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Old 08-17-2004, 03:06 PM   #1
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Aluminum exfoliation

The floor channel on my '59 Tradewind has a bad case of corrosion, especially around the steel bolts that hold the channel to the floor.

I believe it is called exfoliation.

I can remove the white residue with scotch bright and mineral spirits, but what do I do after that? Are chromate paints the answer? How about neoprene washers and stainless steel bolts? Anyone with an idea please pipe up.

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Old 08-17-2004, 06:12 PM   #2
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stainless bolts sound like a good idea, the neoprene washers can't hurt either!


you call them ferrets, i call them weasels.
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Old 08-17-2004, 06:34 PM   #3
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I plan on SS bolts with BIG aluminum washers (read flat stock) I had considered using SS washers but was worried about the wear issues.

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Old 08-17-2004, 08:12 PM   #4
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Exfoliation looks like a french pastry(a mille feuilles).On these parts it is just severe surface corrosion.My fix was to replace all the "U" channels.To salvage lightly corroded chanels paint with zinc chromate primer.Again I say do not use stainless with 2024 aluminum.It works with 5000 series boat aluminum but rots 2024.Use the cheaper zinc plated steel.
When I worked on the DC10s stainless screws put in panels a year earlier had to be drilled out and left behind pitting in and around screw holes.Plated steelscrews always came out easy and did no damage.
A little rust inhibiter like LPS3 on "U" channels wouldn't hurt either.
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Old 08-18-2004, 08:02 AM   #5
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I have a related question. A long time ago, there was a battery leak in the front-mounted battery box. There doesn't seem to be terrible damage to the skin of the trailer, except to one spot in the belly pan, which I plan to patch up anyways. However, there is a slight (superficial) whitening of the surface of the skin where the drips went, though nothing that looks awful. By no means does it look like french puff pastry, more like a very thin veneer of dried up snot (and regarded by me just about as favorably as snot).

My question--has anyone encountered this kind of skin damage in polishing? I'm hoping to move on to polishing next year, but never considered if this would present a problem. I've supposed that I would just remove that layer and polish the good aluminum underneath--should I try?

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Old 08-18-2004, 08:16 AM   #6
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I had this problem so bad I have to have a metal shop make me 8 ft of new u-channel. Where I salvaged the u-channel that had this problem I sanded or quick once over with the sand blaster and then painted it with some aluminum hull paint I bought at West. There was some of this corrosion on the inside of the body from chemical reaction from leaking head and from a electrical problem (yeah the PO managed to have an electrical fire). Hand sanded and painted it as well to seal it up. So far so good. My lower panels are not in yet so I can still see these areas and it seems to work.

I also went back with the Zinc plated hardware. I had asked a simular question about the stainless about a year ago and got cautioned against possible issues with the dissimular metals.

Now against advice I took all them rusty steel screws out of the rub rail and went stainless but I am keeping an eye on them and I sealed them with Vulkem. I periodicly will remove one and see if I am having problems. Sealing them I think will help because most corrosion needs the O2 to happen.
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Old 08-18-2004, 08:54 AM   #7
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I plan to salvage about half of the floor channel. Thanks for the zinc chromate recommendation.
The side panel I am going to replace is 40" high. The aluminum sheet I bought to replace it is 48" high.
Voila! (another french term), I split the 8" piece in half and have enough 4" strip for 24 ft of floor channel.

Would it be a good idea to paint the lower inside edge of the skin panels too? Where they meet the floor channel. Or would just the Sikaflex be good enough.
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Old 08-18-2004, 09:32 AM   #8
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Originally Posted by 59toaster
... I had asked a simular question about the stainless about a year ago and got cautioned against possible issues with the dissimilar metals.

...Sealing them I think will help because most corrosion needs the O2 to happen.
Actually, water is the primary ingredient in dissimilar metal corrosion. Sealing is a great backup plan, but keeping seams sealed, etc. to guard against water getting to the fasteners is the best first line of defense.

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Old 08-18-2004, 10:54 AM   #9
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A couple of other factors:
1. sacrificial anode (the 'zinc' in zinc chromate, or galvanized screws)
2. exposed surface area. A large anode and a small cathode (steel screws in aluminum channel) will corrode more slowly than a large cathode and small anode (aluminum rivets in a steel frame)

I noticed that in totally dry areas, I had no corrosion of steel screws against the aluminum channel after 45 years. In wet areas, the channel was corroded through.

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