Corroded aluminium - white and powdery - how to treat/finish?

[Northwards]

Hi folks,

I’m sure this absolutely must have been covered before, but I did a search for ‘aluminium corrosion’ and went through two or three pages of results without finding just what I was after.

I posted a question last weekend about repair panels for the lower front of a 90 rear tub ( the bit which is mounted to the chassis outrigger, and the seatbelt buckle brackets). Decision made to go for the YRM galved steel replacement panels.

I will need to cut out and replace some of the worst bits with new alu. sections, but for the rest, what’s the generally accepted way to deal with this? This will be to functionally rather than cosmetically give the alu. some protection.

My own thoughts would be to grind off the worst of it with a ‘scotchbrite’ flapper wheel, and then get into any nooks and crannies with a brass wire brush (leaving behind no steel fragments) - though it’s unlikely I’ll get into all the pitted dimples. Then etch primer, then some sort of top coat. As it’s not cosmetic, this could be anything from hammerite to underseal. Once all that’s done, I’ll bond/separate the alu. from the galved steel repair brackets.

So that’s what I reckon I’d do. But quite happy to hear of any other accepted/recommended approaches.

Thanks.

Donald

[Stellaghost]

31 minutes ago, Northwards said:

Hi folks,

I’m sure this absolutely must have been covered before, but I did a search for ‘aluminium corrosion’ and went through two or three pages of results without finding just what I was after.

I posted a question last weekend about repair panels for the lower front of a 90 rear tub ( the bit which is mounted to the chassis outrigger, and the seatbelt buckle brackets). Decision made to go for the YRM galved steel replacement panels.

I will need to cut out and replace some of the worst bits with new alu. sections, but for the rest, what’s the generally accepted way to deal with this? This will be to functionally rather than cosmetically give the alu. some protection.

My own thoughts would be to grind off the worst of it with a ‘scotchbrite’ flapper wheel, and then get into any nooks and crannies with a brass wire brush (leaving behind no steel fragments) - though it’s unlikely I’ll get into all the pitted dimples. Then etch primer, then some sort of top coat. As it’s not cosmetic, this could be anything from hammerite to underseal. Once all that’s done, I’ll bond/separate the alu. from the galved steel repair brackets.

So that’s what I reckon I’d do. But quite happy to hear of any other accepted/recommended approaches.

Thanks.

Donald

Barring cutting out and tigging back in you've got it all covered regards Stephen

[Gazzar]

I'd put an anti corrosion wax on top. And avoid hammerite. Get something zinc rich. 

[Northwards]

Thanks Stephen - as I said not so long ago, there will be an enormous gulf in technical ability between thee and me! No tigging going to happen here I’m afraid, but good to know I’m on the right lines.👍

Gazzar - hammerite was almost a figure of speech 🙂 something I rarely use. Would you use zinc rich stuff even on aluminium? I think we did get a tin of zinc rich stuff before starting the job, so that would certainly be handy. There will definitely be some sort of physical barrier between the two metals - a PVC sheet, or a thin closed-cell foam gasket. I’ve been here before where you do something and think: “that’ll be OK” and then have to take it apart again fairly soon to do it all properly. That lesson’s well learnt.

Thanks for your replies. 

[miketomcat]

I have in the past had good results cleaning it as you've said then painting with por15 before continuing to paint the whole car (etch, filler primer and top coat). This lasted for 6 years with no come back (I sold it at that point). The truck was recently for sale again and hadn't been repainted so I assume it's still going strong.

Mike

[Stellaghost]

51 minutes ago, Northwards said:

Thanks Stephen - as I said not so long ago, there will be an enormous gulf in technical ability between thee and me! No tigging going to happen here I’m afraid, but good to know I’m on the right lines.👍

Only been tigging a couple of years myself.....

Good excuse to buy a new tool and learn new skills.......... And close that gulf you keep talking about...I'm quite sure that gulf is not as wide as you think it is regards Stephen

 

[Gazzar]

I toy with the idea of getting a tig, but don't have time to do what I need to do at the moment.

[Bowie69]

I'd love one, especially for doing stuff not in steel for the little green thing...

Just can't justify the cost at the moment.

[Stellaghost]

27 minutes ago, Bowie69 said:

I'd love one, 

Santa baby..🎶...................

regards Stephen

[muddy]

1 hour ago, Stellaghost said:

Santa baby..🎶...................

regards Stephen

don't be welding in that singing outfit though!

[stevebus]

I had the same problem and to be honest, quite bad in places, but I was planning on removing all the paint on an old MOD wagon, to many coats of paint to count, green, black, green, sand colour and what ever else came through, no nitromors or any conventional paint stripper was working, I used a stuff called Starchem Synstryp, now whether the fact I didn't stop sanding till it was back to bare metal or this jollop had anything to do with it remains a mystery but I've never had any problems with bodywork since, no rot or powder, I might add it makes the original nitromors look like milkshake, it says on the instructions to wear gloves, goggles, breathing apparatus, I rarely do but with this stuff, it proper hurts, taking lumps out of me, it isn't cheap but I think would just about murder anything that shouldn't be there, but remarkably kind to the metal, hope this helps