Epoxy/Styrofoam Test Panels

[Wobbly Wheels]

It started in this thread:
http://tnttt.com/viewtopic.php?t=44145
and now has a home of its own.

Pasted by way of intro:
"It's not pertinent to canvas really and may not even be relevant to 'thrifty' (at least not generally, though it is for me), but for my build I'll be glassing over the foam. I've been building boats a long time so I have the tooling and the experience, but if one didn't then I think the canvas is a great idea...and ingenious.

As far as using glass cloth with glue, my biggest concern would be ensuring that the cloth is fully saturated. If it's not, any dry fibers will wick moisture and hold it next to the foam. Temperature changes will cause bubbles to stand out and of course you'll get mold/mildew there too. To do that, I'd put the precut glass into a large freezer bag, dump the glue in, squeeze the air out, and go at it with a rolling pin to ensure it's fully wetted. I do that with epoxy layups and it economizes the epoxy (less drips onto the floor). A piece of 3" ABS sewer pipe makes a great roller.

To be completely fair, I haven't tested glue on glass cloth - those are generalizations about resin-starved layups, but dry cloth is dry cloth. The same capillary action that wets the cloth with resin also works on water (and should work on glue too). Personally, I wouldn't use glass mat at all but that's jmho.

I have made up some test pieces to see how structural joints with epoxy, 6oz cloth and 1" foam will perform. I've used EPS (styro)foam & epoxy together before but only for plugs and molds - never for structural panels.

Here is a link to a photobucket album with pics of the test pieces I made - one is an outside corner, one is a panel seam and one is a tab applied to unsanded foam to see the difference in bond strength between sanding and not sanding the foam before layup. When I've got my answers, I'll post up a thread to share what I found out. The next step is to build a scale shell once I figure out how to scale the cloth weight down.
6oz cloth would be overkill for a 1/10 scale model of the body.

EDIT - upping the pics and vid now...I'll make most of this post into its own thread later. I was most surprised that it didn't seem to make a difference whether the foam was sanded or not - that seems counter-intuitive to me. Of course, it applies to epoxy and not T2/T3..."

[Wobbly Wheels]

Quoted from GPW:
W2, I think for maximum foam adhesion a perforating tool would be the item to have http://www.amazon.com/Warner-250-Tool-c ... 711&sr=8-4
Especially with epoxy which would form thousands of little epoxy nails to better hold the skin on ... JMHO...

That's a great idea - I think this old dog just learned a new trick. In seeing the results, I think that would be a better option since, at first blush, sanding didn't seem to make much of a difference. In a pull test, though I'm guessing sanding would help a lot with shear ('sliding') loads as shown by trying to bend that corner piece in tension.

[Wobbly Wheels]

Quoted from Conedodger:
Great tests and your findings are pretty much the same as all the others I have seen. I take it your tests are only one layer. The vid where you are bending the tab joint shows the strength it has, if you had done it on both sides I dont think it would have broken at all. However one thing is clear, once it goes its had it and it has no strength whatsoever and from my tests the same goes for T2 and cloth. Also once it starts to peel its easy to get off.

If we can produce something that stops the initial movement I am sure it would never move.

My fear is the join between the floor and the foam, the last thing I want is to arrive in Mid-spain after a 15 hour drive to find all i had left was a 6' x 8' piece of flat board

Funny thing about tabbing both sides....I wasn't too worried about that part of it because I will have 1/8" ply laminated to the inside, but you've gotten me thinking about doing the seams first. I don't know if it shows up in the vid, but I sanded in a rabbet for the tab so it wouldn't stand proud of the surface. The cloth used to sheath the entire thing would be laid up over top so there would indeed be two units (layers) of cloth over the seam. I agree that taping the inside would increase the strength of the shell by a lot.

[GPW]

W2, I was thinking of something like this as an alternative ... lots of mechanical fasteners...

[mikeschn]

GPW,

Do you think this way now because you have built a foamie?

Mike...

[GPW]

Mike , actually not , just thinking ahead for the Next one ... These Foamies' are like Potato chips , you can't have just one...
My next one (bigger) will have the ply/ paneling wall inside ...

