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Old 04-06-2012, 03:37 PM   #1
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Insulation sandwich?

Hi all,

I have finally turned the corner in my shell-off! I'm finally done futzing with my frame and ready to start reassembly. The original construction of my trailer had the pink fiberglass insulation sandwiched between the frame rails and the plywood. I have heard varying opinions on this method, the pros being that it keeps the floor from squeaking when you walk on it, and the cons being that it wicks water up into the floor.

I was planning on using the reflective bubble wrap insulation on the underside of my floor--any opinions on whether to sandwich it between the frame and plywood?

I have also seen some posts where the rebuilder lays a thick bead of caulk or equivalent between the frame and plywood to keep the floor from squeaking. Would butyl tape be as effective, or would it just leave potential for a gap and mobility once the butyl squiches down?

Thanks in advance!
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Old 04-06-2012, 05:01 PM   #2
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I am headed to this decision myself, will be very interested in the responses to this thread.
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Old 04-07-2012, 09:19 AM   #3
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hey-yall-watch-this-shell-game <--- the path I followed. Only took 1,000 days daydreaming to commit to & execute it. You mileage may vary, restrictions and exclusions apply, snow may not be available at all locations, authors' past performance is no guarantee of future performance, not responsible for omissions or printing errors, professional on closed course so please do not try at home, adult supervision required, cash value 1/1000th of one cent, can not be used with any other promotion...

Lets look at some points, no disrespect meant if Joe Somewhen chose any/all of the following methods:

All the frame flange interfaces are rarely square - caulk-rubber tape will extrude & escape from inbetween them over time by just gentle shifting from occupants or traveling... leaving you with proud and loose screws. What could be done on a Bus or other rigid chassis frame does not apply on the supple Airstream frames.

About prodex as a gasket: The metal flanges are 3/4 to 1-1/4-inch wide and made of light gauge steel. The machine-thread screws (or nut/bolts) draw the metal up from any misalignment doing a flush-to-crush on the plywood. The foam may not resist the PSI exerted in the pinched-inch area but another inch away the resilient foam will be lifting the flooring, compressed around the floor bolts but bowing up the floor inbetween the fasteners. Maybe not day one, week one or even year one but over time it will happen, there's no 2x8 or 2x10 board load-bearing surface area as in home construction with mud & sill-plate foam, just that 3/4" wide steel spar.

Sheet foams' float provides friction reduction not helpful for floor-to-frame rigidity; example far corner to opposite corner of the 4'x 8' plywood sheets with 3/16" float-on-foam make that longest lever forever working directly on the sheet metal fasteners' threads or trying to topple the bolt columns as the 'live' traveling frame shimmery & waggle scene unfolds.

Looking at some star-wars-grade 3M 1/16" thick automotive double-sided adhesive tape you get the crush-down at the fasteners, bow up inbetween them but less lateral wiggle - but working with ultimate sticky tape would mean $15 worth of tape ruined every time you bobble the plywood alignment on install, and an hour trying to get the adhesive off to retry it. If the sheet is anchored-nested in one edge maybe a hinge-swing down, pulling the paper tape off the foam at the last minute and you'd have a tight floor with noise reduction and a degree of insulation. I chose not to do this since the foam can still hold water and it crushes & bows, and over $200 for the tape alone. The outrigger-floor interface could be mangled pretty fast from vibration and more than a few of my outriggers have a slope to them the thin foam tape would not bridge & fill.

>>> I've got errands and work, will continue posting later.
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Old 04-07-2012, 09:45 AM   #4
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Just my opinion - I would put nothing - having done a couple of resto's and getting ready to start another - I think all insulation does is trap moisture under the floor and here in NM I've camped in some very cold nights have never missed it -

Belly pans are not supposed to be sealed - they need to breathe...

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Old 04-08-2012, 06:26 AM   #5
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I agree with Ken J, I will also add that trapped moisture will bring on mildew and mold. I sealed all belly pan seams and added 4” round stainless steel vents to each floor cell to eliminate the moisture.


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Old 04-08-2012, 09:30 PM   #6
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The 'token expired' bug ate a nice post - I'll contribute again once I quit cussing the software tailor.

No clue why 'sealing' the belly was hoisted up the mast as its not part of OP's question or my response.

