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Old 06-15-2013, 11:15 AM   #225
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I've got a letter into sales at PolymerSheet.com asking about recommendations on .020 to .0625" sheet polymers..

High Density Polyethylene
Ultra High Molecular Weight Polyethylene
Low Density Polyethylene
Polypropylene
etc..
Sales department replied at ten minutes till 5pm Friday with 'Can't help, our thin PE products are not UV resistant'. My response, written without insult explaining where they missed intelligence, has been sent.

Thin sheet UHMWPE, HDPE, PE or Polypropylene has ~1/400th the heat conduction of aluminum, the outer shell will get proportionately hotter without inner liners sinking away heat yet higher temps enjoy greater convection & radiative cooling, things still balance out with a cooler interior.

A product example - smooth surface 1/16" 4' X 8' (0.0625") HDPE is $52 a sheet and will produce 380' feet of 1" gasket. A nearby metal shop that can shear the 48 strips would remove some of the tedium of that chore...

Now how to stick the PE to the ribs long enough to get liners installed...
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Old 06-16-2013, 07:35 AM   #226
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I'm wondering about using this elastomeric ceramic microsphere paint as a thermal break on the ribs. One gallon would be plenty at $32 I could actually afford it. http://www.hytechsales.com/prod1000.html
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Old 06-16-2013, 09:32 PM   #227
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Finishing up the insulation.


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Old 06-17-2013, 10:41 AM   #228
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Man, I wish I was as far a long as you! But thanks for sharing. It will help me get through...

check out this layout below and give me your thoughts.

I haven't seen a layout with the kitchen in front and wonder if there is a reason to NOT do this.

This layout is for my 22' Cloud but I will apply this layout for both trailers.
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Old 06-17-2013, 08:14 PM   #229
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EDIT - looking at the photos I can't see any ribs left exposed! How about painting the insides of the liners?
-----
Timzog: I am sad I can't say "THIS WORKED" and glad I haven't committed to any one process yet.

I could see three coats of the elastomeric paint on the ribs. I bought the hytech aluminum radiant barrier paint w/ beads - and I bought the bulk pack of raw beads. Plan *was* to use a bonding paint, the radiant paint and both with beads, then choose insulation. As it stands now, will allodine treat the shell interior and pop $750 for spray foam, 400-600 sqft at 1 inch coverage for R7+...

The insulating beads depend on a thin bodied carrier to draw the beads into a tightly packed layer like little stacked cannonballs for the idea to work - ideal would be a light bodied lacquer, blah blah, or POR-15 .

I'll send you some raw beads if'n you treat the aluminum rib faces with a bonding process like the POR zinc process, it leaves zinc whiskers for paint to bite to, and would be a forever rib face coat. Might you have any POR-15 laying around?

For the shell sheet metal I have a whim to try a harbor freight powder-coat paint duster to fog an even EXTRA layer of the beads on wet paint surfaces - the beads are small and light but I don't know if they are 'light enough' to dust evenly, or at all. The HF unit has a high voltage static field generator built in so the fog of dust should* lay up by static attraction into an even coating.

Polymer Joe replied their stuff will take the heat, and the mechanical binding but noted it does swell and contract with temperature changes. My notes say HDPE expansion is 0.000059 to 0.000110 inch per inch per degree C, or a maximum 0.000006875" per degree C for a 1/16" sheet so a 60°C swing (above installation temp of 24C°) would be 0.0004125" heave against the pop-rivets and entirely acceptable as the pop-rivets will too be expanding from the heat.
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Old 06-18-2013, 08:21 PM   #230
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Originally Posted by rowdyATX View Post
Man, I wish I was as far a long as you! But thanks for sharing. It will help me get through...

check out this layout below and give me your thoughts.

I haven't seen a layout with the kitchen in front and wonder if there is a reason to NOT do this.

This layout is for my 22' Cloud but I will apply this layout for both trailers.
Your layout looks cool. The big concern with a front kitchen is how to drain the sink. I can't see where you'd put the grey tank to get a 1/4" per foot slope and still keep the pipes from hanging too low.
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Old 06-18-2013, 08:34 PM   #231
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EDIT - looking at the photos I can't see any ribs left exposed! How about painting the insides of the liners?
-----
Timzog: I am sad I can't say "THIS WORKED" and glad I haven't committed to any one process yet.

I could see three coats of the elastomeric paint on the ribs. I bought the hytech aluminum radiant barrier paint w/ beads - and I bought the bulk pack of raw beads. Plan *was* to use a bonding paint, the radiant paint and both with beads, then choose insulation. As it stands now, will allodine treat the shell interior and pop $750 for spray foam, 400-600 sqft at 1 inch coverage for R7+...

The insulating beads depend on a thin bodied carrier to draw the beads into a tightly packed layer like little stacked cannonballs for the idea to work - ideal would be a light bodied lacquer, blah blah, or POR-15 .

I'll send you some raw beads if'n you treat the aluminum rib faces with a bonding process like the POR zinc process, it leaves zinc whiskers for paint to bite to, and would be a forever rib face coat. Might you have any POR-15 laying around?

For the shell sheet metal I have a whim to try a harbor freight powder-coat paint duster to fog an even EXTRA layer of the beads on wet paint surfaces - the beads are small and light but I don't know if they are 'light enough' to dust evenly, or at all. The HF unit has a high voltage static field generator built in so the fog of dust should* lay up by static attraction into an even coating.

