DIY Composite Flatbed Camper Build

[rruff]

It doesn't look ideal... but it seems robust compared to how Styromax does their edges! Although theirs have some overlap so would be better thermally.

Speaking of insulation, the PP honeycomb isn't the best in that department... thinking of the options they list, PVC foam would be the way to go.

 

[IdaSHO]

Acid#8 needs a barrier coat before waterborne coatings are applied.
It also has a 60min open time before sanding is required which means a poor chemical bond after 60 min.

That may be true, but first you said adhesive, then coating.
Specifically, which adhesives and coatings are you referring to, that is relevant to this?

And with regards to chemical bonds, which aluminum primer would provide a great chemical bond after 1-hour?

 

[Terra Ops]

Acid#8 needs a barrier coat before waterborne coatings are applied. It also has a 60min open time before sanding is required which means a poor chemical bond after 60 min.

I'd follow the adhesive mfg.'s system.

Another reason for primer (which I may have missed being mentioned here) is to reduce (corrosion creep) electrolysis. Many (x 1000) times I've seen a paint and adhesives fail due to electrolysis between ( often mechanical) coating and aluminum.


No cleaning/sanding prep or primer is shown (OK for a small box?) here which I think is a mistake.


One of the issues is the bond isn't to aluminum but to powder (done offshore??) coating. If it was me I'd buy the bare (or have it stripped) extrusions and build the box using the adhesive mfg.'s system. Having it look pretty isn't worth loosing the ability to weld or having to repair (next to impossible) the powder coating.

I also don't like the lack of insulation (condensation) in the corners. For this Boxxed and TC is a better design.

Not sure if primer is being used as you mentioned, but I will be sure to inquire and follow up. They have been in the transportation industry for over 20 years, I would think they know what they are doing.
The two-piece aluminum extrusion gives 100% thermal transfer free from the exterior aluminum. With a slip-on one-piece extrusion, you’re doing exactly that, just slipping it on. It works well, but it also drags the glue out of the glue channels which can give an inconsistent bond. Using a two-piece assembly method, these are pressed on, optimizing the glue adhesion. The corner caps are aluminum as well and both are powder coated. CPT also provides a foam insert into the corner cavity, but I feel this is a moot point. Temperature cannot transfer if there is no medium to transfer through. I would also suggest the FRP extrusions are not only heavier than aluminum they do transfer "some" temps.

 

[NOPEC]

It doesn't look ideal... but it seems robust compared to how Styromax does their edges! Although theirs have some overlap so would be better thermally.

Speaking of insulation, the PP honeycomb isn't the best in that department... thinking of the options they list, PVC foam would be the way to go.

rruff - CPT uses the HCPP panels in their industrial slide in ambulances. These panels and the style of build, allow them to market a MTC (mobile treatment center) which is strong enough to endure a roll over, thus they are not required to have an auxiliary roll cage, which some of the competitors require. The national licensing agency folks are very strict about such things. That being said, CPT is the first to admit that HC panels basically have virtually no insulation value, that is why for their non industrial campers, they are using a foam core instead.

 

[rruff]

CPT is the first to admit that HC panels basically have virtually no insulation value, that is why for their non industrial campers, they are using a foam core instead.

Do you know the specs on your core and skins?

 

[Alloy]

That may be true, but first you said adhesive, then coating.
Specifically, which adhesives and coatings are you referring to, that is relevant to this?

And with regards to chemical bonds, which aluminum primer would provide a great chemical bond after 1-hour?

Acid#8 specs refer to coatings. I expanded on it saying I'd be reluctant to (be the test model) use it with moisture cure caulking.


Alodine

BONDERITE® M-CR 1200 AERO

BONDERITE M-CR 1200 AERO is a powdered chemical used to produce a protective coating on aluminum which ranges in color from light iridescent gold to tan. The process is operated at room temperature. The coating produced minimizes corrosion and provides an improved bond for paint.

www.henkel-adhesives.com

 

[NOPEC]

Do you know the specs on your core and skins?

Mine walls are a touch over 1.5", so guessing around R7.5

 

[IdaSHO]

Acid#8 specs refer to coatings. I expanded on it saying I'd be reluctant to (be the test model) use it with moisture cure caulking.

So entirely speculation? And now whats this about caulking?

