Aluminium corrosion / prep.

R

rottenlungs

Member
Hi all

I am finally making good progress on the respray of my '75 NZ 3500. I have one door left to prime then all the steel panels will be rust free. I have got to the point of being ready to strip and prep the bonnet and boot. Both have a number of areas of white powdery corrosion where the paint has peeled away.

I am taking the external surfaces of all panels back to bare metal.

I am a bit unsure on 1) how best strip the paint without damaging the aluminium and 2) what prep is required.

For the stripping of the steel panels I have been using paint strippper followed by a sand with 80 grit to remove any remaining paint. I then give the panel a coat of Plastikote rust killer. I then put a 1k dulon primer over the top. I did a test wing about 18 months ago and it looks remarkably good so fingers crossed.

For the ally panels I was planning to use the paint stripper again. I suspect that 80 grit is probably too rough for the aluminium and was thinking that a 120 grit would be a little more gentle. Are there any corrosion inhibitor products I should put on the panel or do I just put the etch primer straight onto the metal.

Any advice / recommendations very gratefully received.

Thanks

James
 
I would say it's just etch primer straight onto the clean ally. Obviously you want it as clean as possible. Ally starts to oxidise almost immediately after cleaning, so it's a good idea to apply the etch primer as quickly as possible.

I agree, 80 grit is probably too coarse, and just make sure your paint stripper is safe on ally, some aren't.
 
Your right, 80 grit is far too course for aluminium, but 120 or 180 which I would use, would be fine. I would still go over the panel once again with 320 grit before wiping the panel over with a degreaser prior to re-priming it with a self etch primer. My personal choice would be to go over the etch with a 2k high filler primer to give the panel a good protective hard coat before final paint.

Clicky link* http://mipa-paints.com/gb/product/prodi ... kt332.html
 
Hi

Thanks for the info.

I normally wash the panel with water when I finish the paint stripping and sanding. Given the speed at which the aluminium oxidises am I better off just going straight to the panel degreaser and not getting it wet with water?

Cheers

James
 
I think the overestimation of corrosion speed may set you wrong, Aluminium oxidizes pretty much instantly when you sand it so there is no way other than sanding the stuff in an oil bath and then the instant you clean it you will have an oxide coating. In fact the only reason you can use aluminium is because the oxide coating stops it from vaporizing before your eyes.

Wet sand wash then wipe down with thinners then etch / prime then paint.

If you were keen you could get the aluminium treated / plated with passivated chromium oxide that is the silver goldy blue surface colour you get on some aluminium item, that will give you a furthutr level of protection but i think you would need to find a big bath for bonnets and boots.

Graeme
 
We use Plascon Epiwash Strontium Chromate epoxy primer before final colour on our helicopters and they fly offshore mostly with minimal corrosion issues.
 
Thanks again, gentlemen.

I remember the greeny / yellow aluchrom (I think it was called) coating on the aircraft at the British Aerospace factory where the old man used to work. However, I reckon etch primer should be enough. Aviation-grade coatings on my pet Rover might almost be over-capitalising!

Changing the subject slightly, anyone know a good supplier for spire clips and screws, as well as the trim clips for the side strips?

Cheers

James
 
Look into your local marine grade paint suppliers too for good primers that will withstand just about anythng you throw at them, especially road salt etc...
 
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