question about foam

Canvas covered foamies (Thrifty Alternatives...)

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Re: About the types of foam...

Postby mdk » Sat Mar 10, 2012 7:24 pm

Is any of it stronger than any other?
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Re: About the types of foam...

Postby KCStudly » Sat Mar 10, 2012 8:16 pm

I believe it pulls off fairly easily, but I only have experience with that on small pieces; have not attempted to do a full sheet. I think Mike (10' Standie Foamie) and GPW (the godfather of the modern Foamie movement and foam RC airplane enthusiast) have had success with either method.

There are different grades or densities of XPS, some are intended to be used under gravel base and/or concrete floors (I believe Foamular 300...?) and others for wall insulation (Foamular 150...?), or just sound deadening. There may be some minor differences in strength, but I would not worry about that too much. The real strength is in what thickness foam and what skin material you use. Assuming you achieve a solid bond between skin and foam, the thicker you make the foam the stronger/stiffer your panel will be. The more robust you make your skin the more puncture resistant (i.e. 1/8 or 1/4 inch ply exterior might resist branches or frozen turkeys better than bed sheet or canvas and glue, or even fiberglass/epoxy). For this reason, I think the lower density/lighter versions of foam are preferred. The foam is not the strength. How far apart the skins are has much more effect on strength (the moment of inertia, I^4, goes up when the outer fibers of the stressed member are further apart).

I haven't built my cabin yet so I am mostly just sharing what I have read here, but it does make sense to me.

A lot of the nitty gritty info is deep within the "Big Thrifty Thread". As daunting as it seems, you may want to read the first 175 to 200 pages :thinking: :oops: :roll: :thinking: ...sort of a right of passage thing for "Foamlings".

There have been some contrary opinions or later developments (such as the postulation that "the mixture" of polyurethane and thinner could cause a breakdown of the glues in modern plywood), so you still need to make some decisions or do some testing for yourself, but the bottom line, IMO, is that most of the techniques and materials used here will give reasonable results proportional to your care in construction, application, and post construction maintenance.

My details are all from memory, so anyone feel free to jump in and correct, or amend anything I have written. 8)
Last edited by KCStudly on Mon Apr 21, 2014 8:15 pm, edited 1 time in total.
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Re: About the types of foam...

Postby eaglesdare » Sun Mar 11, 2012 6:58 am

my hubby bought me a sheet of foam that had aluminum looking covering on one side. i never even used that piece. i went to the store and bought the stuff i wanted. i can't help with what is better than the other issue. i know what i used and it worked for me.

we do have a thread ( i believe it is a sticky) about foam. not sure if you have read that. i am not ignoring you, but as others know, i am not a technical person, so i can't answer questions when it comes to that.

i know discussions have taken place with using the beaded white foam, the pink foam, and the blue foam. i think mike is using the pink, i used the blue, as well as gpw.

i know most of us are using the 2" sheets, but another builder used smaller. i will get his link for you. (might be a few though, as i have to go out today).
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Re: About the types of foam...

Postby GPW » Sun Mar 11, 2012 7:43 am

Foams .... :o Many types of foam available ...
1. EPS expanded polystyrene ... what we know as the Blue/pink/green stuff ... and what beaded board is made of ... just a different process... Commonly available at the Box stores (HD , Lo’s) in the 2lb.’cu.ft. density ...
2. EPP expanded polypropylene ... Tough ,rubbery stuff , resistant to many solvents/glues/adhesives... comes in many densities ,from very light to very dense (car bumper grade ).. TOUGH , Pricy , Difficult to get ... Can be “structural“ ...Flexes instead of breaking ... Great “memory” ... Might even survive a frozen turkey ... :R
3. EPU expanded polyurethane ... Brown , open cell , many densities , Resists solvents ...gives off Toxic fumes when burned... Not something I’d think we’d want to use in a trailer ...
4. and more we’ve not yet explored , or have not been able to afford to explore .. :roll:

Just basic physics as with any thing else ... the thicker it is , the Stronger it is .... (what KC said ! ) I’ve been droning on about that for some time now .. The Bigger the trailer , the Thicker the foam .... The more dense the foam , the less you have to use ... The side benefit of thicker foam is the tremendous Insulation factor ... doesn’t take much to heat or cool it ... ;)

Now admittedly Foamies are Not for everybody .... :roll: Not as pretty as Wood , not as smooth as fiberglass... not as COOL as Aluminum ... :oops: But , it fills the need for those of us who are “past” tent camping ... yet Not ready to invest in a mobile wannabe’ version of our homes ... :roll:
THRIFTY in nature ... a good serviceable Foamie shouldn’t cost more than a really GOOD tent eh ?
EASY to fabricate , no special tools /skills required...

