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Old 01-04-2011, 01:14 PM   #15
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Indeed. Two layers will be at most 1.32 times as effective as one layer.

You'll get a far better result by using butyl tape to insulate the inner skin from the ribs as best you can. The rinse are neat little fins that equalize the inner and outer skin temp wherever they can. The ribs are very effective heat pipes without butyl tape.
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Old 01-04-2011, 01:47 PM   #16
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I'm in the process of doing mine with Prodex right now. I agree "the stuff is a joy to work with". I agree with Chris though, I went with Prodex for it's effectiveness, not so cozy as a home for vermin, and it would not absorb water. I am doing two layers with an airspace between the shell, the layers and the inside skin.
Hi SilverHoot;
Prior to insulating my 26' Argosy i have done plenty of research. Final decision was made to use Prodex with special installation technique. In the walls I have glued 5/8" low grade urethane strips on the inside of outer skin next to ribs with one strip in the center running vertically. Each and every horizontal strip was cut 1/8" short of vertical strips to allow moisture to drain all the way down. Prodex was cut to panels 2" larger on each edge. Panels were glued to the urethane strips and the side of the ribs. After glue was dry the excess Prodex was trimmed 1/16" past the surface of the rib. My wiring was ran over the top of Prodex. Inner skins were able to compress the 1/16" edge of Prodex which made a better air tight seal between two separate chambers. In direct sun and temperatures of 102 degree I only run my 15000 BTU low profile Carrier on lowest setting. Thanks, "Boatdoc"
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Old 01-04-2011, 01:59 PM   #17
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This is great info. Any chance you took pictures during your installation?
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Old 01-04-2011, 02:10 PM   #18
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Thanks BoatDoc! I like your idea of leaving a 1/8" gap for moisture drainage and will incorporate your idea. I've said it before and I'll say it again "This forum is GREAT!"
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Old 01-04-2011, 02:42 PM   #19
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One of the things not mentioned here or in other threads I have seen on insulation installation: The last step of installing the Prodex is to seal around all edges to maintain a sealed airspace, yet it is discussed as if the spaces are not being sealed. I would bet the surface of the insulation creates a much better vapor barrier than the aluminum skins did originally, what with all of the rivet holes and unsealed seams. In fact, there's little chance of moisture getting into the wall from the inside now at all.

Rich the Viking
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Old 01-04-2011, 05:35 PM   #20
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Although it is desirable to allow any liquid water to travel from ceiling to floor so we might* have a chance to observe it - the chimney effect of an open cavity airspace in our Prodex installs (from floor to ceiling) will reduce R-value overall.

Cold will drizzle down and warm percolate up allowing faster diffusion whichever way we want to look at it. That is another point that fiberglass has to its merit - true dead airspace within its matting.

I expect to use white 3/4" foam cut to fit for a horizontal baffle every eighteen inches inbetween the two layer method - and the shell layer of Prodex held off from the outer skin by strips of Prodex.

I like the sandwich method of OP for areas needing more sound proofing, helps with both inside-to-out and outside noises in. When a Home Depot closed up here I nabbed two cases of their "Handi" wrap 2-inch thick by 5-foot long rolls for 90% off and plan to use them near the seating and sleeping areas from top of windows down. Also plan to use it around the four speakers cut into the liners for better sound where the patches to remove them would be uglier than the speakers...
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Old 01-04-2011, 06:13 PM   #21
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I spoke with a jonathan from prodex. He did confirm that some air space between layers is most effective for their product. However he did say that the prodex would still be effective directly glued to the aluminum. Also on their website, it says you can combine and layer other products to increase r-value. So just to be safe I will fir out the walls and use 6 layers of prodex, 3 layers of dead air space and a couple layers of fiberglass. That should show the condensation who is boss.
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Old 01-04-2011, 08:30 PM   #22
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Hi Matt

Is your Prodex silver? It was hard to tell in the picture, if it was the same product that I saw online. ( And it appears that they make several products for different applications) Dave
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Old 01-04-2011, 10:13 PM   #23
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The prodex in indeed silver on both sides, with a white foam in the middle, and no, it does not taste like oreo cookies.
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Old 01-05-2011, 11:44 AM   #24
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The ribs are a significant heat leak. Dave Park suggests using a butyl tape between rib and inside skin - is this the usual rather thick stuff often used for appliance flanges on exterior skin?

