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Old 11-11-2015, 03:43 PM   #183
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Spray Foam Insulation

My 1969 Ambassador has/had spray foam on the underbelly. It appears to have been "open cell" since the places that got wet stayed wet and held moisture against the frame. The sections of the frame that were dry and coated with foam stayed in perfect condition. Overall, the 40+ year old spray foam is a pain to remove, and the powder that comes off it burns your eyes. Add to the years of mice that have been tunneling and nesting in it.. Pulling down all that nasty old spray foam really turned me off to using it again.

I'm sure modern spray foam is much better, and there is some designed for over the road use. Let us know what you go with and please post pics of the finished job!
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Old 11-11-2015, 04:25 PM   #184
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One thing that is seldom mentioned about spray foam..... It burns quite aggressively.

https://foursevenfive.com/reason-foa...e-fire-hazard/

Brevi tempore!

Even the cheap stuff in a can at HD/Lowes comes in a Fire Retardant flavor now (made specifically to STOP fire). I would assume insulation for home and auto is fire retardant (although one should obviously check before covering the entire inside of their AS with it!).
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Old 11-11-2015, 04:27 PM   #185
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Originally Posted by Silverflames View Post
My 1969 Ambassador has/had spray foam on the underbelly. It appears to have been "open cell" since the places that got wet stayed wet and held moisture against the frame. The sections of the frame that were dry and coated with foam stayed in perfect condition. Overall, the 40+ year old spray foam is a pain to remove, and the powder that comes off it burns your eyes. Add to the years of mice that have been tunneling and nesting in it.. Pulling down all that nasty old spray foam really turned me off to using it again.

I'm sure modern spray foam is much better, and there is some designed for over the road use. Let us know what you go with and please post pics of the finished job!
Yeah... I think spray foam is a bad idea for the underside (water can pool on TOP of it). If there are mice in it and it's absorbing water, it's most likely open cell and not good for this application. Even if someone chooses spray foam for the walls, I would definitely recommend PIC (polyisocyanurate) panels for the underside.
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Old 11-12-2015, 12:21 AM   #186
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Polyiso is great but NOT underneath!

We frequently use polyisosyanurate foam in our new custom Airstream builds and vintage rebuilds for its superior qualities. However, we do not use it under the floor. It was a propensity to absorb water in that application and cannot readily dry. We use polystyrene under the deck.
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Old 11-12-2015, 01:10 AM   #187
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Spray Foam Insulation

Building codes almost uniformly require a heat barrier like 1/2 " drywall or stucco encapsulation be used over foam insulation whether it is of the fire retardant variety or not.

Do I think that codes are often over the top and nonsensical sometimes?

Absolutely.

I would have to study over this a bit before I committed to foam if I was going to consider it again. From where I stand, the good old fashioned fiberglass worked so well in my trailer that I would have a hard time justifying the trouble and expense of spray foam on my next project.




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Old 11-12-2015, 12:10 PM   #188
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We frequently use polyisosyanurate foam in our new custom Airstream builds and vintage rebuilds for its superior qualities. However, we do not use it under the floor. It was a propensity to absorb water in that application and cannot readily dry. We use polystyrene under the deck.
Thanks for the response, Brett, and good to know about the PIC under the deck (which is what I erroneously thought it was best for). My exploration of PIC actually began with an article quoting Timeless Travel Trailers and their work on a Spartan. Then I saw more from you here on the forums, and it greatly influenced my decision to switch from Spray Foam to PolyIso panels.

Good to know that the PIC actually absorbs water even though it is marketed as:
  • "Superior resistance to moisture and vapor in above grade applications"
I assume the polystyrene you are talking about for under the deck is the stuff next to the PIC on the shelves at Lowe's marked XPF (Expanded Polystyrene Foam)?

Are you using the PIC in the walls (vs. using the expanded polystyrene there as well) because of the gain in R value (PIC=R6 per inch and Polystyrene=R5 per inch)? Wondering if the difficulty with moisture is worth the single R value digit.

Thanks again.
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Old 11-13-2015, 12:01 AM   #189
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The PIC we use has a foil face on each side and has an R-Value of 7 per inch amounting to R=9.6 for 1 3/8" thickness. We also seal all joints with foil tape to form a moisture barrier. Under the deck we us extruded polystyrene for an R value of 5 per inch. The expanded foam is much more of a nuisance to cut and install leaving thousands of little white beads to infest the work space even with a good dust collection system. It is also has only an R-4 rating.


(Good choice of tow vehicle!)
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Old 11-13-2015, 05:02 PM   #190
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The PIC we use has a foil face on each side and has an R-Value of 7 per inch amounting to R=9.6 for 1 3/8" thickness. We also seal all joints with foil tape to form a moisture barrier. Under the deck we us extruded polystyrene for an R value of 5 per inch. The expanded foam is much more of a nuisance to cut and install leaving thousands of little white beads to infest the work space even with a good dust collection system. It is also has only an R-4 rating.


(Good choice of tow vehicle!)
Thanks for the specifics, Brett!

