rruff
Explorer
The foam needs to go in that triangular spot, not inside the extrusion.
It would be easier and probably better to just cut the edge of one of the panels to fill that void. Slap some glue on that interface while yer at it...
DIY Composite Flatbed Camper Build
- Thread starter Terra Ops
- Start date
It would be easier and probably better to just cut the edge of one of the panels to fill that void. Slap some glue on that interface while yer at it...
NOPEC
Well-known member
JeffNopec, 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.
That wasn't very clear.... They definitely are Euro-vision, says right on them. What I was trying to say
was that despite my comment about camper design and planning, I still picked a product (AT windows) solely based on liking them, not whether or not they had superb thermal qualities. But I guess, it can't just be all about performance.....
Alloy
Well-known member
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
There's no need for FRP with a thermal break because the thermal break material transfers more heat than the FRP.
Pressure joint is marketing BS. It like saying welding is stronger than bolting. The bond strength goes to the one with the greater surface area but it's 1 of many factors that affects durability.
Well I'm trying to understand the marketing BS comment. If you have two equal applications with same surface area, one is slip in with no pressure and the other is, which is stronger?
Also an update on the corners; they are now filled. See attached. Also you mentioned not using Tern window/door. May I ask why? They seem very popular and well liked.
Attachments
NOPEC
Well-known member
I don't have any experience with AT doors but this is the second build in which I have used Tern windows. I really like them but others tend to pu-pu them, I think mostly because of their aluminium frames. There maybe better stuff out there but for me, these are just great. (my previous comment about "falling by using Tern windows", was tongue in cheek but sadly, only I got the joke...")
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I've had good results bonding with epoxy to anodized surfaces. With raw aluminum I've sandblasted and sprayed zinc chromate as a primer for epoxy.Technically aluminum should be primed prior to any paint, sealant, or adhesive.
In my experience, Acid#8 by Upol does a great job. Have yet to have a failure of any kind since using it.
Sand out aluminum, prime, then proceed.
National Rule ACID#8 Acid Etch Primer - U-Pol
1K ready to spray phosphoric acid ester formula promotes paint adhesion to difficult substrates, like galvanized steel and aluminum.u-pol.com
rruff
Explorer
Sorry but they are wasting their time with that. Aluminum has extremely high thermal conductivity, so on the external extrusion the outer aluminum wall and inner aluminum wall will be the same temperature. The insulation needs to be in that triangular space where the two panels meet. Or like I said earlier, I think it would be best to just cut the edge of one of the panels to fill that space. It still won't be a "perfect" thermal break, but more than adequate IMO... and stronger as well, if additional adhesive is applied to that interface.
Alloy
Well-known member
Which one is weaker/stronger depends on how it is assembled.
- Slip together suffers from scraping the adhesives from one/both sides of bonded surface so the parts have to be kept straight/parallel during assembly.
- If the screws exert too much pressure all of the adhesive is squeezed out. The screws should only be snugged up.
Filling the extrusion with foam is pointless as the aluminum transfers heat 300X around the insulation
Initially water/condensation pours off aluminum frames. As the temp drops ice forms which freezes windows and door shut so you're trapped inside. When the ice melts off the frames there are pools of water to mop up.
I'll try to address all these interesting observations and opinions.
Let's start with the picture cross section. First it is incomplete. The panels for camper applications are foam core. The picture shows the first step application bonding the outer extrusion. When cured, the second step is to remove the screws and apply adhesive in the corner of the inner extrusion. Then re screw to form consistent bond and strength. Final step is to remove the screws once cured so there is no direct thermal bridge. Alloy said 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. That has been addressed, but as Ruff points out it may not be enough. However, as I just explained, by filling the inner "triangle" with sikaflex, this should help reduce the transfer.
Here are some responses directly from the manufacturer.
The aluminum extrusions need to be coated with something prior to bonding. Normally for us this is powder coating. If you are wanting bare metal extrusions, there is a primer that can be put on the bonding area.
We use a Type 2 EPS foam. The foam itself has an R value of 4.75 per inch. The R value of the skins themselves is 0.25. So on a 1.5” thick panel the R value is 7.38. A 2” thick panel would be 9.75. Others may claim a much higher R value, higher than the combined totals of their material, because they "somehow" tested the panels. This is not how R value works. There is another measurement that can be used to calculate what they may be trying to claim, but that number would not mean anything to anyone.