I wonder if just running Prodex across the rib before attaching the interior skin would be effective as well for rib insulation. That could be run as a continuous layer rather than panels.

How thick is too thick between interior skin and rib?

The glue for block foam spacers is a long term concern, I'd think. I know one should not underestimate the power of modern glue but the decomposition of the block foam in a flexible environment seems to be related to the whole issue of using foam insulation in travel trailers.

Never underestimate the power of condensation! Ventilation is absolutely necessary despite its potential heat loss. Consider the situation in controlling interior condensation during cold weather or the use of catalytic heaters.

I believe Prodex(tm) is a brand name for a specific foil-foam-foil insulation product. You can more easily find foil-bubble-foil insulation at Home Despot or Lowes from what I can tell. I tend to think the foam in the sandwich would be a bit hardier than plastic bubbles.

A previous owner for one I saw seemed to be using dessicated squirrels for insulation. I wonder if the skeletal structure and dead air spaces in the carcass were the insulation factors ... ;-)
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Old 01-05-2011, 12:01 PM   #25
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Personally, i would prefer a thinner butyl tape, as ANY presence reduces heat transfer. The other consideration is that the firmness of the bond of the inner shell to the ribs is a good proportion of the overall strength of the shell, and having an adhesive element involved would be a lot stronger than having non-sticky prodex. IMHO.

I don't think vapor is a problem, and non-dripping condensation isn't a problem for aluminum or prodex or the foam boatdoc specified. That foam tolerates heat, cold, moisture, flexing, glues well, etc.

Automotive adhesives seem up to the task.
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Old 01-05-2011, 12:37 PM   #26
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I've spent a bunch of time thinking about isolating the liners. 18 months ago I glommed onto enough mil-spec dense silicone sheeting to make isolation strips for the 200-plus feet of liner-to-rib contact areas.. BUT:

One can use anything they want for interior liner isolation off the ribs BUT its absolute necessity to reproduce the factory fasteners metal-to-metal clamp action that originally displayed zero movement in all axises - at least until the first 'Dukes of Hazard' style jump over a curb that flexes the shell enough to relax or shear the blind rivets shaft.

Even my dense silicone sheet crushes down somewhat so the interior liners will be dimpled around each rivet and there will still be movement, the trip up the Al-Can Highway would have the liners flying in loose formation before we could make the return trip.

Putting an aluminum stand-off washer the thickness of the silicone sheet at each attachment point gets complicated, and doing that correctly would mean welding each tie-point area to the rib to get back to maximum strength - and probably doubling the number of fasteners for good measure..

Something inert and physically incompressible with a low heat-transfer property - I have yet to find the right material. Something like high temperature gasket paper? Just enough thickness to block the Al to Al contact. How about a couple of coats of chromate paint to give 5 or 8 mill thickness?

IS using Butyl tape and having it double-sided adhesive essentially gluing the liners up and holding it there with blind rivets securing the glue bond really a dependable format FOR VINTAGE TRAILERS? Not what the factory can get away with now, with all clean components and the unit never having been warped from true by 30 years of use, abuse or neglect...
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Old 01-05-2011, 12:58 PM   #27
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Would simply painting the ribs help slow the heat transfer? I once read about a special paint that had tiny beads in it that added significant insulating properties to it. They were using it on the underside of roofs as well as walls for heat and sound properties.
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Old 01-05-2011, 01:45 PM   #28
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One of the things not mentioned here or in other threads I have seen on insulation installation: The last step of installing the Prodex is to seal around all edges to maintain a sealed airspace, yet it is discussed as if the spaces are not being sealed. I would bet the surface of the insulation creates a much better vapor barrier than the aluminum skins did originally, what with all of the rivet holes and unsealed seams. In fact, there's little chance of moisture getting into the wall from the inside now at all.

