Ruff, Alloy hit the nail on the head regarding overall strength. When building my own panels, I thought XPS was the best option due to the reasons you stated. Stiffness may not be ideal in a habitat on wheels. EPS actually has more bonding surface than XPS. CPT uses a two-part polyurethane glue to bond/vacuum their panels. I had previously thought epoxy was best due to strength. Having done my own testing over the years, the polyurethane bonds very well and allows for some flex without cracking. If you look at comparisons between different cores, PVC and EPS are close in characteristics except in weight and cost. Weight and R-value has been my top priority for this build. See link; https://www.cptpanels.com/composite-panels/materials/
DIY Composite Flatbed Camper Build
- Thread starter Terra Ops
- Start date
NOPEC
Well-known member
Yes I will but I am deathly slow.... I may not get the build done before they come for me.No worries, I get it nowAre you posting progress of your build?
rruff
Explorer
PVC @ 4lb is ~10x stronger, and even insulates better. Note that the R3 given for PVC foam is per 1/2" for some reason.
I made most of my walls ~1.5 lb/sq ft. The 1.5" PVC foam is ~.5 lb, and each skin is ~.5 lb. Yes, you can save some weight by making the foam lighter, but it won't be close to an equivalent structure, and it isn't something you can "fix" by making skins thicker or stronger.
I get impact from branches, rocks, birds, hail, people punching it with their fist, etc. Plus any place something is attached you need to be careful about spreading the load. I wouldn't have used light styrofoam without some framing in the core to keep everything together and provide hard points. Doesn't mean the light foam won't "work" without it, but it is relatively fragile.
rruff
Explorer
That thought crosses my mind every day...
I was referring to the CPT chart. https://www.cptpanels.com/composite-panels/materials/
Regarding lightest weight eps gets 5 pvc 3, both have equal insulation value, yes pvc is stronger and more durable. Pvc costs more. I'm satisfied with the EPS.
I got that one!
Alloy
Well-known member
Unicat has done something (custom) different for every month for XX years. Here at 2:30 & 14:00
Sika has a poor bond to bare aluminum that's why powder coating is used. Powder coating introduces a point of failure.
Going direct to aluminum, industry will use 3M 5200 or other (Henkel) adhesives.
I used the R value for Type II 16psi EPS . CPT uses the R value for Type II 20psi EPS.
Both slip and clamped are good systems. What system does CPT use to build van bodies?
Insulation inside aluminum and filling the corner are band aids. It's something to be aware of when choosing a box.
Perhaps we can get off the panel topic. I was hoping for some component input on this next build.
Would like for it to be all electric. 920 ah lithium will be the power and redarc the management. Anybody have thoughts on dry heat such as diesel or propex heater would put out only electric? Also looking at hot water options.
Would like for it to be all electric. 920 ah lithium will be the power and redarc the management. Anybody have thoughts on dry heat such as diesel or propex heater would put out only electric? Also looking at hot water options.
Alloy
Well-known member
I have Propex. It's low power consumption but it is single point (1 short duct) for heating air only.
Diesel hydronic heats air, truck (and vise versa) engine, hot (plate heat exchange) water and the tanks/valves (freeze protection) in the under body. Supplemental electric AC element will keep the hydronic system going when plugged into shore power or on a generator if the (Espar/Webasto/Aqua-hot) boiler breaks down.
rruff
Explorer
Inner and outer angles are a very simple and effective way to get a strong corner with zero thermal bridging.
He didn't give details on the foam or skins, but he did say the weight was ~11 kg/m^2 for the whole panel, which is ~2.2 lb/ft^2. That's pretty heavy... indicating that dense foam and thick skins are used.
I thought his "whack it with a hammer" test was interesting. I did quite a bit of that with a small sledgehammer. I found that carbon would crack more readily that fiberglass; same thickness for each, hand laid with epoxy. I suspect his carbon is a completely different system than the fiberglass skins he is using... probably infusion directly on the foam with very high fiber content and epoxy rather than polyester resin. The main advantage to carbon that I found was that it's ~3x the stiffness of fiberglass; it's only a little stronger and a little lighter. The higher stiffness with only a little more strength makes it more susceptible to impact.
Fair enough. If I may tho, I would like to comment on the following.
It seems from your posts that CPT responded quickly to some of the questions that came up earlier. Nice to see that kind of response from a mfr/supplier - vs ignoring - so that is worth noting imo.