The adhesive is SIKA 252. This is a very common commercial and automatic transportation adhesive. We built over 50,000 sleepers with this same adhesive, which was tested and specified by Daimler Chrysler, without a single adhesive failure.
The image they are seeing with the panels bonded up needs to be updated with insulated panels, and a foam insulator that we put in the extrusion to fill the air gap.
The slip in method of bonding can work. There are various companies that use this. However, with this method you are relying on the correct amount of adhesive being applied, and the panel being inserted correctly so that adhesive is not wiped away, and that there is adhesive contact everywhere. It is certainly possible to do this. With the clamping method, we can control where the adhesive is applied, and that we have a proper bond line. With clamping together, the adhesive is designed to squeeze out as it is clamped. We can physically see that adhesive has been applied along the whole bond line.
The FRP extrusion is a good extrusion. We choose not to use that method for the reasons above. We have a proven track record of using it. The clamp method for bonding is something that Daimler uses on all bond surfaces for the sleepers we built. In any redesign paths they always rejected/stayed away from slip in bonding. They didn’t use it as marketing, they just tested and designed.
The comment about overlapping panels would be better, is absolutely valid. It would probably make for a more insulated panel. We have to install other pieces to combat this. The rounded look that we have is achieved by the way we assemble the units together.
Let's start with the picture cross section. First it is incomplete. The panels for camper applications are foam core. The picture shows the first step application bonding the outer extrusion. When cured, the second step is to remove the screws and apply adhesive in the corner of the inner extrusion. Then re screw to form consistent bond and strength. Final step is to remove the screws once cured so there is no direct thermal bridge. Alloy said 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. That has been addressed, but as Ruff points out it may not be enough. However, as I just explained, by filling the inner "triangle" with sikaflex, this should help reduce the transfer.
Here are some responses directly from the manufacturer.
The aluminum extrusions need to be coated with something prior to bonding. Normally for us this is powder coating. If you are wanting bare metal extrusions, there is a primer that can be put on the bonding area.
We use a Type 2 EPS foam. The foam itself has an R value of 4.75 per inch. The R value of the skins themselves is 0.25. So on a 1.5” thick panel the R value is 7.38. A 2” thick panel would be 9.75. Others may claim a much higher R value, higher than the combined totals of their material, because they "somehow" tested the panels. This is not how R value works. There is another measurement that can be used to calculate what they may be trying to claim, but that number would not mean anything to anyone.
The adhesive is SIKA 252. This is a very common commercial and automatic transportation adhesive. We built over 50,000 sleepers with this same adhesive, which was tested and specified by Daimler Chrysler, without a single adhesive failure.
The image they are seeing with the panels bonded up needs to be updated with insulated panels, and a foam insulator that we put in the extrusion to fill the air gap.
The slip in method of bonding can work. There are various companies that use this. However, with this method you are relying on the correct amount of adhesive being applied, and the panel being inserted correctly so that adhesive is not wiped away, and that there is adhesive contact everywhere. It is certainly possible to do this. With the clamping method, we can control where the adhesive is applied, and that we have a proper bond line. With clamping together, the adhesive is designed to squeeze out as it is clamped. We can physically see that adhesive has been applied along the whole bond line.
The FRP extrusion is a good extrusion. We choose not to use that method for the reasons above. We have a proven track record of using it. The clamp method for bonding is something that Daimler uses on all bond surfaces for the sleepers we built. In any redesign paths they always rejected/stayed away from slip in bonding. They didn’t use it as marketing, they just tested and designed.
The comment about overlapping panels would be better, is absolutely valid. It would probably make for a more insulated panel. We have to install other pieces to combat this. The rounded look that we have is achieved by the way we assemble the units together.
No worries, I get it now
Are you posting progress of your build?
rruff
Explorer
That is very weak foam if this is what they are talking about... https://www.insulfoam.com/wp-content/uploads/2014/04/13005-Below-Grade-Type-II-TDS_WEB_8-16.pdf
Alloy
Well-known member
Type II EPS is good because the foam has little to do with the overall strength.
rruff
Explorer
There is a huge difference between say 4 lb PVC and 1.5 lb EPS... in strength and stiffness. Impact, compression, shear. If the core fails, the whole panel fails. In my testing the PVC foam was a lot better than 25 psi XPS, which should be stronger and stiffer than type II EPS.
They mention PVC foam on their site. I'd ask about that.
Alloy
Well-known member
Sorry I should have said foam has little to do with the overall strength needed for a habitat. There is no impact loading like a boat has.
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