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Old 06-15-2011, 01:06 AM   #15
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I'm considering Rhino for the bottom of my end cap bellypans. While looking into it I discovered they have an eco-foam division that carries a lightweight spray in aluminized product with an R value of 6.8 per inch and creates a water barrier too. Fire rating is ANSI rated high. Hmmmmm.
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Old 06-15-2011, 10:35 AM   #16
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For the 3.476 time, closed-cell foam is not perfectly closed cell, 97 or 98% is the best they can do. Since Airstreams never leak and condensation is a non-issue maybe you should stop reading and jump to the smileys after this next text block...

The comparative foam volume of my trailer main shell at 16' by 18' with 1-1/2" thickness of foam would be 36 cubic feet. With 3% open cells that is one cubic foot, or 62 pounds, or 7-1/2 gallons of water storage possible.

If we count only the nearest tenth of foam thickness that is still 3/4 gallon of water holding capacity against the aluminum shell and spars. And that is only the beginning with unaged and unstressed foam, the cells continue to fail and moisture will capillary wick along random pathways throughout the total volume.

What we don't know about Avions can hurt us. The ALCOA OEM style protective plastic film that is so much fun to peel off new sheet metal would be a good start on having a spray foam protective barrier to keep water from undercutting and boring into the foam from any small defect, rivet or seam etc... IF the foam would chemically & physically bond and key into the surface.

I've seen water get underneath the factory Vulkem caulk schlabbered over the end cap interior seams to undercut its bond and run 16" from the leak and form a bladder holding water that squirted out like a clown flower when I was levering in the rear bath replacement floor. As gnarly as Vulkem is, time and freezing defeated it in a text-book worthy example.

I've also seen an old-guy in near-tears from sub-floor spray in foam that held enough moisture that the iron disappeared, leaving only an orange oxide stain. Looked like something you see on the banks of a polluted river, chunks of detritus randomized as he explored the damage once the plywood came out.

There had ought to be a law if you must foam it then you're obligated to keep the trailer for life, and store it carefully and do the maintenance.



A clean aluminum surface pretty much radiates zero infrared as a result of size and arrangement of its molecular surface. The @#*%^ spray adhesive used to adhere the OEM fiberglass in the shell hollows pretty much defeats that, and I don't know a good way to get the surface back to bare metal, can't get the 'clean' back once it's gone. Pressure washed degreasing and acid etched then passivation with an aircraft quality chromate treatment would be a good start and its not as difficult as it sounds, they are wipe on and rinse off treatments and a very good start to a forever trailer for countering the hidden weaknesses.

The question on a near perfect insulation is one that I've pondered more than a few hours on without fixating on the first shiny solution that appears... Right now I'm thinking its continuous Prodex (0.2") with a stand off from the shell by two layers (0.4") that is religiously tailored as a snug fit and perfectly foil taped to the ribs and C-channel... and then [drumroll please] anything you want to use, even (gasp) spray foam. The air gap and Prodex moisture barrier will allow liquid water to flow to the C-Channel if/when it occurs.

But that is not one I will use, just solving the spray in dilemma. I'll go with Prodex and pink housing foam bifold sheathing panels with a rib-to-liner thermal barrier of synthetic subroofing paper (not rubberized, just resin paper style)

Out of time, been away six weeks and a lot of catch up to accomplish...
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Old 06-15-2011, 11:28 AM   #17
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I am now of the opinion that any adhesive "thermal break" between the ribs and skin is the same as no thermal break. It provides a good contact surface to both sides and acts as a poor bridge to conduct heat.

The thing is, air is a free poor bridge.

Maybe, in this world of different poor solutions of varying cost, the thing is to look at ways of decoupling the inner skin from the air in the trailer so radiation and convection is reduced.

For the amount of time and money people spend trying to insulate their trailers to the Nth degree, I'm surprised by two things: that there are no after-market ribs designed to insulate, and that there are no products where the focus is to minimize contact area.

Yes, this is a change in my previous posted view that butyl tape is excellent - it's no better than a metal-air-metal contact.
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Old 06-15-2011, 12:40 PM   #18
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In response to the not 100% closed cell issue.

I agree on the exposed surface of closed cell foam there in not 100% closure.