Rich the Viking
Hi Rich the Viking and SilverHoot;

It seems as this thread will go controversial very soon. Every one seems concerned about minute unattainable details but fail to see the big picture starring them right in the face, their windows. They are concern about small weep holes for drainage of condensation. Yes those tiny nasty little weep holes that can create a chimney effect in your trailer and cause you to freeze to death while you asleep. Lets face it friends, all we are trying to do is insulate a trailer not a space ship.

Please keep in mind that design of the trailer makes it totally impossible to successfully combat everything that Mother Nature will throw at it. We can only attain it to a degree because we are not faced with a single issue. It is the constantly varying temperatures, humidity and thermal transfer. You have to give up something to make something else work, such as drainage from enclosed by Prodex air chambers. I will explain later why chimney effect cannot take place in a properly insulated trailer.
It is just not practical to spend thousands of dollars to insulate the walls to NASA specifications when we sustain a great loss through glass windows. It is foolish to spend thousands of dollars and enormous effort to save 5 lbs of LP fuel in a year, when there is only so much effectiveness to be had.

Prodex and other forms of foil type insulation are most effective ways to insulate, providing it is done properly. It also offers best moisture barrier, it is resistant to deterioration due to vibrations. On the opposite side a fiberglass insulation does not offer a true dead air space as some claim. If the moisture barrier is compromised it no longer serves as dead air space. Paper moisture barrier also deteriorates quickly under extreme heat conditions.

My 1973 Argosy was insulated with bubble foil and in 102 degree direct sun I run my 15000 BTU low profile Carrier, only at the lowest setting.
Here is step by step how it was done.

We purchased 4' X 8' X 5/8' thick urethane sheets which were cut easily with utility knife to 1.5" wide strips. Each open section between the ribs was measured. Strips were cut to proper length and the two verticals were glued in first, next to the vertical ribs. The two horizontal strips were cut 1/8" short. This is to provide minute drainage from each side in each section. Center vertical strip was cut 1/16" longer so that it would seal each section from the other. As the end result you will have a rectangular frame with vertical divider sealing the two air chambers in the middle. With only one weep hole per chamber no chimney effect can take place, however it will release pressure as air expands in extreme heat.

Glue; I have chosen to use a spray glue made by North Star Chemical Inc, called Star Stuk. While it is rather on a expensive side, it goes a very long way because you can use it very sparingly. I would lay pre-cut strips on a piece of cardboard close to each other to minimize over spray loss. Couple of minutes after applying the glue I would place them in the corresponding place. Next I would pre-cut Prodex 2" larger than the opening on every side. This excess will allow you to glue the insulation along the sides of the ribs. Mark a vertical center on the horizontal ribs to serve as guide when gluing in Prodex. Do the same on Prodex panels. Next, spray tops of the glued in strips and sides of the ribs. Align your vertical marks on the frame and the panel and be sure to adjust the panel to proper height and stick the panel to the center vertical strip first. Tuck in the foil in that area to top and bottom rib. Using both hands one on top the other on the bottom stretch the panel up on the top and down on the bottom working your way to wards the side then do the opposite side. Tuck the excess 2" of panel to the side of the rib. Double check all glued areas to ensure adhesion. Next day trim the excess Prodex to about 1/16" above the surface of the rib. That will compress and create a better seal on the inside skin. Working with Prodex is a breeze because it is easy to handle and form. Some sections may be harder to seal than others, and you will have some openings here and there. There is no way to thermally seal an Airstream unless you have NASA do the work. Do not forget to replace all your windows with Solar Guard thermal panes as well or else your effort in details will be futile. Thanks, "Boatdoc".
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