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Old 03-09-2015, 07:53 PM   #1
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How to reduce thermal exchange sweating on ceiling

Been trying to figure out where water was coming from at the bottom of the inside walls on my Bluebird All American. Finally figured out it's from the ceiling of the outside metal skin of the bus roof.

Without skinning down to metal and starting over are there other viable thermal options??

Thanks!!....Mark

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Old 03-10-2015, 10:36 PM   #2
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PS...I'm talking about thermal sweating - condensation from extreme temperature changes causing excess water to pool and run off the outer skin of the ceiling (can't see it till it runs out of the bottom of the wall panels). Any ideas how to stop it??
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Old 03-11-2015, 12:11 AM   #3
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Are you sure you don't have a leak? My suggestion (leak or not) is to coat the roof with an elastomeric roof coating.
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Old 03-11-2015, 12:27 AM   #4
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Positive - No roof leak

Thanks for the thought, but I am positive it is not a roof leak. My roof is solid, no degradation. I took a couple of lights out of the ceiling, moved some insulation out of the way, and sure enough the inside of the metal roof was sweating like crazy.

Would an elastomeric coating on the outside actually help contain that? I reeeeeally don't want to rip out all the rivets on the inner ceiling to fix this problem.

Thanks!...Mark

PS...I should mention there was about 2" of ice on the roof at the time, and I was running a propane heater inside while working on the floor.
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Old 03-11-2015, 02:11 AM   #5
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The propane heater will add a LOT of water to your environment if not a vented one. The only way I know to reduce or eliminate condensation is to either have surrounding materials that will absorb and release slowly the humidity (I had a utility trailer with steel roof and masonite side panels that never condensed. The other way is to eliminate the metal to air interface with spray foam or some sort of coating that won't allow the thermal transfer to allow the water to condense when the dew point is optimal for such. Think tight fitting koozie on your beer can.
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Old 03-11-2015, 09:45 AM   #6
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The elastomeric will help a little as a thermal break, or rather it did in my situation. It helps a lot with the NM heat transfer. Get a dehumidifier and dry the place out as fast as possible. TN has high enough humidity that cracking a window while running the LP heater isn't going to help a great deal. I use LP but no humidifier. Before I head back east, I will be installing one with an exterior drain. I just need to find a place to put it.
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Old 03-11-2015, 11:45 AM   #7
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Thanks for your time and thoughts! My objective is to get comfortable and functional without spending a pile of cash....as I have other things to spend the pile upon...LOL! I think I will try the ceramic insulated elastomeric roof coating, then maybe try to invent some type of roof venting airflow system to accelerate drying in that 2" space area between to two ceiling and roof plates. I do appreciate your input. I had not considered Propane causing excess H2O via condensation, but now that it's mentioned I see it clearly. Thanks again!!
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Old 04-10-2015, 06:11 PM   #8
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venting

My 1980 blue bird had the same problem you need to install multiple roof vents I put 4 in the outer skin and 2 all the way through rv vents work for the through ones. The 4 outer skin ones can be found at any home reno store and are about the size of a hockey puck ... yes im canadian
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Old 04-10-2015, 06:19 PM   #9
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Thanks for the vent info!

Greetings!....Thanks for the vent information. I'll check on the external ones you mention but have a question about the other. What are "through vents"? Can you give me an example of where to look?

All the best...Mark
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Old 04-11-2015, 01:50 AM   #10
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The through vents are just your regular rv vents that you can get at walmart/Canadian tire or your equivalent store .
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Old 04-11-2015, 04:21 AM   #11
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wow, busdan. first two posts are 100% helpful! welcome aboard!
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Old 04-11-2015, 08:39 AM   #12
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Quote:
Originally Posted by Mark Antony Wray View Post
I think I will try the ceramic insulated elastomeric roof coating...
My experience with the insulating beads: http://www.skoolie.net/forums/f13/in...ease-9291.html

In my opinion: not worth it. Not only do they not work as advertised, they also leave you with a crusty paint job.

White paint, on the other hand, is very effective.
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Old 04-11-2015, 11:50 AM   #13
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And I'll add my opinion again about painting the exterior: Use 3M bubbles added to your exterior paint of choice Fillers. I think it's the most effective way (cheap, light) to add insulation on the outside of a bus. Having a crusty paint job is an issue of application.

In the tests that jazty did (which I think are valid) the sawdust helped as did the hytech bubbles. Notice that both of those have insulating properties. There's many websites where you can look up insulating properties of different materials and it shows that wood has good thermal properties, especially when thermal mass is considered. The 3M bubbles also have good insulating properties. They're the same as the Hytech stuff and MUCH cheaper.