The one I have now without that seems to be STOUT as is ... but it is a smaller more traditional TD size.. Will add some inner reinforcing strips when we get around to the interior ... soon we hope ...
I already think there's a bit of overbuilding on these already (or planned overbuilding) The light shell shouldn't cause any undue stress on the floor to wall join ... Mass X inertia... Low mass , less to try and rip itself apart ... save Bear attacks ...

A far as the foam surviving high speed towing , I've designed and built many RC planes of 1/4" foam , hot glued , No reinforcing , and they fly over 100mph and don't come apart ..... unless they crash of course , and then the damage is Much less than say a Balsa plane ... usually a quick field repair with a hot glue gun ... The flexibility of the foam allows it to bend more without breaking ... But gotta' plan ahead ...you know how some people drive

[Wobbly Wheels]

That would indeed be a pretty skookum way to attach the walls, given all that glue area between the foam and ply to spread the loading.

For better or worse, I'd like to eliminate fasteners wherever possible and incorporate the floor into the monocoque rather than having the shell attached on its own to the floor. I'm going to be pulling it up logging roads with my 4cyl Ranger, so I don't want to be hauling anything extra in the trailer....especially if I'm packing camping/hunting gear for a week's boondocking as well. Overnight trips are fine

I think I'm going to build a SIP-style floor (foam with cladding) and build the shell off the trailer - and if it's light enough I can just keep rolling it over to get 'er done !
That will let me start making foamie 'snow' AND keep using the donor tent trailer through the summer. Woohoo, win-win for me !

I figure I'll either miter or lap the floor/wall joint to maximize the foam-on-foam gluing area, then do the layup as tabs in and out and sheathing over everything on the outside. Once the shell is complete, I think the interior tabbing would become redundant...but they don't weigh anything so it's ok.

Now if only I could draw with a keyboard and mouse, lol.

[GPW]

W2, for really rough situations , like logging roads, just Epoxy/fiberglass the whole thing and be done with the worry eh ... extra glass where you think you need it ... would be like a Tank !!! ... a highly insulated Tank !!!

Any fears about foam , just look at those ice chest/coolers/igloos we've used and abused for years ... just a little plastic skin inside and out ... still around... still working ... Still have my metal covered Coleman ... That's gotta' be Old ...

[mikeschn]

W² I'd love to see your SIP design!

Mike...

[GPW]

Just a reminder, the whole reason we used foam was to eliminate the possibility of ROT and de-lam ... the more wood you use , the more possibility of the afore mentioned maladies which seem to curse all wooden teardrops ...

[mikeschn]

Just a reminder, the whole reason we used foam was to eliminate the possibility of ROT and de-lam ... the more wood you use , the more possibility of the afore mentioned maladies which seem to curse all wooden teardrops ...

Well, of course!

But it seems we can not eliminate wood entirely.

So can we say that wood on the inside of the trailer is okay, while wood on the outside of the trailer is at risk? Of course that means window frames and door frames are at risk, unless they are covered with canvas and T2, right?

Mike...

[GPW]

Right!!!

[eaglesdare]

i think it could be almost without wood. perhaps the size would make a difference. since we started discussing foam covered with canvas as shelves and such..looking at how my trailer was build, i honestly believe that we could have only used the wood spars.
..i have that 1/2 wall bulkhead/bunkbed, made out of wood. i know for my size this could have been done with the 2" foam.
even the spars in mine could possibly be removed. we used them to hold down the curve on the foam on the roof. but i believe that once it was covered in canvas, the spars wouldn't have been necessary.

but i personally would use the spars. and in the second one i still plan to use them. now the bulkhead walls? i am going to attempt as wood free as possible, or at least as confortable as i can get.

my point being that i think size might have a lot to do with how much wood one needs or feels confident with.

[GPW]

Bigger trailers , Thicker Foam !!! Imagine how strong a 4" thick wall would be ... Twice as thick is EIGHT times as Strong !!!

[eaglesdare]

while i agree with what you say, i wouldn't double up the foam. in my case i am building wider for the space, it would defeat the purpose if i fill that space in with more foam.