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Old 11-01-2015, 10:19 AM   #1
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Does spray foam cause rust?

I'm a bit confused. My plan is to pull down the ceiling panels, remove insulation, remove any rust, and put new insulation in. I don't know what kind of insulation yet, but I was planning on "filling gaps" with spray foam.

I came across this post where it appears the spray foam caused the rust. Is spray foam a bad idea? Are there certain types that are okay to use and some that are not?



http://www.skoolie.net/forums/f9/is-...bus-12263.html
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Old 11-01-2015, 11:08 AM   #2
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The guy in that thread never confirmed what type of foam it was.

From my research, closed cell spray foam is actually water proof, dries hard, and to a certain degree becomes structurally beneficial.

Open cell spray foam is more like a sponge. It is porous, absorbs water, and is squishy. Open cell is cheaper, but not good for a bus. I bet that was open cell foam on that bus.

So assuming we disregard open cell foam altogether and focus on closed cell, that does bring up a good topic of discussion: are there certain brands/types of closed cell spray foam to avoid? Most of these foams are probably meant for wooden residential applications and might have a bad reaction to metal?
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Old 11-01-2015, 11:27 AM   #3
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Everything Tippyman said is true.

Then their are one part spray foams like great stuff. The chemicals they are made from are corrosive to metal if not cured perfectly.

Great stuff should not be used in a bus. If I was at the beginning of my build, I would not have sprayed the stuff into everyone of my support ribs.

Two part closed cell spray foam sprayed at the proper temp with full bond to the bus metal should never cause a issue.

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Old 11-01-2015, 11:54 AM   #4
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I did my research on this long ago and this is a clip of some advice from a pro.

NOT my words, or my opinion but those of an expert. YMMV.

"Combining foam and metal roofing
The challenge comes when you combine systems, spraying foam onto the metal roofing itself. Metal roofing manufacturers typically extend a 25-year warranty. The concern of manufacturer MBCI is over who is going to verify that the foam will not cause corrosive damage over time to the roofing.
Most foam companies are not willing to provide written guarantees that their product will not cause problems and that they will stand behind any damage that may happen.
Most roofing companies will void or waive their warranty under these circumstances."
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Old 11-01-2015, 11:56 AM   #5
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So people have used closed cell foam on buses with no problems causing rust.

What does the "one or two part" refer to? Like its made of two things and as you spray it, it mixes together?

Where do you get spray foam? Are there some made for metal?

I am curious to find out about
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Old 11-01-2015, 12:03 PM   #6
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Yes, one part is a single chemical that needs air to cure.

Two part uses two chemicals and needs no air to cure.

Commercial roofs are sprayed with a closed cell 6 pound two part foam everyday with no long term issues. The video's are all over the net.



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Old 11-01-2015, 02:45 PM   #7
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Just read this on the FAQ page for a company local to me:

FAQs - Spray Foam | Insulation Products | Polyurethane Foam

Is spray Polyurethane foam insulation corrosive to metals?

No, spray Polyurethane foam insulation is non-corrosive.
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Old 11-01-2015, 03:34 PM   #8
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Quote:
Originally Posted by 2kool4skool View Post
I did my research on this long ago and this is a clip of some advice from a pro.

NOT my words, or my opinion but those of an expert. YMMV.

"Combining foam and metal roofing
The challenge comes when you combine systems, spraying foam onto the metal roofing itself. Metal roofing manufacturers typically extend a 25-year warranty. The concern of manufacturer MBCI is over who is going to verify that the foam will not cause corrosive damage over time to the roofing.
Most foam companies are not willing to provide written guarantees that their product will not cause problems and that they will stand behind any damage that may happen.
Most roofing companies will void or waive their warranty under these circumstances."
25 years huh? Think it's worth trying to contact the company who insulated my bus and try to get the roof replaced? I bought it from a church who bought it from another person/group who bought it from Champion. I guess I should probably call Champion and see what the deal with that is yeah?
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Old 11-01-2015, 03:45 PM   #9
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You can buy poly boards that are cured. A little bit of carving (on the inside of the board ) to make the curve and pushed up tight are cheaper but they are cheaper because you have to form them. Cheaper, a little effort and you get a better product and with a commercial supplier if you tell them the curve then you pay a little more but your pieces fit where you want them. I build commercial tanks for a living. I use poly on everything from chilled water 25-30* to steam 150-200*? The only thing that changes is the thickness. 1-1/2" takes care of most chilled and up to 100* steam and then we change to 2" thick. Go to KNAUF insulation website and research polyiso insulation or BOATWRIGHT.
They are made to order!
If I had to figure my bus roof for this? I would figure a 7' diameter tank at 9' tall. Because I am not wrapping a tank I am only doing the roof so the extra 3/4 should be enough. Sorry I am not a math nerd but I do know how to keep up with my insulation subs and question there quotes?
Sorry didn't mean to put y'all in my world but there are options to the spray foam world? This has started happening in commercial construction in the last 5-years and it is a good green building thing but they are not using it on metal and the off gassing has yet to be determined? The option I suggested is probably cheaper and doable by the owner.
I have demoed steel tanks and steam piping in underground flooded tunnels that were 50-60 years old with the polyiso insulation and the paint was still on the steel. It was a little rusty but the inside of the equipment was past its life and the insulation had not effected the steel?
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Old 11-01-2015, 04:52 PM   #10
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Putting rigid formed foam panels inside your roof will still allow condensation to form on the inside of the outer metal skin.

Properly sprayed foam, onto a clean properly prepped surface will not allow any condensation to form.

It's all about moving, or transferring the due point.

I want the due point on the inside living space surface (finished walls and ceiling), not inside my walls / ceiling.

No cavity or spaces is best.

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