exterior do it. I just can't figure how to do the Al prep and alodine without getting the exterior. And if it gets on the blue plastic I'll feel obligated to remove it for potential corrosion. What does everyone recommend, Al prep, alodine the whole part, sans blue plastic, and then prime the interior, or what? Will it make the plane harder to paint later?

If I alodine the exterior without priming, it'll look like I gold plated the plane. :D

Thanks all.
 
Aaaah, the never-ending primer debate!

Bear in mind the skins are already protected to an extent by the Alclad, so I think you may be over-killing somewhat. I scuffed with Scotchbrite, cleaned with sugar soap, degreased with thinner and then sprayed with a 2-part etching primer. There was little/no splatter to the exterior.

Once the section is complete, I think the recommendation is to remove the blue plastic. Yeah, I know the checker effect looks cool - thinking about using it for my final paint scheme (not really.........)

Good luck with the build. I'm not very far ahead of you, but when those first couple of pieces come off the production line it's a real rush. The HS is a blast - a 12ft piece of aeroplane! :D
 
What you can do is brush the alodine on the interior of the skins which is really the only practical way to do it IMO. You won't get the same uniform color from brushing as you did from dipping, but I think that's mainly cosmetic and you're priming over it anyway. Some alodine will probably get on the exterior around the edges and rivet holes, but it won't hurt anything and won't effect exterior prep and painting latter on. Since you will not have prepped the exterior it might not even stain (I'm using Sanchem and not alodine so take this with a grain of salt), but if it does so what. At worst, you'll have some gold colored blotches that will also get painted over.
 
Spray it (?)

I spoke to an A&P friend about this last month and he suggested using one of those pump up sprayers to apply alumiprep / alodine. Just spray it on making sure to keep the surface wet, and then rinse it off. Sounds easier than the rubbing it on with a rag I did to our fuel tank skins. If I ever need to alodine a skin again I plan to give this method a try. For all the other skins besides the fuel tanks I lightly scuff the interior prior to dimpling, vacuum the majority of the dust off, and then when I'm ready to prime it, wipe it down with acetone until the cloth comes clean, and then prime. I'm curious to hear other methods as well.
 
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Whether you prime or not, you will need to fight corrosion in a salt water environment. My CAP Squadron on Kauai uses ACF-50, although I've heard good things about Boeshield. I left the AlClad on mine but the QB portions will already be primed. I don't care because there will be ACF-50 inside the airplane on the first flight.
 
Hey, Doc,

I see I live just up the coast from you a few miles. Well, up the coast and back West over the Pineda. I just got started on my wings for the RV9, so we are close in what we are working on, though your project is a bit more involved than mine.

Anyway, I have debated the priming thing and I think I am going to cut back on what I do relative to what I did on the empennage. There, I primed everything. My changing my mind is based on an experiment someone in the Merritt Island EAA chapter did. He left some aluminum outside a couple of years ago (a scraped piece of a stabilizer or something) and, even with frogs and other critters living in it, he said the aluminum looks as good today as it did the day he got it.

What I am doing now is priming those areas where metal meets metal, and where water might reasonably collect. I think a lot of builders go ahead and use high tech primers all over because we want to be extra safe and if we don't prime then, well, we think that others might say we are not good builders.

But, what I did yesterday was finish deburring my wing ribs, then I sparyed the front and aft flanges with rattle-can zinc chromate (available at Ace). Since the main spar is already protected, I will also spot prime the mating locations on the rear spar, then I will rivit it all up. Prior to installing the lower wing skins, I will prime the lower flanges of the ribs, and I will prime the entire lower skin. I see no reason to prime the upper skin or upper rib flanges (even though I will probably spot prime the upper rib flanges as those surfaces have been scuffed a bit), as any water that forms on those surfaces will quickly drain away.

Now, sure, a part of me is still wondering if I should take greater measures "just to be safe". When I have the ribs attached to the spars, it will be a little tempting to shoot it all with primer, as it will be so easy to do and since I already have the primer, which cost well over $100 for a gallon that I really don't want to waste. Still, that is a sunk cost and why carry about pounds of primer I don't need?

That, anyway, is my current plan. Now, tonight, I might change my mind again, and if anyone sees any flaws to my logic, please speak up.
 
I am sceptical

I gotta comment on this as I find it highly unlikely that a piece of aluminum placed outside (in the rain ?) in a Florida Island environment looks as good as new after several years. It could be, but it just don't sound right.

I live in Portland, Oregon (rains so much we actually have moldy people) and I am going to put some scrap airplane bit outside today and start my own oxide experiment.


Rust never sleeps (and aluminum oxide never goes on vacation ;) ).

Kerry Stevens
 
I' ve heard many times that priming and paint adds weight. Of course, that's true!!!

But, my question is: How much weight is added?

If anybody can answer those questions below, I'll be thankful.

How much weights:

a) Priming all interior
b) Priming all exterior
c) Exterior base coat
d) Exterior top coat
 
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