And yeah... I love the CRD... so much that we bought another one! I was getting nearly 20mpg at around 65mph on the way home from the Midwest. Granted, the Airstream is currently gutted, but it was full of lots of the stuff that will be installed (toilet, tanks, water heater, electrical components, tools, etc.), so I'm pretty happy!
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Old 11-16-2015, 04:39 PM   #191
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Insulation with any kind of panel means having to cut it exactly to fill the space and then sealing the edges with spray foam or tape or both. Insulation failure is mostly related to not sealing it well. Professionals using fiberglass batts were found to leave many air spaces and the nominal R value was reduced by as much as a third by not very professional work. The rigidity of panels makes it difficult to use them, especially in a trailer with curved walls, but it can be done.

I'm not about to tear my trailer apart, but if I did, I'd look into spray foam. The OEM fiberglass can only provide an R value of 4 or so at best. If you are familiar with Airstream workmanship, it is safe to assume the insulation is poorly installed and provides little help (new hires traditionally were, and still may be, given insulation as their first job at the factory). And they don't used thermal breaks between the skins and the frame. You should. I'm unsure just what would work in a trailer, but even a thin slice of rigid foam would help.

The spray cans at the big box stores are tricky to use. Be sure to get the stuff that expands the least because even that will surprise you when it expands. I think it is the stuff that says for doors and windows. You can cut it with a kitchen knife once it dries. And you have to clean the tube immediately or it is very hard to get the foam out and you end up throwing out a partially used can.

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Old 11-16-2015, 06:09 PM   #192
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And they don't used thermal breaks between the skins and the frame. You should. I'm unsure just what would work in a trailer, but even a thin slice of rigid foam would help.
Gene
I've wondered about the effect of installing a thermal break on the structural integrity of the trailer. It seems to me that adding a non-rigid layer between the interior skins and the ribs would put more stress on the blind rivets because they're no longer clamping the two pieces of aluminum directly together. The interior skins would be able to move slightly as the trailer flexes and over time that might lead to the rivets loosening.

Not sure that this would be a problem, just wondering.

Perhaps some sort of double-sided tape would prevent the movement between the skin and the ribs, but I think it would be hard to get the skin in exactly the right place before it stuck. And what if you needed to remove the panel later?
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Old 11-16-2015, 06:52 PM   #193
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Spray Foam Insulation

If our AS ever gets gutted, the joints will be slathered in Trempro, the wiring will be in conduit, the outer skin will receive a layer of Reflectix glued and taped between ribs, and the higest density spray foam available applied with another layer of Reflectix on top before the inner skins go back on.
The belly will receive a similar treatment after the tank heating pads are installed on the bottom side of the tanks and the banana wraps will be tucked under the wall skin.
An Eva-Dry 2200 dehumidifier will be our traveling companion.
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Old 11-16-2015, 07:23 PM   #194
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I've wondered about the effect of installing a thermal break on the structural integrity of the trailer. It seems to me that adding a non-rigid layer between the interior skins and the ribs would put more stress on the blind rivets because they're no longer clamping the two pieces of aluminum directly together. The interior skins would be able to move slightly as the trailer flexes and over time that might lead to the rivets loosening.



Not sure that this would be a problem, just wondering.



Perhaps some sort of double-sided tape would prevent the movement between the skin and the ribs, but I think it would be hard to get the skin in exactly the right place before it stuck. And what if you needed to remove the panel later?

I was thinking the rubber roof flashing might be a good option on the inside ribs. It's sticky on one side, and is a little flexible. It could limit some of the heat transfer from the inside to outside skins. Any thoughts?
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Old 12-12-2015, 02:13 PM   #195
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Well, I've made my decisions, and I'm backing them with action. I've taken the plunge and I'm going with Polyisocyanurate. It's $16 a 4x8 sheet for one inch thick Rmax Thermasheath-3 at the local Home Depot (2" is $30 and 1/2" is $12). This means it's readily available and I can do sections at a time (for the spray foam to make sense, it would require doing everything at once). The panels are UNBELIEVABLY light. 2" is too thick for the ribs, so that was out. 1" is actually the "sweet spot" in pricing, so that's what I'm using for the bulk of the material. I bought a sheet of 1/2" that I'm using for spacers, so I cut that sheet and glue 1" by 3 or 4" pieces of the 1/2" thick stuff to the exterior skin using some old silicone adhesive I had lying around, then I lay the 1" thick stuff over that (scoring the back for curves and then resealing the score with foil tape). This means I've got a 1/2" air gap against the skin, then 1" of R-6 polyiso with a foil vapor barrier on both sides, then another approximately 1/4" air gap between the polyiso panel and inner skin. All seems between panels get sealed up with foil tape.

The air gap on either side of the 1" panel not only helps with insulating, but it also means I can run wire if I need to.

To test the moisture resistance of the polyiso, I soaked a piece in water for a week, and it didn't seem to deteriorate or take on water. I'm getting a little more scientific with the experiment by weighing three pieces of the polyiso, submerging them in water, and I'll weigh them again in a couple of weeks to see if there is any moisture in each piece.

I'm still not sure what I'll be using for a thermal break on the ribs (foam tape, poly foam roll, EPDM rubber), but I have to decide soon, as I want to get the end shell up by end of the weekend.

p.s. It's snowing and f-f-f-f-freezing in the trailer! Can't wait to get this stuff finished!
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Old 12-29-2015, 05:20 PM   #196
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Same idea!

How has it worked kidjedi? After a ton of research, I'm about 3 weeks behind you, but making the same decisions. I'd love to know if it's working out!
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