Aluminum corrosion during storage

Finishes, paints and coatings

Aluminum corrosion during storage

Postby brett_x » Fri Jul 07, 2017 10:44 am

Hi all,
I've been working on a build since September, and that's when I bought some 4x8 aluminum sheets to skin my teardrop. I didn't get to that part of the build until now. Unfortunately, when I finally got my aluminum out of storage, it's badly corroded. I had 7 sheets stacked together, and only the top and bottom surface (the exposed sheets) are fine. Here's what it looks like:
149429

The main reason I want to use aluminum is because I want it to be nearly maintenance free and I like the mill finish. I had always thought that aluminum was the best option. I've tried cleaning it with various solvents, and it just isn't going to be worth the effort, so I've ordered new material.

So, I guess I don't understand aluminum. Can any one tell me why this happened? It's "only" a $175 mistake, so I'm not overly upset about it, I just want to make sure I do the right thing with the new stock and understand what happened.

I'll tell you what I know:
I bought it from a metal manufacturer near me- http://americansteelandaluminum.com and picked it up in their warehouse. They pulled it from their stock in the high bay (it was stacked). I had stored it for about a month outside, still stacked. It was under a canopy, but not really protected from the weather, so it probably got wet. When I took it off of my car - sheet-by-sheet - and stacked it on some sawhorses, the sheets seemed to have a chemical on them. It seemed / smelled like some kind of solvent. When my brother and I moved the sheets into my shed for winter storage, I noticed the corrosion, but didn't think it wouldn't come off. I thought it was the dried solvent.

I suspect that the solvent reacted with the rain while stacked or something. But if anyone can confirm that, it would be great. I plan on making sure each new sheet is dry and separated from the others.

Thanks in advance..
-Brett
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Re: Aluminum corrosion during storage

Postby ae6black » Fri Jul 07, 2017 11:15 am

I did essentially the same thing. And I got the same results. Also when I tarped my TD the first winter, I got more of the same. You can see where the cord was rubbing against the aluminum when the wind was blowing. What you can do is wet sand with fine sandpaper and then start buffing with finer grade of buffing compound until you get a mirror like finish or you can just live with it. I've tried the acid wash and petroleum jelly with very little success. Mine is a minimal TD and I just got used to looking at it with all of those white and dark blotches all over it. Eventually the color will even out. I know some with this issue have sanded really hard and got a brushed aluminum look that they like. It's really up to you and how much work you want to put into your unit as to what it is going to look like in the end. Personally, I'd just rather use it as is and going camping than get upset over the blotchy look.

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Re: Aluminum corrosion during storage

Postby Andrew Herrick » Fri Jul 07, 2017 8:55 pm

I feel for you. Been there. Expensive lesson to learn!

If you (or anyone else reading this forum) is trying to rescue the aluminum, I think acid washing is the best solution. I think you need fairly strong stuff, though. My research turned Power Clean Acid 2033? Sounds like the stuff is pretty potent.

Anyone have experience with Sharkhide on aluminum? Does that work to prevent corrosion?
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Re: Aluminum corrosion during storage

Postby Andrew Herrick » Fri Jul 07, 2017 8:58 pm

Speaking of Sharkhide ... it seems they also make an aluminum cleaner? You can buy it online, too.
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Re: Aluminum corrosion during storage

Postby brett_x » Sat Jul 08, 2017 6:02 am

ae6black wrote:I did essentially the same thing. And I got the same results. Also when I tarped my TD the first winter, I got more of the same. You can see where the cord was rubbing against the aluminum when the wind was blowing. What you can do is wet sand with fine sandpaper and then start buffing with finer grade of buffing compound until you get a mirror like finish or you can just live with it.


I'm guess I'm glad I'm not the only one. And I'll keep that in mind for the winter storage. I am hoping to not have to tarp it, but I don't know if I'm that brave. We'll see how good I feel about the water-tightness when it's done.

Andrew Herrick wrote:If you (or anyone else reading this forum) is trying to rescue the aluminum, I think acid washing is the best solution. I think you need fairly strong stuff, though. My research turned Power Clean Acid 2033? Sounds like the stuff is pretty potent.


I did try some acid wash - "Aluminex - Pontoon and Hull Cleaner" - on it, and that took care of the crusty white stuff, but still looks terrible. I think sanding would do the trick, but I'm not interested in that level of elbow grease at this point. So I'll use those sheets for some other project in the future- knowing they'll probably just have to be painted.

I picked up some new sheets yesterday and asked the guy that was loading it up. He didn't seem too knowledgeable, but did float the same theory- that the solvent reacted with the rain water, so I do think that's what happened. Here's a picture of one of the new sheets. I had just taken it off my car. Note the solvent patterns. That all dried up within an hour or so.
149437

They had 4 x 10' sheets in stock. My build is 5' wide, so that is much better than the 4 x 8. I won't have a 3x4 cutoff that I don't have much use for. I just have to be careful when cutting because I'll only have about a 1/4 inch of scrap.

Back to the grind.
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Re: Aluminum corrosion during storage

Postby ae6black » Sat Jul 08, 2017 10:16 am

Two aluminum sheets next to each other with water is going to corrode. End of discussion, it's just what happens. I wasn't paying attention and got caught like you did..