Again, Ive never had a failure associated with Acid#8
While I have never used any moisture cure adhesives, coatings, or CAULKING with it, as thats just silly, it bonds to tough metals including aluminum. And no silly prep or application nonsense like Alodine. Seriously, no matter how good it may be…. read the data sheets on that stuff. Acid #8 can be brushed/rolled/sprayed right out of the can with nothing more than sand/degloss and solvent wipe.

 

[rruff]

Mine walls are a touch over 1.5", so guessing around R7.5

I was thinking more the type and density of foam... and the thickness and layup of the FRP.

 

[Alloy]

Not sure if primer is being used as you mentioned, but I will be sure to inquire and follow up. They have been in the transportation industry for over 20 years, I would think they know what they are doing.
The two-piece aluminum extrusion gives 100% thermal transfer free from the exterior aluminum. With a slip-on one-piece extrusion, you’re doing exactly that, just slipping it on. It works well, but it also drags the glue out of the glue channels which can give an inconsistent bond. Using a two-piece assembly method, these are pressed on, optimizing the glue adhesion. The corner caps are aluminum as well and both are powder coated. CPT also provides a foam insert into the corner cavity, but I feel this is a moot point. Temperature cannot transfer if there is no medium to transfer through. I would also suggest the FRP extrusions are not only heavier than aluminum they do transfer "some" temps.

I'm always suspect when told someone has done something for XX number of years or they've XX years experience. The question is always have they been doing the same thing (production line) every month for XX years or have they done something (custom) different for every month for XX years.

There are other factors beside the width of the bond.

FRP is an insulator. Aluminum is the opposite and transfers heat/cold 300X faster than FRP.

R value of 2" Type II (worse if it's Type I) EPS is +/-R8
There has to be a vacuum (very few atoms) to stop conductive (not radiant) heat transfer. There is conductive heat transfer through (the atoms in) air which has an R value of +/-0.9.

Between the outside and inside corner looks to be 1.5" air gap so the corners are +/-R1.8 and the screws don't help.

 

[Alloy]

Mine walls are a touch over 1.5", so guessing around R7.5

1.5" Type I EPS is R-5.62

1.5" Type II EPS is R-6.06

 

[NOPEC]

I'm always suspect when told someone has done something for XX number of years or they've XX years experience. The question is always have they been doing the same thing (production line) every month for XX years or have they done something (custom) different for every month for XX years.

There are other factors beside the width of the bond.

FRP is an insulator. Aluminum is the opposite and transfers heat/cold 300X faster than FRP.

R value of 2" Type II (worse if it's Type I) EPS is +/-R8
There has to be a vacuum (very few atoms) to stop conductive (not radiant) heat transfer. There is conductive heat transfer through (the atoms in) air which has an R value of +/-0.9.

Between the outside and inside corner looks to be 1.5" air gap so the corners are +/-R1.8 and the screws don't help.

View attachment 803245

Alloy
I have one of first CPT campers, pretty much a prototype and I acted in part as a guinea pig in exchange for having a fair bit of input into my own design. I am very much still enjoying it and the continuing steep curve that occurs with interior self builds.

That being said, I would agree with a lot of what you have mentioned regarding the R value of the corners. The CPT units come from an industrial background (as you well know) and I was well aware of the potential around thermal shortcomings with their MTC units. I had discussions around this issue with CPT at the design phase and I was mostly instrumental in getting wire cut rigid foam profiles matching the large cavity, which were inserted into this cavity during construction. Not wanting to disagree with what "Terra Ops" mentioned previously, but I personally believe this to be a considerable improvement, especially in colder climates. I also pitched them about a adding a second course of foam in the smaller space just behind where the two panels meet, something like either a low expansion spray foam or the poly foam rope used to fill cracks in log houses, both of which would be added during construction. That didn't happen for my build but I am sure they will be looking at it in the future.

As most folks know, "Thermal management" is also a lot about choices made during a build as well as, how you use the camper. Because I have a blank sheet of paper, I am trying very hard to make every design decision with it in mind. Sadly, I have already fallen with Tern windows but I couldn't help myself after falling in love with them after my last camper build!!!

 

[Terra Ops]

I'm always suspect when told someone has done something for XX number of years or they've XX years experience. The question is always have they been doing the same thing (production line) every month for XX years or have they done something (custom) different for every month for XX years.

There are other factors beside the width of the bond.

FRP is an insulator. Aluminum is the opposite and transfers heat/cold 300X faster than FRP.

