Prep for aluminum service body? Epoxy and grit?

S

Speed Barn

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I need to prep this brand new aluminum service body with peeling topcoat. It is aluminum, and will be color matched silver to a new GMC. Any input on treating the metal, or just go straight to epoxy? I've never had to deal with this over aluminum.
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Seeing that it's peeling I would either sand with 180 or if I could, media blast it.

If the former, I would sand it down as best I could using 180 grit on the DA and 180 by hand in the places I couldn't reach with the DA. It may take some time to do this so when you have it all sanded, go over the whole thing again and get it in primer ASAP. Aluminum oxides immediately so you have approximately 12 (ideal) - 24 (absolute max) hours from when you sanded to when you have to get primer on it. If it goes longer sand again before you prime. Goes without saying that you need to wipe it down properly as well.

If the latter, then prime it as soon as you media blast it. Should be able to go straight from blasting to priming without wiping it down. If you handle it any then you would need to wipe it down. Try to avoid that as wiping down something freshly blasted is a pain. Your wipes will catch on the surface and lint up.

Third option would be using a system like Alodine or other acid. If you go that way read the instructions and follow them. You need to neutralize the surface before applying epoxy.

If that doesn't answer your questions, keep asking and I'll try to help. :)
 
I should add because aluminum is softer than steel you shouldn't use anything coarser than 180 when sanding or you will start to remove metal. 180 grit scratches in aluminum are the equivalent to 80 grit scratches in steel.
 
If media blasting, you have to find someone who knows about how to work with it. Years ago we had a guy get a big aluminum bodied van blasted by a guy who used coal slag at high pressure. I tell you you've never seen such a mess, the door would barely open and close anymore because of how stretched and bellied-out the aluminum was. Low pressures and oblique angles are the way to go with aluminum afaik.
 
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