Foam thickness and strength??

[tinksdad]

Wasn't sure which thread to put this in, so decided to start a new one. I have been busy in sketchup and designed several possible variations of what I hope my next trailer will be.

The problem: The search isn't over yet; but the only 4x8 sheets of foam I have been able to find locally are Foamular 150 --- 1 1/2" thickness. I really would like to use 250 or 350 if possible; but that may not be an option.

The Questions: Will the loss of 1/2" thickness create a problem? Will the 150 be structurally sound enough? I'm not sure I understand the numbering system; but I would believe 250 and 350 would be stronger than 150.

I'm hoping the "Experts" will have some thoughts on this. One idea that is running through my head at this time is the possibility of using smaller foam sections with some thin wooden ribs between the sections and around the perimeter to add some extra strength. It will still all be covered with canvas/TB, so wood rot should not be a problem (I hope). If it makes a difference, all my designs are planned around 5 foot wide and 5 foot tall (a crouchie) on a 4 x 8 base trailer. Basically modified Weekenders or Grasshoppers.


Edit: OOOPS!!!! After I posted this, I see in another thread about using a 1/2" plywood grid to add strength/stability.

[starleen2]

For those of us in the Southern Climates, 2" foam is hard to find. I was wondering about bonding two one inch pieces together - if that is possible

[GPW]

Should be easy to glue two sheets together... Gorilla glue spread thin , or maybe a WB contact cement ... Nice thing is you can bend the 1" foam , then glue the other on top ...

[eaglesdare]

i would like to throw in here that none of us are "experts". we seriously can only speak on what we have found during our builds and what experiences have been had with using certain glues.

i love that we are all out there throwing ideas around and asking questions. who knows what will come up next with the answers.

but i wanted to let everyone know i certaintly do not consider myself an expert by any means.


now as far as using 2 sheets together. i would make a guess and say yes, it could be done. i would think you would need to be careful of the gg as it expands, and it would seperate the two sheets. i would also think you could just wrap the two sheets together, pre canvas as a whole unit? perhaps?

[tinksdad]

i would like to throw in here that none of us are "experts". we seriously can only speak on what we have found during our builds and what experiences have been had with using certain glues.

That's why I put Experts in "quotes". I realize we are breaking new ground here and a lot of experimentation is happening. A lot of information has been posted and I'm still trying to wrap my head around some of the ideas and opinions. My main impetus was to try to get a discussion going on the pros and cons of the different strengths (150,250,350, etc..) of foam in different thicknesses. Like I stated in the OP, so far all I have been able to find locally is 1 1/2" 150. I don't want to waste my time and money if it might not be suitable.

[Conedodger]

I dont think anyone is going to say as we just dont now. Everyone is using what they can get local and they all differ. People are happy to find some at all and use what they can get

http://building.dow.com/na/en/products/insulation/rigidfoam.htm

This url lists the current Dow foams but they only list compression figures as this stuff in thier eyes is not for structural use unless its under compression. As GPW made clear on the first few pages of the "The big post" its the covering on each side that is the strength and the foam is simply keeping it apart.



This picture shows what its for, or for underfloor, i dont think you will ever see it used on its own, it always has at least on covering and normally two.

http://insulation.owenscorning.com/homeowners/insulation-products/foamular-150.aspx is for the Owens Corning Version with the Formular name

http://insulation.owenscorning.com/WorkArea/linkit.aspx?LinkIdentifier=id&ItemID=780 is the product data sheet

About 3/4 of the way down the second page it says

FoamulaR insulation is a non-structural material and must be installed on framings which are independently structurally adequate to meet required construction and service loading conditions

I think your question is the same as we all have, the data sheet says we have to fit it, in, on or skinned with something thats "independently structurally adequate", and its for each builder to make their own mind up if they are doing so.

I once wanted some metal tubing and asked for samples. The guy came to my office with them and went through how they could stand huge pressure, were suitable for high temperatures and could even be used with nasty chemicals, it was a fantastic presentation, but i was not to happy when i said I only wanted to make a chair leg so its horses for courses.

GPW and Eagle were breaking new ground and i have heard that their next project is making a Mars lander from tin foil, 2 baked bean cans, all stuck together with a bonding agent made from dried bread

Cant wait....

