TheRealPapaK
Active member
If you use closed cell foam, that will stop the corrosion issues correct?
Rust protection inside the frame, idea
- Thread starter high-and-dry
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high-and-dry
Active member
No, its a temp differential and condensation issue, moisture will get in and sit against the metal. unless you can 100% make sure its air tight it will cause rust.
TheRealPapaK
Active member
So if I have a van wall and I spray closed cell foam against the wall I can still get corrosion between the wall panel and the closed cell foam? Wouldn’t that be airtight? I realize the OP had a different question but I just want to make sure I’m not going to cause myself an issue
ducktapeguy
Adventurer
In a perfect world the seal would be perfect and no air/water would penetrate, and no rust will form. That will never happen in the real world. I can‘t even get some of my cars to stop leaking oil from between two machined surfaces with a gasket, there is no chance spray foam on sheet metal will stay air or water tight for any length of time. It may work for 90% of the surface, but you won’t know which ones until it’s rusted through.
This is the result of spray foam insulation on the interior sheet metal. The problem is the foam isnt waterproof enough to block out all moisture, but just waterproof enough not to let it out once it’s in there. It may work for a desert car that doesn’t see much humidity, but in the long run there will be problems
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high-and-dry
Active member
The foam will over time separate ever so slightly as the metal expands and contracts from the sun hitting it. That will also cause air to get in to the gap and that air will have moisture, the moisture will condense on the cooler surface and not be able to get out as easily. If you have a good coating or any zinc plating be it galv or just a electroplating it maybe ok.
There is also a huge difference on modern car bodies even the inside for coating vs raw steel we build our frames out of.
TheRealPapaK
Active member
Sorry for hijacking the thread. So basically I am converting an ambulance right now. It's all aluminum 2" studs with aluminum exterior panels. Right now they have 1" rigid poly iso and then aluminum bubble insulation that is taped to the studs as a vapour barrier. I was pretty concerned about the vapour barrier being there because I though moisture could get trapped between that and the aluminum wall. But as I pulled some of it back, it seems fine. Now I'm at the point of wanting to stop the thermal bridging of the aluminum studs. Alls added up, there is almost 32sq/ft of thermal bridging on the aluminum studs. I was thinking of pulling off all the foil bubble insulation and spray foaming on top of the existing 1" polyiso board to fill the remaining wall cavity and covering the studs with 1/2" or 3/4" of spray foam. Do you think this is a bad idea? the other option is just put foam furring strips on the studs but I wanted to beef up the insulation in the walls anyway because we will use this for skiing etc.
opp
Observer
As we build trailtop trailers glass over foam fond sheets are 50% cheaper and stronger not fighting to get a flat spot back fill with can foam
high-and-dry
Active member
I have no doubt c channel is strong enough if it is sized properly. But I think it will rust too, if its steel it will rust. my issue is dirt and mud can easily get on the bottom flange and hold water against the metal
What I have decided to do at the point is I am going to fluid film the inside of the frame and I have already done the frame coating. So I will have both helping to prevent and or stop the rust. I am a firm believer in the fluid film. I am going to leave the holes open.
opp
Observer
The thing with the c channel is you can put yes on it . When I was a kid they make docks with drums filled with foam and covered with oil tar seem to hold up for 20 years are more . I see where foam not under pressure would fall a part
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high-and-dry
''I am a firm believer in the fluid film. I am going to leave the holes open.''
What would stop it from drying out from dust ,mud that get in to the holes. Rust may be like none of us are get out of here alive but you can do things to prolong
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high-and-dry
''I am a firm believer in the fluid film. I am going to leave the holes open.''
What would stop it from drying out from dust ,mud that get in to the holes. Rust may be like none of us are get out of here alive but you can do things to prolong
DaveInDenver
Middle Income Semi-Redneck
Fluid film doesn't dry but it does attract dust to make an oily goop on the surface. That seems fine on my truck since the surface next to the steel is still a waxy oil just with debris in it. The stuff does wash off eventually with any water so Fluid Film isn't a one-and-done anti-corrosion but maintenance you do periodically.
I prefer 'C' channel over a boxed or use profile in this case. You can never really protect the inside of a tube unless you dip the whole assembly and especially if you weld to it you burn off any paint or protection inside you may already have. But it's doable if you put enough weep holes large enough to fit a wand inside.
I prefer 'C' channel over a boxed or use profile in this case. You can never really protect the inside of a tube unless you dip the whole assembly and especially if you weld to it you burn off any paint or protection inside you may already have. But it's doable if you put enough weep holes large enough to fit a wand inside.
high-and-dry
Active member
I figure inside the frame it wont really wash off, and I drilled holes every 3 feet or so to do the eastwood coating.