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Re: Aluminum corrosion during storage

Postby brett_x » Sun Jul 09, 2017 4:23 am

ae6black wrote:Two aluminum sheets next to each other with water is going to corrode. End of discussion, it's just what happens. I wasn't paying attention and got caught like you did..

Art


Thanks Art. That's good to know. I'll be careful with the new stock... though hopefully I'll have it all installed soon.
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Re: Aluminum corrosion during storage

Postby Tigris99 » Mon Jul 10, 2017 12:09 am

Fine steel wool followed by a buffer.

I wish i could get sheets of aluminum for that price. Spend that per sheet easily out here.

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Re: Aluminum corrosion during storage

Postby Andrew Herrick » Wed Jul 12, 2017 10:58 am

Granted, any aluminum will eventually corrode when trapped with water, but if you can get it, 5052 aluminum is more corrosion resistant (and stronger) than run-of-the-mill 3003 stuff.
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Re: Aluminum corrosion during storage

Postby Wildfire » Thu Jul 27, 2017 12:35 pm

I run an aluminum distribution business... Seen this many, many times in the warehouse.

Classic water staining. Probably from rain, condensation/moist air is just as likely.

The solvent is actually residue from the rolling process. It is "oily" and will protect the metal for a period of time, but time and water win eventually and you get the white stains. Sometimes these sheets have thin sheets of paper between them to prevent scratching - I can't describe how hard it is to get that off once it gets wet and dries.

Typically it can be removed mechanically with scotch brite pads. We use a floor buffer sometimes on the thicker plate. Chemicals have limited effectiveness, Alumabrite is one of the better ones.

Keep water from being trapped next to the aluminum by another sheet, tarp, rope, board, etc. and you'll have the best luck. Best advice, is get it on the trailer fast, don't leave it sitting around.

5052 is more corrosion resistant than 3003, but water staining like this will happen to either pretty easy. My trailer has 5052 on it.

Good luck!
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Re: Aluminum corrosion during storage

Postby brett_x » Thu Jul 27, 2017 1:01 pm

Wildfire wrote:I run an aluminum distribution business... Seen this many, many times in the warehouse.

Classic water staining. Probably from rain, condensation/moist air is just as likely.

The solvent is actually residue from the rolling process. It is "oily" and will protect the metal for a period of time, but time and water win eventually and you get the white stains. Sometimes these sheets have thin sheets of paper between them to prevent scratching - I can't describe how hard it is to get that off once it gets wet and dries.

Typically it can be removed mechanically with scotch brite pads. We use a floor buffer sometimes on the thicker plate. Chemicals have limited effectiveness, Alumabrite is one of the better ones.

Keep water from being trapped next to the aluminum by another sheet, tarp, rope, board, etc. and you'll have the best luck. Best advice, is get it on the trailer fast, don't leave it sitting around.

5052 is more corrosion resistant than 3003, but water staining like this will happen to either pretty easy. My trailer has 5052 on it.

Good luck!


This is SO much help. Thank you. You've answered all of my questions. I did replace the bad stuff, and the new stock is installed. :) It looks great. I'm saving the corroded sheets for other projects. they'll just need a lot of prep work first. I may even be renting a floor sander for something else, and if I do... well, I'll give that a shot with some fine grit.

I did start this project knowing I would learn a ton in the meantime. I've never worked with sheet metal at all before, so this was one of the things I was looking forward to. I even built a metal brake out of a bed frame. Fun stuff. I'm sure this little bit of info will help others who are in the same boat.

Thanks again!
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Re: Aluminum corrosion during storage

Postby beezerboy » Wed Sep 13, 2017 1:18 am

late to the party on this but ya, moisture between the sheets sets off corrosion. another way to clean it is phosphoric acid etch. its common on aircraft.. pro auto paint stores will carry a system like Alodine or Alumaprep. these are 2 part systems with an acid etch and a conversion coat. they are primarily designed to prep alloy for paint. couple ways to use it... do the process and paint as soon as it drys... or if you want the alloy look, skip the conversion coat and buff out the finish after the etch. Scotch Brite and the acid etch will give a flat dull looking surface, but it will be super clean and is fantastic for paint adhesion.
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Re: Aluminum corrosion during storage

Postby brett_x » Wed Sep 13, 2017 5:42 am

beezerboy wrote:late to the party on this but ya, moisture between the sheets sets off corrosion....


Thanks beezerboy. I still have the sheets, and will likely want to do something with them, so I'm still all ears for ideas and this will help. I also posted so that it's here for anyone else that might run into (or need to avoid) issues like this. So thanks again. :)
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Re: Aluminum corrosion during storage

Postby greygoos » Wed Sep 13, 2017 6:58 am

I purchased the aluminum sheets from the same seller as you did at the Syracuse location. I had a similar experience with "corrosion". I used a maroon 3M pad to remove the corrosion then cleaned with wadding. I then used a buffer with compound.
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Re: Aluminum corrosion during storage

Postby aggie79 » Wed Sep 13, 2017 5:14 pm

Not readily available, and admittedly significantly more expensive, aluminum sheeting can be purchased anodized. I purchased my aluminum from a sign company. I don't recall the exact designation, but it was something like "mirror bright" anodized. It has seen plenty of water but looks the same as the day I installed it. I do wax it annually or thereabouts with pure carnauba wax. This isn't for corrosion protection, but is to make it easier to clean tree sap, bird droppings, smashed bugs, etc.
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