Sintra (Expanded PVC) Sheet for Skin

[whiteryanc]

Hey All,

Been lurking for a few weeks now while considering making my own square-drop concept over the next year. The amount of information in here is mind boggling and I've begun to lean towards a Foamie-hybrid based primarily on my TV (Crosstrek) limitations. Hybrid because while I understand the PMF works great for people but I'm willing to save for a bit and spend a little more if this concept proves out, I also have a passion for overcomplicating my life. Truly, I have been really drawn to a CNC cut/routed panel system for cleanliness and easier construction on my end.

I know people have used a laminated XPS foam/Alu composite for construction but I was trying to come up with lighter (if possible) and cheaper options than using an aluminum composite. I've been diving deep into sign materials and came across Sintra (expanded PVC) sheets which are designed for long-term outdoor use and I can't find any posts regarding this type of material on the forum. Anyone test/have long term experience with this as an external skin?

I think I'm going to order some small pieces and mock up some laminations to sit out in the sun/weather for a few months since I won't be starting a build any time soon. It appears that a 2mm sheet (4ft x 8ft) is apx. 9.2 lbs so it the weight seems relatively reasonable when compared to PMF or similar skin options.

I am also considering a printed vinyl wrap as a final exterior layer for both color/graphics (I'm a designer...can't help myself) and additional UV resistance. Would love to hear some thoughts!

Here's the product information: https://www.coastalcreative.com/product/sintra-board-pvc-signs/

And an example of cost: http://www.artsupply.com/foamcore/sintraboard.htm

Thanks and looking forward to diving deeper into the forum!
Ryan

[pchast]

The only concern I can see to investigate is if there is any difference in coefficient of
expansion with the materials used.

[Pmullen503]

+1 on thermal expansion. But if the core is foam, it does have some give so it would work. Commercial SIPS are wood and foam which have quite different TEC. The key would be a good lamination; the right adhesive and good clamping.

[whiteryanc]

+1 on thermal expansion. But if the core is foam, it does have some give so it would work. Commercial SIPS are wood and foam which have quite different TEC. The key would be a good lamination; the right adhesive and good clamping.

That is definitely a consideration, I've been researching the properties and they seem to have minimal thermal expansion that could be mitigated by proper prep/lamination as you point out with SIPS panels. https://www.curbellplastics.com/Researc ... tion-Guide

The other thing is while I'm not designing this to be disposed of, I see this as "Version 1" of what I imagine will be a multi-year journey of designing and building so I'm willing to test out some theories that may only last a few years with the expectation that I'll always be planning my next build (as long as they are reliable for at least a season).

Thanks!

[OP827]

Test panels might not give a full picture of camper structure behavior in different temperatures. What structural materials will be used to attach panels together, windows, doors, what is interior skin material. All those should considered for thermal expansion issues. Steel, and especially wood and plywood have much lower TEC than non-reinforced plastics such as PVC. Temperature change stress will be taken by the glues and structure and may be causing some deformations or in extreme case - joint or failures. The thinner the skin, the less stress it will be able to put on the structure by stressing (stretching or compressing) itself. Building a fair test panel, it is better to include all different structural materials and then scale the thicknesses and dimensions accordingly. I will follow with interest as I am also looking for optimal sandwich panel design. Thanks for sharing your thoughts here

[whiteryanc]

Test panels might not give a full picture of camper structure behavior in different temperatures. What structural materials will be used to attach panels together, windows, doors, what is interior skin material. All those should considered for thermal expansion issues. Steel, and especially wood and plywood have much lower TEC than non-reinforced plastics such as PVC. Temperature change stress will be taken by the glues and structure and may be causing some deformations or in extreme case - joint or failures. The thinner the skin, the less stress it will be able to put on the structure by stressing (stretching or compressing) itself. Building a fair test panel, it is better to include all different structural materials and then scale the thicknesses and dimensions accordingly. I will follow with interest as I am also looking for optimal sandwich panel design. Thanks for sharing your thoughts here

Good point with the structural elements. My current thought is incredibly minimal aluminum frame (just a few wall supports/roof trusses to help securely attach roof and walls to the base in addition to adhesive) similar to that of the Northern Lights trailer http://www.tnttt.com/viewtopic.php?f=27&t=51991 but with even less structure. I'd honestly like the structure to be secondary to the strength of the panels, more just a tool for aligning and tying things together. The idea would be to use the laminated panels as the primary structure similar to the StyroMax items I've seen mentioned and watched on YT https://www.youtube.com/watch?v=vlEfjmqbT3g to minimize weight/cost/thermal bridging. Of course I really have no idea what I'm doing but based on my research so far it appears a well-laminated panel should be sufficient for the size square drop I want to make (around 5x8).

[saltydawg]

I am a firm believer in SIPs. But I would avoid PVC, it is hard to glue with the exception of solvents. Epoxy will not bond to it.

If you want to do a light weight panel there is a couple of companies who make some interesting stuff.

I want to reach out to carbon core about their panels. They make honeycomb, and sips.

[OP827]

The smaller trailer panels are the less stress is built due to thermal expansion. I agree with your minimal framing approach. Structural sandwich panels only need hard points for various attachments. Framing is not really required. What glues are suitable and weather heat resistant for this PVC foam skin? Many glues will soften under hot sun to the point that parts can separate. My build failed wood frame windows with acrylic only glued to them is a good example of that. Dark surface will heat up under sun really good and fast.

I personally feel that fiber reinforced plastic maybe a better option for exterior skin