Quick picture of Prodex install I tore out for shell-off rehab...
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Old 04-12-2012, 06:51 PM   #7
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i'm pondering this at the moment myself, I have built a new frame and i have a gap between the board and the metal stringers which go between the main rails, what i've decided to do is to fill with a plastic strip, as for insulation it may get a layer of reflectix if it's lucky!
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Old 04-15-2012, 06:30 AM   #8
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I am thinking about just sealing the bottom of the plywood and painting a coat of silver reflective roof paint . we live in Florida.
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Old 04-15-2012, 10:24 AM   #9
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Quote:
I am thinking about just sealing the bottom of the plywood and painting a coat of silver reflective roof paint.. . We live in Florida.
I'd be afraid without ANY insulation when A/C pools the coldest air against the floor there would be condensation forming against the floor boards and spars, especially in Florida - It'd be like a glass of iced tea beading up on the outside when you're sitting out on the patio. With the belly-skins on, yes, it would be a finite amount of moisture but it would be happening. I've seen such dew lingering here from the shell interior & floor holding colder than outside air even without air-conditioning. I'd sure think some foam-board or Prodex closely fitted into the floor cavities would be a continuing payoff against battling dew-points if not for saving energy.

Quote:
I have built a new frame and i have a gap between the board and the metal stringers which go between the main rails, what i've decided to do is to fill with a plastic strip.. .
Wow, that is a wide open opportunity, remembering it hopefully is going to be forty or fifty years before there is a convenient opportunity to modify what seems easiest to do now. I've seen a dense & heavy plastic wood used to trim garage doors that if ripped into the correct thicknesses might provide good rigidity, weatherproofing and some insulation properties.

Any way - after seeing the dry-rot creep up the top of the ladder rails six and seven feet from wicked water in the pressed fiberglass, and the same thing happening on outriggers and huge pitting in the iron up front - nothing at all would be better than how the factory sabatouged our trailers just to have the 'hushed' floor for the "magic minute" when the units were being shown to customers. I like my floor with .065" silicone gasket locked in with 3M 5200 sealant but there has to be 1,000 ways to accomplish the same thing but the inert silicone has a chance to last 20+ years coupled with that blue-water marine grade sealant.
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Old 04-17-2012, 10:47 AM   #10
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Just in the interest of full disclosure - I noticed that I asked same thing last fall...

ProDex between new floor and frame? Comments?
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Old 04-17-2012, 01:52 PM   #11
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Originally Posted by Wabbiteer View Post
I like my floor with .065" silicone gasket locked in with 3M 5200 sealant but there has to be 1,000 ways to accomplish the same thing but the inert silicone has a chance to last 20+ years coupled with that blue-water marine grade sealant.
Wabbiteer, can you explain this a little further for those of us who are "simple"

Thanks,
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Old 04-17-2012, 03:35 PM   #12
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I would not use a radiation barrier material as a primary source of insulation. The stuff only works well when it is clean. It it sees moisture for long periods of time the aluminum will not be there very long. Also you want the stuff to be thermally floating if possible. That means nothing touching either side. As time goes by, the aluminum will get dirty and loose the ability to reflect heat. You would be better off with foam and then a layer of shiney stuff. Also as others has said you want water to be able to get out from between the layers. This was a BIG mistake Airstream made by putting the pink fiberglass over the frame members where it can hold water against the floor and frame. Leaving the floor unisulated might work in mild wet climates where water retention is more of an issue than R-value. I am not sure that the R-values of the plywood is much worse than that of the outter skins with a small layer fiberglass between them. The ribs are going to conduct heat between the skins like mad. I have debated leaving the floor without insulation so it can dry out but I will probably end up with some sort of insulation. Venting the skins is a real good idea in places like the east coast where it is raining or the humidity is high.

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Old 04-17-2012, 05:36 PM   #13
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Gee whiz Wally

I calculated 17.75 square foot metal-to-plywood contact area in the ladder frame & spars, outriggers and A-frame brace areas, for around 150 linear feet of gasket.

The silicone sheet, 0.065" thickness and stamped Boeing, was bought off ebay.

So i used the 3M 5200 marine sealant/adhesive to weld the silicone strips to the flooring and the metal, using the punched holes to act as rivets through the silicone since NOTHING will bond to it. So far so good, when warm weather returns I will pretty up the caulk lines, paint the underside with insulating paint and put something on it for real insulation... not sure yet
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