ALU skin on galvanized STEEL frame?

[RoadForce]

Well, I have said it before and I will say it again: I have decided on a steel frame with metal sheeting. As the thread title says, I am looking into aluminum sheeting at the moment. I am sure FRP is great for many types of builds and maybe I will use it on some future project, but not now. The FRP ship has sailed, and I intentionally did not buy a ticket. Each to their own, I guess.

So, back to aluminum sheeting on a galvanized steel frame: is 1mm separation of the materials enough to avoid the corrosion issues? I guess so, right? I mean: as long as the two materials are not in contact with eachother, I am OK, right?

 

[ripperj]

I believe corrosion between dissimilar metals occurs due to very small electrical currents, so if the AL is not in contact with Steel you should be ok.

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[oscar the grouch]

The aluminum vs FRP debate can go on forever. Both have their advantages and disadvantages. With either one, internal framing needs to be stout enough to prevent racking should you hit something.


Here in the USA, there's a whole industry built around truck cargo bodies, I'm sure Canada has them to. They come in many shapes, sizes and styles. Morgan cargo bodies are very well built. They have their own engineering team and will supply and ship bodies without a rear door and will supply a single sheet FRP panel to fill in the opening. You can request a build with FRP panels in either 3/8" of 5/8" thicknesses.

Some people think the front leading corners and edges on these bodies are a weakness, but their replaceable, Morgan has a parts catalog for their bodies.

great video. i laughed so many times

 

[RoadForce]

I believe corrosion between dissimilar metals occurs due to very small electrical currents, so if the AL is not in contact with Steel you should be ok.

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So you're saying: no contact = no circuit, so no corrosion? Sounds plausible...

 

[Healeyjet]

Correct, no contact no corrosion. We had the same problem with the 1956 Austin Healey that I rebuilt. The steel frame and the aluminum fenders were a huge problem area. Good primer prior to installation of the fenders and a material to keep the two dissimilar metals separated solves the issue. Should work the same with a steel frame and alu skin on a camper or trailer.
If you care to research further it is called galvanic or bi-metallic corrosion.

Ward

 

[RoadForce]

Thanks. I had already done some searching, but found the commonly used term "in the presence of an electrolyte" a bit confusing (English is not my native language...).

Love (Big) Healeys, btw, great looking cars!

 

[RoadForce]

Got it, thanks!

 

[Iain_U1250]

I am not sure of the shape of what you are trying to cover, but you would just have to be careful anywhere water can pool - that will create the electrolytic contact needed for corrosion. Do 3M recommend any protection of the steel - The Sikaflex people said I had to paint my steel and use their primer to create a good bond. What are you going to use for caulking - silicone? Are you planning on painting the aluminium?

 

[veetee]

I would not use silicone for caulking, because there is some acetic in silicone caulking, which is not good with respect to corrosion. I'd rather use Sikaflex or Innotec caulking.

 

[rayra]

A good epoxy paint or powder-coating of the frame before attaching the aluminum will pretty much solve the issue of galvanic corrosion.
That or apply some strips of butyl-rubber peel and stick window flashing to the framing where the aluminum panels will otherwise be in contact.

 

[lost1]

I also used aluminum sheet over a steel frame for my unimog camper. I ran beads of sikkaflex on the metal frame and embedded spacers that were made of weed eater plastic string every few inches. Once I glued the aluminum to the steel I used my continuity tester to verify that there was no circuit (contact) between the aluminum and steel. There is an optimal depth of bead for the sikkaflex and I found that the weed eater string worked well to keep this depth.

 

[mog]

I also used aluminum sheet over a steel frame for my unimog camper. I ran beads of sikkaflex on the metal frame and embedded spacers that were made of weed eater plastic string every few inches. Once I glued the aluminum to the steel I used my continuity tester to verify that there was no circuit (contact) between the aluminum and steel. There is an optimal depth of bead for the sikkaflex and I found that the weed eater string worked well to keep this depth.

Great tip on the weedeater string for a spacers. Thanks

 

[calstar]

aluminum and galvanization

Interesting thread. Heres a site with basic info regarding aluminum and galvanized steel:

http://www.galvanizeit.org/hot-dip-galvanizing/how-long-does-hdg-last/in-contact-with-other-metals

Let us know how your build goes RoadForce The 11"8" vid is a crackup, especially the two hay haulers, first one hits and unbelievably the second one does the same!! Its not like there isi no signage, flashing yellows and all don't make a difference for those poor folks.

Brian

 

[Nhdoucette]

I also used aluminum sheet over a steel frame for my unimog camper. I ran beads of sikkaflex on the metal frame and embedded spacers that were made of weed eater plastic string every few inches. Once I glued the aluminum to the steel I used my continuity tester to verify that there was no circuit (contact) between the aluminum and steel. There is an optimal depth of bead for the sikkaflex and I found that the weed eater string worked well to keep this depth.

When you put the aluminum skin on did you overlap the sheets or just butt up them against each other?

 

[lost1]

I overlapped the sheets by a few inches. The thought of trying to butt large sheets of aluminum and have them fit nicely would have been a challenge to say the least. I often work alone