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Avoiding RV electrolysis damage

A discussion started in 2002 but continuing through 2019


Q. Hello,

I don't know if this question has an answer. I recently had extensive work done on the aluminum siding of my RV trailer. I was told that this damage was done by electrolysis. we use our unit a lot in the winter and of course road salt seems to have taken it toll. My question is can this be prevented in any way? Would the zinc blocks help?


Lloyd W [last name deleted for privacy by Editor]
- Mission, British Columbia, Canada

affil. link
Rust Converter


A. I'm afraid that zinc blocks would probably be close to useless, Lloyd; for them to do anything you need a conductive ionic path. That is, two routes for electricity, one through the metal, one through the water. If your RV was covered in salt and thoroughly drenched with water, they might work a little during that period. What you probably need is proper surface preparation before repainting. Look for a "rust converter" or similar phosphoric acid like treatment. Good luck.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

April 14, 2013

Q. How do I correct the problem of electrolysis on my motorhome now it's like cancer?

Angela Wright
- Cave Juction, Oregon, USA

April 16, 2013

A. Angela,
Any fix is going to require a good deal of effort. You need to sand down the rusted areas, prime, then paint. If you have severe corrosion (rust holes) seek out a body shop.

Marc Banks
Blacksmith - Boone, North Carolina, USA

May 16, 2019

Q. Rust is an oxidation product of iron. Steel rusts, too, because of the iron in it. Aluminum electrolysis is not an iron driven reaction, is it? Do phosphoric acid rust reducers work effectively against aluminum?

- BURLINGTON, Washington

May 2019

A. Hi Michael. Chromate conversion coating is a more effective pretreatment for aluminum than phosphatizing, but it can be an environmental issue (hexavalent chrome) and it's probably not very practical for an RV owner to do their self. It's probably true that a phosphoric acid based rust converter doesn't really do very much chemically for aluminum, but it probably can assist a little with etching for better adhesion of the primer.

None of this has much to do with battling galvanic corrosion ('electrolysis' isn't quite the right word), except that painting stuff offers some corrosion resistance and aesthetic benefit :-)


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Ted Mooney, P.E. RET
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finishing.com - Pine Beach, New Jersey

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