Teardrops n Tiny Travel Trailers

Hi everyone,

Happy New Year etc!

Its been awhile since I was last on here, I have been distracted by many things recently.

I have been planning a foamie for awhile now, (well have been going back to steam bent oak frame construction occasionally but am put off by amount of work needed) anyway I really want Aluminum sides/top and I would like a birch ply interior. Much like the Atma Tear!

Anyway I have stumbled on a form of construction which is apparently common in the US but less so in the UK, SIP (structrual insulated panels) these comprise of a foam core ususally expanded polystrene with a layer of wood either side. usually OSB I think. Anyway this is apparently really strong and light etc. I have also found out that SIPS can also have metal skins which made me think, I could just make a SIP panel that comprised of a 3mm (sorry for the metric ) birch ply on one side, and a 1mm panel of aluminum on the other, with an expanded polystrene 50mm core.

I have made a test panel out of 50mm foam, 0.5mm alu (B&Q wanted an insane amount for 1mm alu plate) and a 6mm hardwood ply, (again birch ply is expensive in small amounts! Anyway I glued the alu to the foam using Gorilla Glue and the ply to the foam using titebond and the resulting panel is really light and strong. I can stand on the panel with it across two chairs with only 10mm on either side on the chair and there is no deflection or deformation, I am working my way up to jumping up and down! I was thinking I could almost get away with 0.5mm aluminum but it does dent far too easily.

Anyway it took me awhile to get a nice layer of GG and Titebond on either side of the foam (and it was quite a small test piece) and I was wondering how much time do you have before GG or titebond will cure? I realise this is probably dependant on ambient conditions! but some experiences would be nice!

This form of construction really appeals (as it uses the mimimum amount of materials), but I still trying to work out the details, the main one being how to join the panels together, I am thinking of using the same sort of construction as ghcoe is using, eg making the foam panels lock together, then taking the foam pieces and gluing the wood and aluminum on, then I would assemble them together. I know that canvas and paint create a "sock" effect and I was wondering if the aluminum trim would create a similar effect? and on the inside using something to join the wood panels together would that also help?

Hopefully that makes some sort of sense,

Many Thanks

Tom

That sounds workable Tom , but there are many unanswered questions about foam and aluminum ... long term adhesion , expansion and contraction with the foam , and the possibility of lifting , wrinkling later , and the question of how to join the panels with the Al....

hmmmm good point about the expansion of al in the sun, shame its not sunny as I could put the test piece in the sun! (I could probably fit it in the oven! but I doubt I would get away with that!

I wonder how the al skins are bonded in SIP panels..............

EDIT: have down some quick research as it seems that the al will expand about 0.1 inches over the 120 inch length of my planned teardrop over a 70 degree F temperature change. That doesn't seem so bad?

EDIT2: If anything the polystrene will expand more, I calculate it will expand 0.3 inches in the same scenario.

Can GG cope with that kind of stress?

That’s the question eh ? The best adhesive.... One thing we’ve noticed on Cargo trailers around here... The ones that were constructed in the warm summer months when the metal was fully expanded , only contracted in the winter, and never seemed to show any wrinkling in any season ... That may be an advantage applied over foam ...

One thing that comes to mind is sanding the surface of the Al to be glued, just for better adhesion ... more “tooth” to the surface , expanding the gluing area.

For joining panels , it would seem a soft aluminum right angle moulding that was sealed/ riveted in the conventional manner would be the most common way ...

I've built 3 with 3m 30nf contact adhesive on both sides aluminum on exterior but I used 5mm underlayment on exterior and .32 aluminum over because without it shows a very uneven surface. Plus the wood and thinner aluminum block the denting and is cheaper and easier to work with.

Plus this way skinning aluminum after build fixes your problems of attachment because however you attach (mine was screws outside to inside) the aluminum will cover and seal after.

Aluminum as a sips panel has been used for years in refrigerated truck bodies and McVeighs in the north west (UK) made sips panels. I can't find them but can find http://www.mcveighoffsite.com/ who may be able to help.
From memory they used PU (expanding foam in a jig) to make the panels not EPS. Titebond III is the glue to use or a D9 PVA (external PVA) glue to stick timber to EPS. Just watch the temperature; it's too cold in the UK now for the glue to cure. I used a 150w lamp to keep it warm in the garage. Watch fire risk....

The downside with using a sip panel is that is does not bend (for a TD roof for example) It may be worth considering using foam/fibreglass or some of the options in the foamie section. I've been researching using strip planking but rather than use wood, use foam. This allows all kinds of interesting shapes and it's cheap. Take a look at uksips.org if you need any info, particularly about buying EPS in reasonable sizes, the block from the factory is 1200x1200x4800 and the cut it down into smaller sizes.

Good luck!

Hi Grant,

Thanks for the info, you put me onto sips in the first place. Am glad about the adhesive advice as titebond 3 is expensive here!

Is is not possible to build a bent panel? Could I not kerf the foam to bend it then glue the wood and ali to each side?

I won'tbe building to later in the yyear as I will have to build it outside! (Am on the look out for a garage).

Thanks for the links, will have a look!

Linuxman: yes I have been advised about contact adhesive on here before, but have not found a decent source, its quite expensive over here!

Thanks for all the advice so far!

Grrrr…....

The aluminium came off the foam when I pulled at a corner. The foam didn't really adhere to the metal! The wood really did at least!

So a contact adhesive would work better? Think I found some, scotchgrip 10, I haven't found the adhesive mentioned by linuxman. But this says it bonds aluminium so hopefully will work!

Cheers

Trogdor wrote:I still trying to work out the details, the main one being how to join the panels together

That's always the case with cored constructions, plus you also need to look at how you will join internal parts (like bulkhead, shelves) to the exterior. You can add wood strips instead of core at these points, but then you're really building a wood-framed body, but with the foam glued in - the little bit of wood framing will provide 90% of strength needed.

There's no problem to making your own curved cored panel, you just have to build it curved. It's bending a flat cored panel into a curved shape that's difficult/impossible.

If you do foam wood then aluminum you can use any of the readily available contact cements since you don't have to worry about melting the foam and they are cheaper just ultra nasty to work with.

The technical details of how to join SIPs panels together is here http://www.sipsindustries.com.au/technical-documents
Download the technical details. The guys in Oz have done a great job!

Here're a couple of Foamie section threads on the topic
that may be of use to you:

Mini SIPs As A Foamy Technique
viewtopic.php?f=55&t=54740

Interesting reading about foam core panels.
viewtopic.php?f=55&t=48850

Cheers,
Norm/mezmo

Hi,

Grantstew8: Thanks for the links the one showing how SIPS are constructed it has been really useful, as I can now see how to fit the panels together!

Mezmo: thanks for those links, I didn't realise SIPS had been mentioned on here before! Some useful info there.

Linuxman: you mention using .32" aluminium, I am assuming you mean .032? this would be about 0.8mm rather than 8mm!

I think I will be using 1/8" external ply for my skins as I can get that for £8.25 for an 4 by 8 sheet. I can get the foam for about 15.00 for an 50mm thick 4 by 8 sheet as well so I can build the trailer for not too much money! the alu is going to cost me tho!

Thanks for the help so far everyone

Trog , are you dead set on Aluminum ??? We will try to convince you otherwise...