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Old 09-05-2013, 08:54 AM   #1
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1977 23' Safari
Niagara on the Lake , Ontario
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Stopping Electrolysis

I'm in the middle of making some repairs to the bathroom and rear frame of my Airstream and have had a major problem with corrosion on the filler panel between the trunk box and the frame/rear hold down plate.

What is everyone using to prevent future corrosion between the dissimilar metals?

I am having a new hold down plate made, and I will be picking up aluminum for a new filler panel and don't want to have this corrosion happen again, even if it is another 35 years.

I read on an offroad forum that some people use clear packing tape to insulate the metals from one another. Any other suggestions?

1977 Safari Land Yacht
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Old 09-05-2013, 09:15 AM   #2
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1994 31' Legacy 30
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Junction of dissimilar metals

I'm not sure you can stop this type of corrosion but you can slow it down. Seal the area so that little or no moisture can get to it. Prime the steel parts with a zinc rich primer and coat the aluminum parts with clear polyurethane. Use stainless steel fasteners. And make an effort to insure that the shell and frame are well connected (grounded) to each other so that there is no current flow between the two.

Good luck with your project,

Tony T
2000 28' Classic TT
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Old 09-05-2013, 10:02 AM   #3
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Dissimilar (not the same) metals in contact with each other, with no electrical activity between them, should not accelerate corrosion... All covered somewhere in this vast knowledge and experience forum.

Here is some "light" reading...
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Old 09-05-2013, 11:29 AM   #4
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1981 31' Excella II
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Keep edges and seams coated with wax or oil to insulate and stop corrosion. If you keep water from getting in between cracks you can stop corrosion. WD40 applied often will work. Paint parts to provide electrical insulation. Two metals in direct contact in water = Corrosion. Even putting an insulator between the two metals will help.

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Old 09-06-2013, 07:49 AM   #5
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Thanks for the replies, after some further reading online I thing the more appropriate term is Galvanic Corrosion.

Once the trailer is put back together there is no access to the Hold down plate as it is covered by the outside and inside skins. The hold down plate is steel sandwiched between the aluminum skin and the aluminum C channel. There is also an aluminum filler panel which is sandwiched between the hold down plate and the steel rear frame cross member.

Since the trailer moves I worry that most coatings will rub off over time, leaving aluminum in contact with steel.

Mustang restorer's often use Truck bed-liner to coat items that rub such as the fuel tank straps and the underside of the trunk pan which contacts the top of the fuel tank. I may use this on the hold down plate, and apply a coat of POR15 to the inside of the aluminum skin and C channel to insulate the metals from each other. Hopefully a spot of Tempro on the rivets will be enough to insulate the aluminum rivets from the steel plate and keep water out. Once the plate is installed, before I re-install the inner skin, I may spray the area with RustCheck rust proofing oil to try and keep moisture off.

My concerns are probably unwarranted since the trailer survived for 36 years without any of this.
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