However on the side of the foam that is in contact with the substrate material there is ( if applied correctly ) a near perfect closure. When you shoot foam under pressure at a substrate it forms a fluid bed and then expands outward. If the substrate will have any mechanical sheer ( two riveted panels) there is some benefit in spraying a latex elastomer first.
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Old 06-15-2011, 02:07 PM   #19
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any adhesive "thermal break" between the ribs and skin is the same as no thermal break
If true then all the home energy-saver window frames sold have ineffective thermal barriers between inner & outer frame stampings. You said yourself that "Aluminum K factor is 250.00" so anything to reduce that hundred-fold is a worthy endeavor, even if it is a layer of kitchen counter-top formica or brown paper grocery bag glued on the ribs with 3M spray contact adhesive.

When considering any laminate inbetween ribs and inner shell 'liners' note the semi-monocoque shell strength depends on near zero movement between each bonding point, when we get movement we see sheared pop-rivets.

An air gap between inner liners and the ribs would introduce some flex when it was engineered to have interference through lying flush parallel to the ribs for stiffness.

The barrier strip should have no/low compressibility that would increase with vibrations causing the pop-rivets to loosen. I've read here that new Airstream outer shells have seam tape applied with double-sided ultimate adhesive that is then buck-riveted - the tape alone almost holds the unit together, the seam tape compressibility is calculated against rivet crush force and the deformation limits of the sheet metal and is a straightforward assembly process. If you wanted to make say 1mm inner-rib stand-offs and MIG weld them to the ribs AT EVERY POP-RIVET you could lay up a 1mm silicone thermal barrier everywhere else along the rib and eliminate 99% of the metal contact area, retain mechanical strength with no air gaps, and importantly not deform the inner liners 'flatness' where it compresses at each pop-rivet. But fabricating and bonding the 1200 or more stand-offs would drive one barking mad in short order.

I've wondered if adding a second liner false ceiling of 0.024" 2024 isolated by 3/4" from the 1970's ceiling and upper wall would solve 80% of the hot/cold intrusion (winter heat loss and summer sun loading). I've read here the new Airstreams have 3-inch walls, maybe cross furring with 1/2" box beam aluminum stringers inside the original liners panels is possible.

Whatever, its all academic on my end - I'll just be lucky to get the project back together
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Old 06-15-2011, 05:09 PM   #20
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A nice cardigan sweater in wool works great!
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Old 06-15-2011, 05:22 PM   #21
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There is a mixing of applications in this thread. I prefer to keep things "Sesame Street simple"...there are two distinct principles of physics being debated:

Heat transference or conductivity
And
Insulative properties

Two distintly different principles, yet oddly entwined.

Think about aluminum foil: shiny side reflects (heat transference/conductive property)
Dull side absorbs heat (insulative property)
How you use it depends on your objective.
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Old 06-15-2011, 09:43 PM   #22
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Not to throw another witch on the fire, but I have used this product for insulating shipping containers.

It has a K value of 0.07 and can be sprayed on under insulation.

It may be worth a test of specifically spraying the face of the ribs with a few coats before replacing the interior skins.

Multi-Ceramics Insulation

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Old 06-16-2011, 04:12 PM   #23
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Originally Posted by Darkspeed View Post
Not to throw another witch on the fire, but I have used this product for insulating shipping containers.

It has a K value of 0.07 and can be sprayed on under insulation.

It may be worth a test of specifically spraying the face of the ribs with a few coats before replacing the interior skins.

Multi-Ceramics Insulation

I have friends building ICF ( insulated concrete form) homes in the Dallas area and they are using a ceramic coating in place of the normal polymer sand stucco. It is a great product.
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Old 06-16-2011, 04:40 PM   #24
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Originally Posted by Phrunes View Post
There is a mixing of applications in this thread. I prefer to keep things "Sesame Street simple"...there are two distinct principles of physics being debated:

Heat transference or conductivity
And
Insulative properties

Two distintly different principles, yet oddly entwined.

Think about aluminum foil: shiny side reflects (heat transference/conductive property)
Dull side absorbs heat (insulative property)
How you use it depends on your objective.
There is another important factor being Air infiltration and even air movement inside the wall and floor cavity itself.
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Old 06-16-2011, 04:55 PM   #25
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Context is key...

Quote:
Originally Posted by Phrunes View Post
A nice cardigan sweater in wool works great!
Yes, well... at the moment it's 101F here, I don't think a sweater is going to help much with THAT.
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Old 06-17-2011, 12:27 AM   #26
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Originally Posted by DKB_SATX

Yes, well... at the moment it's 101F here, I don't think a sweater is going to help much with THAT.
A wet cardigan maybe? :-)
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