R value of 2" Type II (worse if it's Type I) EPS is +/-R8
There has to be a vacuum (very few atoms) to stop conductive (not radiant) heat transfer. There is conductive heat transfer through (the atoms in) air which has an R value of +/-0.9.

Between the outside and inside corner looks to be 1.5" air gap so the corners are +/-R1.8 and the screws don't help.

View attachment 803245t

I'm always suspect when told someone has done something for XX number of years or they've XX years experience. The question is always have they been doing the same thing (production line) every month for XX years or have they done something (custom) different for every month for XX years.

I guess that can be said for anyone/anything when trying to give doubt.
As you point out, FR Plastic is not near as conductive as Aluminum. However, it is not inert. It still transmits temperature, unless there is a thermal break. A two-piece extrusion does just that. If the air gap is that much of a negative factor, the foam insert must help. As for the screws, they are removed after the interior bond is cured. I definitely think that pressure creates a stronger bond that just a slip in. Panels are not made without a force pushing them together. Such is the case for most applications. With a slip in extrusion, there is no pressure, only reliance on the glue.
While this has been engaging, I see you're a proponent of competitors. Peace man

 

[Terra Ops]

Alloy
I have one of first CPT campers, pretty much a prototype and I acted in part as a guinea pig in exchange for having a fair bit of input into my own design. I am very much still enjoying it and the continuing steep curve that occurs with interior self builds.

That being said, I would agree with a lot of what you have mentioned regarding the R value of the corners. The CPT units come from an industrial background (as you well know) and I was well aware of the potential around thermal shortcomings with their MTC units. I had discussions around this issue with CPT at the design phase and I was mostly instrumental in getting wire cut rigid foam profiles matching the large cavity, which were inserted into this cavity during construction. Not wanting to disagree with what "Terra Ops" mentioned previously, but I personally believe this to be a considerable improvement, especially in colder climates. I also pitched them about a adding a second course of foam in the smaller space just behind where the two panels meet, something like either a low expansion spray foam or the poly foam rope used to fill cracks in log houses, both of which would be added during construction. That didn't happen for my build but I am sure they will be looking at it in the future.

As most folks know, "Thermal management" is also a lot about choices made during a build as well as, how you use the camper. Because I have a blank sheet of paper, I am trying very hard to make every design decision with it in mind. Sadly, I have already fallen with Tern windows but I couldn't help myself after falling in love with them after my last camper build!!!

Nopec, what do you mean you have sadly fallen with Tern windows? I'm pretty sure they are rebranded Euro-vision imported from China. Not implying negativity, just saying.

 

[Alloy]

Alloy
I have one of first CPT campers, pretty much a prototype and I acted in part as a guinea pig in exchange for having a fair bit of input into my own design. I am very much still enjoying it and the continuing steep curve that occurs with interior self builds.

That being said, I would agree with a lot of what you have mentioned regarding the R value of the corners. The CPT units come from an industrial background (as you well know) and I was well aware of the potential around thermal shortcomings with their MTC units. I had discussions around this issue with CPT at the design phase and I was mostly instrumental in getting wire cut rigid foam profiles matching the large cavity, which were inserted into this cavity during construction. Not wanting to disagree with what "Terra Ops" mentioned previously, but I personally believe this to be a considerable improvement, especially in colder climates. I also pitched them about a adding a second course of foam in the smaller space just behind where the two panels meet, something like either a low expansion spray foam or the poly foam rope used to fill cracks in log houses, both of which would be added during construction. That didn't happen for my build but I am sure they will be looking at it in the future.

As most folks know, "Thermal management" is also a lot about choices made during a build as well as, how you use the camper. Because I have a blank sheet of paper, I am trying very hard to make every design decision with it in mind. Sadly, I have already fallen with Tern windows but I couldn't help myself after falling in love with them after my last camper build!!!

Foam inside the aluminum extrusion might gain 0.5R because the aluminum will still transfers cold around the foam. The best way to deal with condensation in the corners is to add a block of XPS on the inside an air seal it

It would make a better system if CPT allowed the panels to overlap. For this they could use a solid (no hollow spaces) extrusion that is less expensive to produce.

For the amont of extrusion needed and the time it takes the hollow section could be cut out to allow one of the panel to slide in further....or just use angle aluminum inside/outside

I won't use Tern windows/doors