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Author Topic: differant types of metal fastened together  (Read 2364 times)
happycamperbrat
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« Reply #15 on: April 19, 2011, 12:32:42 PM »


I would not put aluminum and steel together in an outdoor application.

We had our steel roof replaced with an aluminum one early on in the conversion process.  We used butyl rubber tape on all the trusses before the skin went down, and butyl-sealed rivets throughout so there is no metal-to-metal contact.


-Sean
http;//OurOdyssey.BlogSpot.com


So Im assuming an indoor application would be okay? Also, what would be the lifespan of those rubber tape fasteners outside?

I have steel bulkheads and need to make bay floors. Right now Im exploring my options for doing the floors. I happen to have tons of al that I pulled out of the inside of the bus and would love to reuse.....
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The Little GTO is a 102" wide and 40' long 1983 GMC RTS II and my name is Teresa in case I forgot to sign my post
bevans6
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« Reply #16 on: April 19, 2011, 12:49:29 PM »

If I recall an earlier conversation correctly your RTS is stainless below the belt line.  That is about what I was suggesting as a bad idea - riveting aluminium to stainless as a structure (a floor is a structure) on the bottom of a bus  Grin

I believe Sean used the rubber tape as an insulating layer, probably with some structural capability but the sealed rivets  would be the actual fasteners/loaded fasteners.  Some tractor trailers are put together with ultra strong double sided tape, so using tape to make things can actually work very well.

If I were making bay floors I would probably match the material to what was there previously.  But you can use aluminium if you do it right, the bay floors on my MCI are aluminium.  I never stopped to consider that until right now, to be honest, since the framing is steel on the interior bulkheads and stainless steel on the exterior tube frame structure down there.

Brian
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happycamperbrat
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« Reply #17 on: April 19, 2011, 02:41:08 PM »

Brian, sadly mine was one of the ones made with mild steel at the bottom. Above floor level I have all stainless, but not below  Cry I got rust behind my wheels to prove it too  Cry
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Sean
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« Reply #18 on: April 20, 2011, 09:46:30 AM »

So Im assuming an indoor application would be okay?


Well, let's say it is less of an issue.  This type of corrosion is facilitated by the dissimilar metals being in an electrolyte solution, and is further exacerbated by anything that "completes the circuit."  Salt water is an excellent electrolyte, which is why you hear about this problem constantly with coastal boats.  However pretty much any water, such as rain water or road spray, will pick up enough minerals to be at least a weak or mild electrolyte, and that's when dissimilar metal contact will begin to corrode.

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Also, what would be the lifespan of those rubber tape fasteners outside?


The tape is not a fastener, and is only sticky on one side.  It is strictly a dielectric (insulator) to separate the dissimilar metals.  The fasteners are the rivets.  In order for the rivets themselves not to be the element that completes the circuit (and themselves subject to galvanic corrosion), a butyl-insulated rivet is used.  The butyl keeps the rivet head away from the skin and also seals the hole so that no water can ingress.

The tape should last as long as the joint is in place.  However if the panels ever need to be separated I would replace the tape with fresh.

-Sean
http://OurOdyssey.BlogSpot.com
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happycamperbrat
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« Reply #19 on: April 20, 2011, 10:02:06 AM »

Thanks!
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