Removing 'Stains' from Aluminum Sheet

Finishes, paints and coatings

Removing 'Stains' from Aluminum Sheet

Postby Squamish » Sat Nov 14, 2020 7:18 pm

I am skinning my trailer with .040 5052 aluminum. After it was delivered the pallet was rained on. The sheets were separated by thin tissue to eliminate scratches in transit but unfortunately they 'stained' the aluminum leaving streaks. The discoloration may be from a mild chemical reaction (paper is acidic) or ? I experimented with a little Mothers car polish with very modest results that may be simply from the abrasives.

Any thoughts on materials or processes to remove the stains would be appreciated.

https://www.amazon.com/photos/all/galle ... 3234696011
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Re: Removing 'Stains' from Aluminum Sheet

Postby lfhoward » Sat Nov 14, 2020 8:42 pm

Sorry this happened. Try using rubbing alcohol, goo gone, or goof off. They are listed in increasing strength. I have used all 3 on my white 0.04 aluminum skins and they haven’t damaged the paint. Goof off was the only thing I could find that could remove sticky residue from the plastic protective sheets that baked on in the sun. Careful, goof off will melt your plastic gloves in short order!
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Re: Removing 'Stains' from Aluminum Sheet

Postby tony.latham » Sat Nov 14, 2020 8:49 pm

I think the "stain" is corrosion.

The folks that are experts with this issue are the Airstream restorers. Do a search on Youtube for "airstream polishing".

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Re: Removing 'Stains' from Aluminum Sheet

Postby Squamish » Sun Nov 15, 2020 5:55 pm

I do believe it is a form of corrosion caused by the acid in the paper. Portions of the sheets that merely got wet and had neither cardboard or tissue in contact have no defects. I appreciate the advice and will follow up with an airstream restorer. My wife says 'let it ride, it simply adds character'. I have added a lot of character elsewhere, so I may investigate a cure.
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Re: Removing 'Stains' from Aluminum Sheet

Postby Graniterich » Sun Nov 15, 2020 10:34 pm

Please let us know what you find!
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Re: Removing 'Stains' from Aluminum Sheet

Postby MickinOz » Sun Nov 15, 2020 11:53 pm

Ortho phosphoric acid removes the oxide layer on aluminium, and that's usually where the stains are.
Look for an proprietary aluminium cleaner that lists the active ingredient as ortho phosphoric acid or just phosphoric acid.

If you get one that also lists hydrofluoric acid as an ingredient, whatever else you do, wear rubber gloves.
HF gives me the shudders every time I think about it. It's usually only present in the 2 or 3% range, so it's probably safe enough, but still.
The Safety Data Sheet used to have this line under instructions for physicians: "excise the necrotic tissue". 'nuff said

Like all potential solutions to the problem, test on an inconspicuous area first.
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Re: Removing 'Stains' from Aluminum Sheet

Postby Squamish » Fri Nov 20, 2020 9:33 pm

Thanks for all the suggestions. I may opt for using airstream polishing techniques simply to give aluminum an even start to its longer term patinina. I will wait until the build is finished as I am sure there will be some scratches to blend. I am surprised at the softness of 5052 aluminum. Just look at it sideway and there is a scratch.

Thanks again.
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