Also glad the "rounded" look of the outer extrusion was mentioned. Might appeal to some buyers. It may even have a small aerodynamic benefit (Ford mentions a leading edge 60mm radius in their BB doc for E series boxes - for large panel boxes. And I see large radius on many 5 tons etc.) But I couldn't quantify the difference.
Anyway, I think we can agree choice is good. As interesting and informative as the construction discussion is - and it is to me - , these shell/campers won't be right for everyone. They may not satisfy one's "ultimate" or "best" search, nor necessarily the Marine, Military, Aerospace Spec so often sought after but they will have some appeal to some shoppers today (made in NA for eg). And the design may evolve in future.
Looking forward to following your build !
Thank you for that! It was getting a bit tiresome of the back and forth of opinions of those I know nothing about. While I too enjoy some discussion, it gets to a certain point where you start to wonder if they are doing more harm than good. Meaning opinions are taken out of context for the sake of just having something to say. I almost deleted this entire post as it felt hijacked. But I guess that's the nature of the beast. It did give me more to think about and I am more sure than before that this is the right path for me. The low weight and true four season capable is the main attraction of this product.
rruff
Explorer
Specifications for the foam used, the skins, the adhesive, and the method of assembly are important... I think...
A Plascore-based sandwich panel constructed with two layers of 3k carbon (skins) and a 4” thick (5 PPCF) core material is 50 Times stiffer than four layers of 3k carbon, alone. A sandwich panel with this same core and skin combination, but using an 8” core instead of a 4" thick core, is 180 Times stiffer than the skins alone. Weight increases by 33% going from solid skins to a 4” core and 60% (total) over the skins alone. This is a small price (in weight) to pay for the massive rigidity, impact absorption and load-spreading capabilities of a sandwich panel.
In any sandwich panel design, the skins carry tensile (30-42 ksi for 5086) and compressive loads (10M PSI for 5086), while the core carries the shear load (1600 – 2200 PSI for quality Structural foams, honeycombs, etc). So, you want a thick core (taller I-Beam) with high shear strength and skins that have high tensile and compressive strength. This is why EPS and XPS make terrible choices for a core material, regardless of your skin choice.
If these foams are chosen for their insulation properties, one must either build a robust "exo-cage" to carry the loads or have massively thick skins to do so. In either case, you have lost many/most of the benefits of the sandwich panel design. Further, I would contend that you don't have a sandwich panel at all. You simply have an insulated wall, just as you do in a house.
Can you build a 6' x 8' tear drop trailer using EPS, old bed sheets, and Elmer's glue? Sure. Go right ahead. That is one way to build a SIP/sandwich panel, but certainly not the right way or the best way, to do so.
Choose the best materials you can afford and do it right, once. If you cannot afford good quality products, you likely should not be building, as doing it 'upside-down-and-backwards' just finances the negative cash-flow over a long period of time.
In any sandwich panel design, the skins carry tensile (30-42 ksi for 5086) and compressive loads (10M PSI for 5086), while the core carries the shear load (1600 – 2200 PSI for quality Structural foams, honeycombs, etc). So, you want a thick core (taller I-Beam) with high shear strength and skins that have high tensile and compressive strength. This is why EPS and XPS make terrible choices for a core material, regardless of your skin choice.
If these foams are chosen for their insulation properties, one must either build a robust "exo-cage" to carry the loads or have massively thick skins to do so. In either case, you have lost many/most of the benefits of the sandwich panel design. Further, I would contend that you don't have a sandwich panel at all. You simply have an insulated wall, just as you do in a house.
Can you build a 6' x 8' tear drop trailer using EPS, old bed sheets, and Elmer's glue? Sure. Go right ahead. That is one way to build a SIP/sandwich panel, but certainly not the right way or the best way, to do so.
Choose the best materials you can afford and do it right, once. If you cannot afford good quality products, you likely should not be building, as doing it 'upside-down-and-backwards' just finances the negative cash-flow over a long period of time.
I've done diesel heaters on a couple of builds and like anything, they have their plusses and minus's. That said I'm going to use them on my current build.
The 2 tradeoffs I live with are the solenoid fuel pumps click pretty loud at night and the heaters like to be cycled hard to burn clean. Ideally the heater is sized to burn on high for at least 15 minutes before cycling off. They don't operate similar to a home furnace or propane furnace where you set and forget the thermostat. In my opinion, they are more like an on-off blow torch.
The good parts are that they are easy to install and easy to re-up fuel.
Looking back at your first CPT post it looks like your doing a flatbed. Have you sourced what flatbed you are using? Also what model truck is this going on?