Bare Alclad metal (Airplane)

G

gst124

In planning stages for paint on a 7 year project nearing completion. Vans RV-7 that is currently bare aluminum. Skins have a thin layer of AlClad that seems to be an occasional issue based on my limited research. Was planning on scuffing with a Maroon Scotchbright pad and soap, followed by a degreaser and maybe a acid treatment prior to spraying a DTM epoxy primer. Considered an Alodine treatment first, but does not seem to be necessary in the limited research I have seen. Any recommendations on systems for prep would be greatly appreciated. Back to my actual question, I was thinking about spraying epoxy primer on everything and plan on a base coat at some point in the future after a light sanding. I realize this may not be the correct way to go about it, and asking for advice. Should I spray and epoxy primer and add a layer of sandable after? The individual parts may sit for months to year prior to putting down a base coat.
 
#1 nix the acid treatment. dont ever do that before epoxy. you can leave in epoxy for as long as you want but before you basecoat you will need to sand and reshoot a thin sealer coat of epoxy right before your base.
 
Depends on your topcoat. All of my production work either gets chromated or anodized before paint, 99.9% gets masked so the inside stays conductive. There are paint systems that require you to spray over bare aluminum that I cannot use. Alclad is neat stuff, if its 2024 there is more copper in it for strength, but it smuts up faster than 6061 if you treat it with acid and as soon as it dries, it wants to protect itself by creating a new oxide layer. That is why its better to avoid it. There are so many safe RoHS chromates out there now you can probably spray it on and rinse it off, after you do the scuff pad all over, but only if your paint supplier recommends it. There are reasons some only want it painted over certain scratch bare metal.
 
#1 nix the acid treatment. dont ever do that before epoxy. you can leave in epoxy for as long as you want but before you basecoat you will need to sand and reshoot a thin sealer coat of epoxy right before your base.
Just because I am a newbie, do you sand the epoxy with something like 400 grit dry?
 
Depends on your topcoat. All of my production work either gets chromated or anodized before paint, 99.9% gets masked so the inside stays conductive. There are paint systems that require you to spray over bare aluminum that I cannot use. Alclad is neat stuff, if its 2024 there is more copper in it for strength, but it smuts up faster than 6061 if you treat it with acid and as soon as it dries, it wants to protect itself by creating a new oxide layer. That is why its better to avoid it. There are so many safe RoHS chromates out there now you can probably spray it on and rinse it off, after you do the scuff pad all over, but only if your paint supplier recommends it. There are reasons some only want it painted over certain scratch bare metal.

Well, crap. Now you have me going back and looking up Zinc Chromate Primers etc like you see in the production planes. I know that is the "right thing to do", was just hoping that I could get away with automobile finishes. I guess if it took me this long to get it finished, I should take the time to paint it right.
 
Order small batch of epoxy. Treat a scrap piece. Let it cure & then beat on it with a hammer.
I exoect it to pass torture test.
 
Order small batch of epoxy. Treat a scrap piece. Let it cure & then beat on it with a hammer.
I exoect it to pass torture test.

I highly doubt it. Alclad is basically aluminum foil honeycomb glued between a top and bottom layer of sheet.
 
2 quart epoxy kit to test ain't much compared to building a plane lol.
And it'll surely find a use if it's a no go.
 
I know Barry wrote about getting certified or something with Ford and their aluminum body panels, so its most probably going to work. I did not mean the epoxy would not hold up, I would think the hammer would hurt the alclad.
 
I highly doubt it. Alclad is basically aluminum foil honeycomb glued between a top and bottom layer of sheet.
Alclad is a rolled layer of pure aluminum on both sides of a sheet of alluminum alloy. Its for corrosion resistance in aircraft.
When I worked repairing aircraft, standard procedure was to Alodine then use epoxy then use single stage color.
Alodine is a chromate coating and doesn't add any film build to the part, it also helps with adhesion. If you decided to use it, you would need to ensure the epoxy you use is compatible.
 
If I'm understanding correctly, I would wait until you had topcoat in hand and ready to spray before putting anything on it. Otherwise you create a lot of extra work by putting an initial coat of alodine or sealer and having to hand sand the whole thing again later to reseal before topcoat. And I hate rivets...
 
My thought was that the epoxy primer would help protect the skins while waiting in storage for final assembly. Was also hoping that it would take some of the labor out of the final painting. Seems like most airplanes are simple single stage paints, but with the added step of prepping and priming the skins, it seems like it could quickly become a large job. It is also much easier to paint prior to assembly. Once you have it all together, it is a bit more difficult to put the fuselage in a Rotisserie so I don't have to paint on my back.
 
Some people say not to spray the topcoat prior to assembly as there is too much of a chance of damage while putting it together. Im just researching all my options and trying to determine the best course of action. Most people end up saying, "Screw it, finish the plane and pay for a professional paint job" and that might end up being what I have to do, but figured if I could build a plane, I should be able to paint it.
 
Alclad is a rolled layer of pure aluminum on both sides of a sheet of alluminum alloy. Its for corrosion resistance in aircraft.
When I worked repairing aircraft, standard procedure was to Alodine then use epoxy then use single stage color.
Alodine is a chromate coating and doesn't add any film build to the part, it also helps with adhesion. If you decided to use it, you would need to ensure the epoxy you use is compatible.

What alodine does is not allow the aluminum to start to protect itself again by starting to form that white dust coating you see on electrical enclosures all over the country. That dust is pretty much the same problem people have when they do not properly clean ospho, other than you cant see it. The best part of it, is you apply it right after a cleaning and deox stage when the part is still wet, where you clean the hell out of aluminum, you have to let it completely dry before getting to epoxy, and sometimes that is too long.

I am sure Barry will give you an honest answer either way about his Ford aluminum resurfacing dealings. They would all be the same. With the military work we do, its MIL-PRF-53022 over chromated aluminum or MI:pRF-23377 is the better choice that sticks to anodize too.
 
With the military work we do, its MIL-PRF-53022 over chromated aluminum or MI:pRF-23377 is the better choice that sticks to anodize too.

Can you put a single stage urethane over the MIL-RF-2377 or are you putting Enamel?
 
yeah, they call it moisture cure, but its air dry polyurethane. The military airplanes get MIL-PRF-85285 topcoat when its gloss. We mostly work with the ground based stuff and the chemical agent resistant coatings dull camoflage. They claim the airplanes dont need the CARC stuff since they are up so high, so I guess they dont think they will ever have a chemical attack them at an airfield.

I was reading that American was going back to not painting their wings anymore, I guess the paint they were using was cracking and causing too much maintenance. Also read about aluminized primer other commercial air craft use, so there are stress and flexibility issues with the forces a wing goes thru. I know members here will trust automotive paint on anything, but sometimes you start getting into different parameters and environments that just plain make it a bad idea.
 
Just to revisit this thread, I am thinking about a layer of epoxy primer and then since it will sit for some time, topping that with a 2K primer to make the sanding (etc) easier when it comes to top coat time (probably some time later). Does that should more reasonable than leaving it in Epoxy Primer for a long time? Seems like the 2K will "stick" to the epoxy if applied in the window of time before complete cure and also give me a much better sand-able medium when I choose the final colors for the plane.
 
I would just ask where will it be sitting. Outside in the UV then 2K, inside, covered up, I would leave it in epoxy. I would rather spray another coat of epoxy to start up again than sanding off the 2K. There are just too many things with stress and maybe G forces that I dont understand wings go thru in their lifetime so would want as little on as possible.
 
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