Snow is also a good insulator. That combined with the heater is what caused the extreme condensation.
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Old 04-11-2015, 12:26 PM   #14
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OR you could put on a couple more coats of elastomeric paint and have a nice looking, durable roof without
any grit. 2 coats + beads is the same as 4 plain coats, but 4 plain coats looks way better, seals better, and is more durable.
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Old 04-11-2015, 12:51 PM   #15
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OR you could put on a couple more coats of elastomeric paint and have a nice looking, durable roof without
any grit. 2 coats + beads is the same as 4 plain coats, but 4 plain coats looks way better, seals better, and is more durable.
That sounds good. I've never used the elastomeric for my bus so I don't have any experience there.
The bubbles are commonly used as a light weight filler in airplane fiberglass applications so if a shiny smooth roof was high on your list and you don't mind sanding you could go that route. Use a paint that has good flexibility. The most important thing is the color- white is the way to go. Lots of good info on paint temperatures, etc. on HomeBuiltAirplanes.com or any of the other composite airplane forums. Paint color on composite airplanes can be a life or death decision.
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Old 04-11-2015, 03:38 PM   #16
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To anyone installing roof vents.

Don't drive your bus in the rain. You will get more water in the bus than the condensation ever did.

Ventilating hot air is a good thing, however it dose nothing to block the radiant heat. You will still slowly cook like your in a oven.

Insulating the roof in the most important part of any building. The bus roof is even more important due to the fact you have no room to leave enough air space for passive cooling. The fact that it is a heavy gauge metal structure just compounds the problem.

Remove the metal skin on the ceiling and get minimum 2 inches of Styrofoam up there. Plain and simple.

I'm glad others have tested that fake thermal paint and proved it to be a waste of money. Like others have mentioned, white is the best color for your bus roof.

Nat
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Old 04-11-2015, 04:19 PM   #17
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???!! $6.45 plus reasonable shipping charge added to a couple gallons of white paint to reduce the roof temperature an additional 3 degrees (according to jazty's experiment) is a waste of money?

Now if you're talking about the Hytech stuff, yeah it's a ripoff because all it is is the same 3M microspheres.

I agree- 2" foam against the metal on the interior is the best way to go but apparently the OP doesn't want to skin down to the metal.
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Old 04-11-2015, 04:27 PM   #18
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???!! $6.45 plus reasonable shipping charge added to a couple gallons of white paint to reduce the roof temperature an additional 3 degrees (according to jazty's experiment) is a waste of money?

Now if you're talking about the Hytech stuff, yeah it's a ripoff because all it is is the same 3M microspheres.

I agree- 2" foam against the metal on the interior is the best way to go but apparently the OP doesn't want to skin down to the metal.
I was talking about the marked up Hytech stuff.

Nat
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Old 04-11-2015, 05:08 PM   #19
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Cool. Hey, I've enjoyed your build progress - still waiting to see how you're gonna do your windshield...
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Old 04-12-2015, 08:03 AM   #20
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Quote:
Originally Posted by boojiewoojie View Post
The bubbles are commonly used as a light weight filler in airplane fiberglass applications so if a shiny smooth roof was high on your list and you don't mind sanding you could go that route. Use a paint that has good flexibility. The most important thing is the color- white is the way to go. Lots of good info on paint temperatures, etc. on HomeBuiltAirplanes.com or any of the other composite airplane forums. Paint color on composite airplanes can be a life or death decision.
I totally agree on color - I think I've posted the same chart myself. But back on the "bubbles", we called this "micro" (short for microballoons which is what they're usually called when sold, if you want to search for them). Micro was used as a lightening filler. Epoxy is relatively heavy, and there's that rule: if you throw something in the air and it comes back down, don't put it on your plane. When you go to finish the outside surface for paint-prep, making a micro slurry would give you a much lighter material to paint on.

That was its only purpose - it was never used to provide any kind of insulating effect. I have no doubt that micro itself DOES insulate, both because of what it is and because of personal experience. Once in a pot of epoxy, it drastically reduces the working time of that epoxy before it "goes" off - and epoxy full of micro can do this spectacularly. It'll start smoking, turn a nasty brown color, burn holes in things, etc. Epoxy cures through a chemical reaction that gives off heat, and heat also makes it go faster. With micro in the mix, this happens a lot faster. You can literally go from 45 minutes down to 5-10.

At the same time, all insulators are measured in terms of thermal resistance per unit of thickness. Micro isn't magic, and in the millimeter of thickness you'd have in a few coats of paint I seriously doubt you'd get any kind of significant R-value increase. I know a lot of people put stock in these things, but if anybody ever actually did a serious, scientific evaluation of them I would bet heavily that most or nearly all of the effect came from the color and reflectivity of the paint, not the balloons themselves actually preventing conductive heat transfer.
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