Polymer Joe replied their stuff will take the heat, and the mechanical binding but noted it does swell and contract with temperature changes. My notes say HDPE expansion is 0.000059 to 0.000110 inch per inch per degree C, or a maximum 0.000006875" per degree C for a 1/16" sheet so a 60°C swing (above installation temp of 24C°) would be 0.0004125" heave against the pop-rivets and entirely acceptable as the pop-rivets will too be expanding from the heat.
Thanks Wabbiteer,
I have aluminum foil tape covering all the ribs now, yes. I am glad to have your info, as always. It would seem that the key would be to maximize the ratio of the volume of beads to the volume of paint/ binder. If the binder (aka paint) particle size is much smaller than the beads, you could calculate the spaces left over in close packed spheres to determine a ratio that would result in the stacked cannonball structure with some binder to hold it all together. I was looking at the ratios in the premixed paints and they are low which would mean that the insulating properties would be similar to the paint, if I am following you correctly. I think some experiments are in order. If you could spare me some beads, I'd be willing to try a couple tests.
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Old 06-19-2013, 04:53 PM   #232
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They really push using spray equipment to increase the likelihood of even layers.

And yes, for you I'll open the 5qt bag, and instantly have microspheres covering everything including the cats! Beware what you ask for

The term 'elastomeric' is deceiving as any laytex outdoor house paint is designed to be flexible, just some more than others.

I'm thinking the best place for the beads is the exterior roof final top-coat to stall any metal from heating in the first place?
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Old 06-19-2013, 10:22 PM   #233
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They really push using spray equipment to increase the likelihood of even layers.

And yes, for you I'll open the 5qt bag, and instantly have microspheres covering everything including the cats! Beware what you ask for

The term 'elastomeric' is deceiving as any laytex outdoor house paint is designed to be flexible, just some more than others.

I'm thinking the best place for the beads is the exterior roof final top-coat to stall any metal from heating in the first place?
Thanks dude! I've made my own down sleeping bag before and if these things spread around the room like down, I'm afraid!
I will try a few different kinds of paint with beads on my ribs and see if I can detect a difference.

The most volume that can be occupied by spheres is 74%. https://en.wikipedia.org/wiki/Close-..._equal_spheres

I wonder if a paint could be mixed at 3/4 beads and 1/4 paint.
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Old 06-19-2013, 10:52 PM   #234
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I have a Frostline 3lb mummy kit bag that's been most everywhere North of Key West (try staying warm w/ 9th degree sunburn)...

Here, note the gratuitously borrowed hytech diagram doesn't claim uniform beads. And these are tough but I kind of doubt a 74% bead coating would survive pop-riveted clamping over 1000's of night since thinned paint resins might allow too much bead-to-bead contact and fracturing-abrasion-voids develop...
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Old 06-25-2013, 08:55 PM   #235
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Still thinking about thermal break material. Another option could be a 1/16" fiberglass tape. I worry about the mechanical properties, but maybe 1/16 is thin enough?

http://www.firesleeveandtape.com/AB-...g-T-FG-W-P.pdf
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Old 06-27-2013, 11:49 PM   #236
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I think I may have found a thermal break material. I found it at Home Depot. It was $5 for a 50 ft roll. It is PVC pipe wrap tape. 2" x 20 mil, which is 1/50th of an inch. The thermal properties are pretty good. I am thinking that two layers might do at least some of the work in breaking the heat transfer between the aluminum. I've tried to learn about thermal breaks and it is different than R factor, but I haven't found a way to quantify that so I really have no idea how thick to make this thing. I'm going to test it in the UT sun tomorrow and see what happens.


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Old 07-01-2013, 01:56 PM   #237
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I think I may have found a thermal break material. I found it at Home Depot. It was $5 for a 50 ft roll. It is PVC pipe wrap tape. 2" x 20 mil, which is 1/50th of an inch. The thermal properties are pretty good. I am thinking that two layers might do at least some of the work in breaking the heat transfer between the aluminum. I've tried to learn about thermal breaks and it is different than R factor, but I haven't found a way to quantify that so I really have no idea how thick to make this thing. I'm going to test it in the UT sun tomorrow and see what happens.


I would tell you all about the amazing differential equations of heat transfer that I have, and provide you with a copy of a great textbook on momentum, heat, and mass transfer, fluid mechanics, and thermodynamics, but in the end, the only thing that matters is your real life experimental results. You have truly awakened the scientific side of my brain to this question, because I realized that my job's FLIR thermal imaging camera would be great for understanding the differences in temperature of the shell at various points with this stuff applied. It would be able to tell us the variations in temperature with better than 0.1 deg F accuracy and 320x240 resolution. We could set up side-by-side comparisons along the length of the trailer. So, wanna make a road trip to So Cal?

I really hope you get some good results, because otherwise when I find my next Airstream renovation in a few years, I'll find myself setting up an adult science fair project on this.

The biggest concern I have is how you insulate the rivets to prevent them from simply transferring most of the heat through. I know they are small compared to the rib-to-shell contact surface area, but they are still direct metal connections nonetheless. Also, how much air flow or cooling effect are you going to have on the interior? Are we talking about just delaying the inevitable temperature rise, or are we trying to minimize the heat transfer between a forced-cooled interior and the sweltering exterior?
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Old 07-01-2013, 08:57 PM   #238
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General Zog... I failed to bag up a sample and send it, I'll try to get on that tomarrow. Apologies.

Including window frames about 475 feet of rib & stiffeners in my 27' need to be finessed with thermal breaks. The true ribs hold about 1.75 sqft of contact area and figuring the pop-rivets at one per linear foot on the ribs equals 0.22 sqft of aluminum conductor. The stiffener - stand offs are larger, say 1.95 sqft. So, after a thermal break is installed the pop-rivets are less that 6% of the previous untreated area.

Remember we're not looking for R-1, just better than the R-0 that exists as is.

A Heat Transfer Textbook, 4/e
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