Tent Trailer Metalurgy

"Rusty Vandura - www.tinyurl.com/keepoppo" (rustyvandura) 06/23/2020 at 13:34 • Filed to: None

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The aluminum skin in the roof of my tent trailer is literally rotting from the inside. I don’t know what to make of it. So I’m patching it. So far, it’s only showing up on the front. Have any of y’all seen anything like this?

farscythe - makin da cawfee! > Rusty Vandura - www.tinyurl.com/keepoppo 06/23/2020 at 13:40

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i have seen it before...but i couldnt tell you what it is exactly

saw it a lot on ratty old caravans back when i worked that job

seems to be something that likes to happen to that wierd stamped luminum paper mache stuff

Sovande > Rusty Vandura - www.tinyurl.com/keepoppo 06/23/2020 at 13:48

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Electrolysis from dissimilar metals ? What is the substrate? Steel framing? My guess is that moisture is somehow getting in and causing the problem - find the source of the moisture and seal it up.

Highlander-Datsuns are Forever > Rusty Vandura - www.tinyurl.com/keepoppo 06/23/2020 at 13:55

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It’s just the aluminum oxidizing at the joint. Aluminum does oxidize but usually the member is thicker so there is little loss of strength. It also appears that there is maybe stainless steel under the aluminum skin? That would make the aluminum cathodic to the steel. There should be a coating between the SS and the AL. 

Rusty Vandura - www.tinyurl.com/keepoppo > Highlander-Datsuns are Forever 06/23/2020 at 14:06

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There’s nothing directly under the skin between it and the styrofoam insulation. There’s no joint except in the insulation. The oxidation just blistered and then popped over a period of years.

Rusty Vandura - www.tinyurl.com/keepoppo > farscythe - makin da cawfee! 06/23/2020 at 14:07

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Interesting. Hopefully this patch will buy me some more years.

Rusty Vandura - www.tinyurl.com/keepoppo > Sovande 06/23/2020 at 14:08

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I wondered about moisture being the culprit. I also thought that aluminum was supposed to be impervious to moisture.

farscythe - makin da cawfee! > Rusty Vandura - www.tinyurl.com/keepoppo 06/23/2020 at 14:10

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the patch will *probably* fix any leakage....but i dont think itll stop the rot

but you’ll need someone with more expertise than me to fix that

old caravan metal is strange stuff

ttyymmnn > Rusty Vandura - www.tinyurl.com/keepoppo 06/23/2020 at 14:15

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Looks like my back screen door. Looks like aluminum over some kind of paperboard. Or maybe not aluminum at all. Maybe just the frame is aluminum.

Rusty Vandura - www.tinyurl.com/keepoppo > farscythe - makin da cawfee! 06/23/2020 at 14:17

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I do not expect the patch to stop the aluminum from rotting. I am fairly confident that the patch will stop the leaking.

Sovande > Rusty Vandura - www.tinyurl.com/keepoppo 06/23/2020 at 14:17

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The water could be getting in anywhere and migrating to the places where it is showing bubbling. The insulation could be the culprit by holding moisture.

Rusty Vandura - www.tinyurl.com/keepoppo > Sovande 06/23/2020 at 14:25

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I’d thought of that.

Rusty Vandura - www.tinyurl.com/keepoppo > ttyymmnn 06/23/2020 at 14:25

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That’s very attractive.

MasterMario - Keeper of the V8s > Sovande 06/23/2020 at 14:41

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The framing on these are generally wood. 

Sovande > MasterMario - Keeper of the V8s 06/23/2020 at 14:50

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I know nothing about it, just trying to equate to electrolysis in boats that is generally caused by stray current in the water at marinas and the reason that boats use sacrificial zinc/magnesium anodes are used at locations such as the running gear and internal engine components. Maybe it is similar with the moisture that is trapped in the insulation? Are trailers grounded when powered up? Could current running through the skin and moist insulation be causing this?

Or maybe just old?

Rusty Vandura - www.tinyurl.com/keepoppo > Sovande 06/23/2020 at 14:51

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In the absence of moisture, would the rot continue to advance? Is it adventageous to trim the rotting parts?

MasterMario - Keeper of the V8s > Sovande 06/23/2020 at 14:57

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I’m thinking just old and moisture in the wood behind it. The trailer itself looks like it’s about 20+ years old.

I don’t know enough about electricity to say whether that’s a factor here. They generally have a house battery as well as a cable to plug into a dedicate circuit (like a boat would with shore power).

Sovande > Rusty Vandura - www.tinyurl.com/keepoppo 06/23/2020 at 14:58

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I have no idea, frankly. My experience is very specifically limited to boats. I used to run a large aluminum landing craft and every modification had to take electrolysis taken into account. Steel bolts were coated with something and in places where steel cleats and things were attached to the aluminum we had to use rubber gaskets. I also worked on a small tug that had an A Frame on the bow for lifting large anchors onto the deck. It was a steel boat and we used aluminum diamond plate to keep the deck from being scarred up. The plate would last about a year before the aluminum started to disintegrate around the bolt holes. By that time the diamond plate was basically worn smooth so it was not a big deal anyway.

I would think the skin is likely very thin and likely not a high-grade aluminum to begin with wh ich could be the problem. It’s possible it has a viable life span that is nearing its conclusion.

CalzoneGolem > Rusty Vandura - www.tinyurl.com/keepoppo 06/23/2020 at 15:10

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Oh my you’re fancy!

I probably would have used a license plate.

Thisismydisplayname > Rusty Vandura - www.tinyurl.com/keepoppo 06/23/2020 at 15:53

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Could be a galvanized steel skin.  It’s likely over wood of some sort.  We had a pop up that had roof damage and the underlay wood was pretty trashed.  Lots of silicone sealant and eventually a coating of mobile home roof paint mostly fixed it.  We would just have to push the roof up after a rainstorm to empty the sagging puddle.  

Rusty Vandura - www.tinyurl.com/keepoppo > Thisismydisplayname 06/23/2020 at 16:31

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That’s an interesting idea; it could be galvanized steel, but I don’t think it is because it’s very malleable.

Rusty Vandura - www.tinyurl.com/keepoppo > Thisismydisplayname 06/23/2020 at 20:44

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You called it. That’s exactly what it is and exactly what’s going on. Moisture trapped behind galvanized steel.

Thisismydisplayname > Rusty Vandura - www.tinyurl.com/keepoppo 06/23/2020 at 22:21

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The patches should do the trick though. You likely have a leak from the roof somewhere though. Possibly some flowable silicone could  take care of it.