"Brag factor" :NC .... well you can’t have everything !!!! :roll: :lol:


When in doubt , refer to what KC said ... : “ The real strength is in what thickness foam and what skin material you use. Assuming you achieve a solid bond between skin and foam, the thicker you make the foam the stronger/stiffer your panel will be. The more robust you make your skin the more puncture resistant (i.e. 1/8 or 1/4 inch ply exterior might resist branches or frozen turkeys better than bed sheet or canvas and glue, or even fiberglass/epoxy). For this reason, I think the lower density/lighter versions of foam are preferred. The foam is not the strength. How far apart the skins are has much more effect on strength (the moment of inertia, I^4, goes up when the outer fibers of the stressed member are further apart). :thumbsup: :applause: 8)
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Re: About the types of foam...

Postby linuxmanxxx » Tue Mar 13, 2012 12:39 am

Yes you can pull the plastic coating off quite easily as I do that before I use it in all my sandwich wall builds.
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Re: About the types of foam...

Postby mdk » Tue Mar 13, 2012 2:26 am

linuxmanxxx wrote:Yes you can pull the plastic coating off quite easily as I do that before I use it in all my sandwich wall builds.


Ohh, great. Thanks!

Someone needs to compile all these questions... into a concise sticky...
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Re: question about foam

Postby SteveW » Tue Mar 13, 2012 8:20 pm

"Concise" and "Foam Discussion" don't really seem to go together around here. :lol:
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Re: question about foam

Postby KCStudly » Tue Mar 13, 2012 9:18 pm

Hey, no fair. We have stickies. ;) :roll: :D

Reading the long Thrifty thread is still a rite of Foamie passage, tho. 8)

Once you've done that you get 'Jumped In' and we give you a patch! (kidding)
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Re: question about foam

Postby eaglesdare » Wed Mar 14, 2012 7:43 am

yes we have stickies! :wine:

i try to take suggestions from foamlings and merge/move when suggested. hope this helps everyone.
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Re: question about foam

Postby Godfirst » Fri Jun 22, 2012 8:55 pm

New to forum,
Bought a foam teardrop couldn't pass it up paid only about 1000 bucks really cool and has some cool graphics on it the problem is the sides have a thin fiberglass veneer over the foam and is coming off the foam what should I do thinking of just using some wood screws to secure the panels.

Thanks
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Re: question about foam

Postby atahoekid » Fri Jun 22, 2012 9:54 pm

Godfirst wrote:New to forum,
Bought a foam teardrop couldn't pass it up paid only about 1000 bucks really cool and has some cool graphics on it the problem is the sides have a thin fiberglass veneer over the foam and is coming off the foam what should I do thinking of just using some wood screws to secure the panels.

Thanks
Duane


Welcome to the forum and the world of Foamies!!! :beer: :beer:

I assume by fiberglass veneer, you're talking about a fiberglass panel of some sort as opposed to a fiberglass cloth/epoxy skin. The problem with wood screws is trying to hit something solid under the veneer. The foam teardrops we're used to seeing/building don't have much of a frame and screws won't hold in the foam. You might be able to create a pocket of epoxy in the foam and then insert the fastener. If you go to West System Epoxy on-line, they talk about bonding fasteners and hardware. I have it in a User Manual but I'm pretty sure that info is on-line too. Or you might want to try to inject some glue or epoxy between the veneer and the foam core and then clamp it until it bonds. Or you might want to try both. Those are my thoughts... I'm sure there are others with other thoughts... Good Luck, Let us know how it goes
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Re: question about foam

Postby GPW » Sat Jun 23, 2012 5:12 am

Maybe just drill some small holes , inject some epoxy under the skin with one of those big plastic "Hypodemic nurdles “ :lol: ... worked for repairing damaged planes ... :thinking: The small holes would hardly be noticeable ...
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Re: question about foam

Postby Mary C » Mon Feb 11, 2013 4:41 pm

I would inject gripper, where's my patch ? I read the whole darn( Long) and exhausting funny and crazy thing and as a newbie I enjoyed it? speaking of that when is my right of passage? oh my quewstion about foam can you mix the blue and pink I have a sneaky feeling I might have to do that?

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Re: question about foam

Postby eaglesdare » Mon Feb 11, 2013 4:45 pm

while i am not the technical person here, i can only give you what i would think. so having said that: i don't see why you could not.
how was that? :lol:
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Re: question about foam

Postby Mary C » Mon Feb 11, 2013 5:11 pm

:lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: Thanks

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