Bondo and paint prep on aluminum

Ultradog MN

Well-known Member
Location
Twin Cities
There is a cast aluminum band on the front of this tractor I'm working on.
Has a couple of slight dings and scratches on it that I'd like to fix before I paint it. Will ordinary bondo work on aluminum? How about priming it so it will hold the paint. What would you use?
Thanks

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Adhesion to aluminum is a problem for most things. You would be better off to clean the metal with a solvent such as acetone or lacquer thinner and prime the metal with a primer suitable for aluminum and then apply the fiberglass filler. When aluminum oxidizes it secretes a substance which feels like oil. It's what turns your hands black when using an aluminum ladder. This oily substance is what makes aluminum difficult to paint and the reason for cleaning with a solvent.
 
(quoted from post at 08:59:59 02/29/20) Adhesion to aluminum is a problem for most things. You would be better off to clean the metal with a solvent such as acetone or lacquer thinner and prime the metal with a primer suitable for aluminum and then apply the fiberglass filler. When aluminum oxidizes it secretes a substance which feels like oil. It's what turns your hands black when using an aluminum ladder. This oily substance is what makes aluminum difficult to paint and the reason for cleaning with a solvent.

Stephen, I am pretty sure that Aluminum doesn't secrete anything. I am positive though that it will oxidize when left out in the weather. I am also positive that Aluminum oxide is black. I am also positive that nothing will stick to aluminum oxide, so yes it dowes need to be cleaned off but it is very easy to remove.
 
Rough up the area for filler with some 80 grit - to give it something to bite to. Apply metal etching primer. Work filler as normal steel.
 
What kind of paint and primer are you using on the rest of the tractor?

I would blast the aluminum, clean it with wax and grease remover and spray it with epoxy primer within a short time of blasting it. Don't give it time to oxidize. Filer should be applied over the epoxy.

That said, if you are planning to use an inferior paint system on the rest of the job, it wouldn't be worth it to buy product for one piece.
 
Thanks fellas.
I still don't know what to do with it.
Been thinking I'll talk to a body shop that works on the aluminum bodied Ford 150s and see what they use. Maybe have them prime this with whatever they use while they're painting something else.
 

They use epoxy, as I am suggesting. It may be cheaper to have them do it if you have no other use for a couple quarts of epoxy primer.
 

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