[Anita Rae]

We live in one of the areas where this stuff isn't available at the big stores. We contacted on of the small local building supply stores and they could order it for us. That might be an option for you.

GPW and Eagle were breaking new ground and i have heard that their next project is making a Mars lander from tin foil, 2 baked bean cans, all stuck together with a bonding agent made from dried bread

Cant wait....

Flour and water has been a reliable source of glue for generations.

[GPW]

I'm starting to think when they say structural, they're talking about uses in buildings , homes , etc. Where great weights and loads are expected ... for our small applications , it can indeed be "structural"... All how you read between the lines ... and how you use it !!!

[eaglesdare]

my husband says i should build one from all his beer cans. think that could be done? they build houses with them don't they? held together with mud right?
guess he will have to start drinking lots of beer.

[GPW]

How about using cut up beer can aluminum as an outer covering , applied like dragon scales ??? OK, I know that was silly .... it's still early .... more coffee...

[GPW]

Dad, bottom line , when in doubt make it Thicker ... Twice as thick is 8 times Stronger... The foam is the cheapest and lightest component , so feel free to make it much thicker... For gluing sheets of foam together ...one method we've used for airplanes was to thoroughly squeegee a very THIN coat of Gorilla glue on ,join the sheets , and then weight the surface .... no expansion noticeable ...Epoxy would work too.. Foam , being a homogeneous material joins easily , and I've made structures of made of many layers glued together , then shaped much as a block would ...No consideration of "grain" allows you to just add and subtract the material at will ...

[eaglesdare]

you know that could open up even more possibilites. glueing several layers together, you could make bed box frames, shelves, counters, just about everything could be done in foam huh? even though i am already a believer i think i am now even more of one.

i wonder about the white bead foam stuff. like the packing white foam. covered in canvas, several layers of that, could also make some inside elements. that stuff is cheaper in price. and its lighter also isn't it?

oh the possibilites. now back to dreaming about that lottery win.

[GPW]

Eagle , having used "bead board" for a lot of wings in the past ... it 's not as easily worked as the closed cell foam we use... the beads tending to tear away when cutting , makes sanding "difficult" also ... same problem ... But with a hot wire , you can easily cut out any shape you want ... and it seems to have better adhesion with T2, the glue soaking in between the beads... (all well tested)... comes in MANY weights .. same old story , to compensate for the less strength , just make it thicker ... I believe the foam we use (blue , Green, Pink) is about 2 lbs. / cu.ft. The bead board is usually half that ... but we've seen VERY dense bead board used for packing heavy items for shipping ... Haven't seen any of that commercially available ... yet ...
There is a large Insulation supplier in my area , I need to pay them a visit... wholesale only , but they offer many different types of foam( Styrofoam , EPS -expanded polystyrene-"bead board", and urethane foam , which must NOT be hot wired or burned ) and many different shapes , including large blocks ... and a good BS story always works , gotten much foam from them in the past for airplane construction ... just with an explanation ...

[GregDJ]

Tinksdad

You might try ordering extruded polystyrene from Universal Hovercraft. I have not ordered from them however by email they told me their foam's density is 2lb/cubic foot.

[Conedodger]

Found out a few things:

In the Owens corning Foamular foam the number refers to its maximum compressive strength

150 = 15psi
250 = 25psi
350 = 35psi

This test is to 10% compression or failure, and has to meet the figures

Also I have found some strength tests but they just seem way out to me.

The data sheet says they use test method ASTM C203

From Google:
Title: ASTM C203 is a standard Test Method for Breaking Load and Flexural Properties of Block-Type Thermal Insulation
Description : These test methods cover the determination of the breaking load and calculated flexural strength of a rectangular cross section of a preformed block-type thermal insulation tested as a simple beam.

150 - Flexural Strength (lb/cubic inch min) = 60
250 - Flexural Strength (lb/cubic inch min) = 75

Below is the machine to do the tests but it does not say how long the foam beam being tested is, the data sheet says "Value at yield or 5%, whichever occurs first."



Now I have no idea about this test but i cant see how a 1"x1" beam could stand 60 pounds one inch along it

Anyone have any idea?