decisions decisions

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decisions decisions

Postby QueticoBill » Tue Aug 15, 2017 3:20 pm

This is where I'm terrible - hate to make a choice without exhausting all the possibilities.

I think there is consensus that 1/8" - or 3 mm - baltic birch is probably fine for interior walls and roof, and maybe not so overwhelmingly the top of roof. I'm thinking about it for exterior of walls, but with fiberglass and epoxy. (is that rmf instead of pmf - rich mans fiberglass?) 1/8" ply skins would sandwich 1" XPS so a pretty solid panel. It just seems the fiberglass would make up for the less strong 1/8" as compared to 1/4" ply I was planning - and save more than the fiberglass I was not planning.

I could revert to ultraply and pmf - as I said - I have trouble just "going for it". And if I went to the 1/8" baltic birch, then I have to revisit the idea of making it taller since the 5x5 panels makes that no cost.........
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Re: decisions decisions

Postby tony.latham » Wed Aug 30, 2017 9:28 pm

I think there is consensus that 1/8" - or 3 mm - baltic birch is probably fine for interior walls and roof, and maybe not so overwhelmingly the top of roof.


I build my tops from 1/8" BB in the ceiling, hard foam, and 1/8" on top. Super strong.

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Tony :thumbsup:
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Re: decisions decisions

Postby QueticoBill » Thu Aug 31, 2017 3:04 pm

But you don't really use the foam for structure do you? I'm on edge of 1/8" bb for top. Thinking underlayment ply for walks, seal/reinforce wall top joint with fiberglass tape and epoxy, and pmf roof if not whole trailer. Cant decide - get consensus - on interior finish.

Thanks for support.
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Re: decisions decisions

Postby dancam » Fri Sep 01, 2017 2:45 pm

QueticoBill wrote:But you don't really use the foam for structure do you? I'm on edge of 1/8" bb for top. Thinking underlayment ply for walks, seal/reinforce wall top joint with fiberglass tape and epoxy, and pmf roof if not whole trailer. Cant decide - get consensus - on interior finish.

Thanks for support.

Yes, foam is used for structural parts. There are large foamies that have no wood or metal above the trailer deck iirc.
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1/8 plywood over foam should be plenty strong for a roof even if you want to walk on it. Make a test piece. Buy some plywood and foam and make a panel and see what you think. Some of us are doing it with foam and canvass, thats it. Seems to work.
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Re: decisions decisions

Postby QueticoBill » Fri Sep 01, 2017 3:32 pm

I wasn't clear. I do plan to use just foam and ply and no ribs. It just seemed like in the photo the ribs and strapping were proud of the foam so it could not be well adhered to play. From my other experiences with foam core and stressed skins for 40 years I've found the differences in how the framing, skin, and foam react to temperature and humidity make the framing almost undesirable.

I've been playing with the idea of fiberglass tape over the joint in the roof - just one with 5 x 5 - before laying it up on walls. Just seems like it might lay much smoother.

PS: Here's an example of my designs. http://nebula.wsimg.com/5aacabca03d55d7 ... oworigin=1 All of the clouds are foam core panels with 3/6" hardboard skins and no frames - two hangers at ends of 4 x 8s - and installers walked on then 40' in the air.
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Re: decisions decisions

Postby dancam » Fri Sep 01, 2017 3:58 pm

I did misunderstand you, thought you were questioning building with foam
With the photo tony posted it looks like the verticle strapping is just to temporarily clamp the foam to the interior bb, the photo is too pixled for me to see if its proud or recessed, but anyway. Since you know all about foam, what would be the reason 1/8th over foam wouldnt be strong enough? How big is the roof? What loads are you seeing on there? I mean if youve built foam sandwich panels with (3/16?) Wood that people can walk on 40ft in the air why wouldnt that be good enough for a trailer?
Why go with 1inch foam and 1/4in wood instead of 1.5in foam and 1/8th wood?

I just discovered the humidity thing with my first foamie here.... did frameing and canvass over the foam and you can see exactly where the wood is every evening because its soaked with condensation... :/

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Re: decisions decisions

Postby QueticoBill » Fri Sep 01, 2017 7:43 pm

I need to work on my writing. Planning 1 1/2" foam and 1/8" bb for top and hatch, ribs at crosswise edges only. Its the walls I was considering 1/8 instead of 1/4 bb for. And how that affects finish or skin. I'm leaning to just a coating on walls- no glass or canvas.
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Re: decisions decisions

Postby tony.latham » Fri Sep 01, 2017 7:46 pm

But you don't really use the foam for structure do you?


It's primary purpose is for insulation, but it does add a lot of strength––just like a SIP:

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I do the hatch the same way. Adds a couple pounds of weight but really stiffens it up. :thumbsup:

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