foams and there structural strengths

[darkghost]

Starting this here rather then messing up this thread http://mikenchell.com/forums/viewtopic. ... sc&start=0 in any case I am wanting to start a small trailer and am wanting to use foam with fiberglass and epoxy covering. What I am looking for is strengths of all the foams so far I know pink foam and divinicells strengths I am now looking into polyiso and polyurathane. Also looking for ideas on how to laminate it to stop delamination from occurring. Thanx for any input Jim Morrison

[angib]

I've used polyiso (PIR) foam for insulation in my house and I'm sure it would be a good structural core - it certainly has a high compressive strength - but I've never seen any strength data for it. Over here, it has the additional problem that it's only readily available with foil facings which would completely prevent its use as a core.

If you are laminating wet epoxy/glass onto foam then you don't need any preparation. The descriptions of fiberglass 'delaminating' from pink foam are simply structural failure of the foam right next to the laminate, where the stress is highest, because pink foam is weak as s**t.

If you want to bond ready-made fiberglass sheets onto foam, that's a quite different process - the question here is how will you apply pressure all over the surface. Finding a suitable bonding adhesive (such as thickened epoxy) is easy, it's clamping the two surfaces together that's tricky.

Andrew

[bobhenry]

Here is how to save a lot of work if you can locate a distributor in your area.

http://www.citadelap.com/glazeguard1000wr.htm

sheets available up to 5 x 12

[angib]

That looks like very nice stuff - ready-finished, decently lightweight and, at under 1" thick, the right thickness for this application.

But......... as with all pre-made panels, there's the same two problems:

- How do you make a structural joint? The way it's shown as an alternative to a glazed panel, in a frame, suggests the manufacturers don't think there's a way to join it.

- Can it be bent around the curves of a teardrop? If it's a structural sandwich, then the answer is always 'no'.

Andrew

[darkghost]

I am thinking of using polyurethane sheets as I found them in 2"X4'X8' but they are not all that cheap at 140$ apiece but I figure that I only want to build this thing once so I guess I should spare no expense. The design is either going to be my version of a road toad or a winter warrior (havn't got that far yet) it will be foam with glass cloth epoxied to it. My reason is light weight as my tow vehicle is a samurai so my max is 1000Lbs also I live in B.C. and do alot of spring and fall camping as I pick mushrooms on a commercial level. So I need the insulation value as I boondock for 1-3 months at a time well off the beaten trail. Right now I am trying to figure out how to do this and keep it light and strong as possible so any help would be muchly appreciated. Thanx Jim Morrison

[wannabefree]

When I first started plotting my tear I gave some thought to building walls and roof sandwich style with 3mm ply skins, 12mm framing, and blown in foam. Should be very rigid and light. I nixed it because I felt like I was taking on enough risk for a first effort. Has anyone out there experimented with blown in foam?

[angib]

Has anyone out there experimented with blown in foam?

I've seen it used in boats, but only with really heavy support to stop the two skins bowing out - which is the problem I'd expect in trying to use it on a trailer.

I think you might have to conduct some tests to find out exactly how much liquid to pout into each space so that it foamed the whole space but didn't spread the outer skins.

Andrew

[wannabefree]

Andrew - yep, that's why I stuck with convention. I'd still like to try it someday, but not without a lot of experimenting.

[jdarkoregon]

DarkGhost,

I REALLY like your way of thinking, but I don't understand why you care about the strength of the foam. Aren't you covering it with fiberglass? Won't that be the strength and the foam will just be the shape.

John

What is the shape you are thinking about

[darkghost]

The thing is that this will be pulled through some nasty terrain so yes the fiberglass will be the main structural support but if a branch or rock happens to come in contact with the trailer I want reasurance that my fancy little bedroom will survive. So I orderd some polyurethane yesterday and grabbed a gallon of west system along with a few yards of 1.5oz and 6oz cloth along with some 2" EPS so all I have to do is wait for the urethane to show up. The next thing I need to figure out is how to surface prep the foam so I get good adhersion so that I dont need to worry about delamination issues which I am worried about. I was thinking about cutting the foam into 1 foot strips wraping them in glass then laminating them together to form the walls that way they have a rib of glass every foot or so I figure that may give me the strength I am looking for. In the mean time when it gets dryer out I will start my testing of the composite panels strength to see if I can figure out the shear strength of diffrent types of layups so stay tuned and I will see what happens. Cheers Jim Morrison

[moreforles]

keep us posted as it progresses as myself and probably many others are thinking about using the same technigue....

I got interested in it when thinking about building a homemade car, call the Tri-Magnum.... used a motor cycle for rear wheel power supply, with front end from vw? or similar ..... plywood bulkheads with foam sheets and fiberglass covering....

I didn't care much for the motor cycle as power supply and reengineered it to use a single rear wheel, but a front wheel drive vehicle as power supply.....

I good for planning, but most projects rarely get past that point... (genetic flaw.... inherited from my dad.....)

but camper still in planning stage, so it still has a chance....

foam and fiberglass exterior, interior? (still thinking about that..... ) I have a lot of wood trim and components from stripped RV's and conversion vans, and would like to modifiy them into it, make it looks like they belong there, not just thrown in and put to use...

[jdarkoregon]

Ghost, 1 foot strips wrapped, that sounds strong, and you could be hiding conduit in the foam if you wanted.

Hummmm, thats interesting. You need to check out the build by Gaston, he's a great guy and he might be available to bounce ideas off

John

[jimqpublic]

It may just be the money, but I would think there is a reason that XPS (Extruded Polystyrene) at R-5 per inch is the standard for panels instead of Polyisocyanurate at R-7 per inch. Polyiso is also stable at higher temperature than XPS (250F vs. 180F). A black skin over XPS might get too hot in the sun. Polyiso can also handle solvent exposure without melting.

I suspect that Polyiso is more likely to crumble from vibration than XPS, but that's just a guess. Otherwise why isn't anyone using it in RV's?

My ideal foam for building flat wall and floor panels for a winter trailer would be 1.5" Dow Panel Core 40 (2.0 pound per cubic foot extruded polystyrene, milled to exact thickness). For a curved roof you could use the same by kerfing it.
http://building.dow.com/na/en/products/insulation/panelcore40.htm Panelcore 40 at 2 pounds per cubic foot would only add 25 pounds over Panelcore 20 at 1.5 pounds per cubic foot for my "dream" canned ham, but it's twice as strong.

[RepairmanJack]

Hi Darkghost!
I'm new to the scene but when I first started thinking of a design etc. one of the first things that popped into my head was an article I saw years and years ago in Popular Mechanics ( I think! ) They built a car that looked similar to a Delorean out of glass wrapped foam with plywood bulkheads. If I remember correctly it was blue board but for the life of me I cannot remember exacty what type of resin was used. For what I am planning for my build, a modified "modernistic", that too is what I have in mind. Bit more freedom as far contours etc. go and less framing that I really like. Keep us posted as to your progress 'cause another one up here in the frozen north is going to be doing the same once the weather turns!!!!
Cheers
Jack

[Dark Horse]

Structural foams are used in boat building, unless you have access to a vacumm bag of sufficient size for the entire panel you will have alot of weight in exess resin - enough so that the larger custom boats still use plywood composite construction, not counting the cost difference. The boats still use internal framing for load support as the Foam is mostly used as a skin even in stitch and glue construction

Some boat material suppliers will sell preglassed panels, but bending them is difficult, they are attached to each other with Epoxy and fiberglass