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Old 03-04-2016, 02:21 PM   #1
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Ceiling other than wood or metal

After seeing the wood plank mounting post, I searched the forum for alternative ceiling materials. I'm still not really satisfied with what I found and will explain how it all sits in my head right now.

Insulation plan:
I plan on using foam-it green in both the open spaces between the ribs, as well as filling the ribs. This insulation will be applied after all avenues of ingress are properly channeled, such as wiring holes and vents. Windows will already be installed so I don't have to cut through the insulation. The ribs will be either pre-covered in a thermal barrier material, or strips added after the foam. The foam will be trimmed flush with the ribs.

Visual appearance:
I want to at least simulate the look of the ribs by adding a strip of material on top of whatever I use for the ceiling. I'm sure I can find either a stick-on material or something similar. It will be either metallic looking or just painted. I am trying to achieve an industrial or WW2 era vehicle look. I also want to have the thinnest material possible since I am tall and every 1/4" counts.

Material Problems:

Metal will still be an avenue for condensation, and would add back a lot of the weight I'm trying to save. It would have to be attached by a lot of fasteners which I don't really mind. Metal would be the thickness I like, and painted, would be the finish I'm looking for.

Wood I see as a material that would absorb moisture and be prone to mold, but would be closer to the weight I'm looking for and might be able to provide the finish I want after many coats. Very thin sheets are available that would not subtract much interior height.

Plastic panels could give the finish I want, acceptable weight, allow me to see the original marked holes in the ribs to mount if transparent, and be paintable resulting in a very smooth finish. My concern here is that the minor flexing of the body may cause the panels to crack where they are screwed into place. I could possibly make a system using a LOT of 3M tape, which I have, that would bypass the need to screw the panels into place.

Thin rubber sheeting, similar to what was pulled off the floor might be too heavy, would pull through any regular screws, would look too strange with huge washers, would be a lot heavier than carpet and would require much more flat surface area to mount with industrial tape. It would look pretty cool though, would not be that paintable and would definitely put a certain "flavor" in the air that would probably not be ideal.

Materials summary:
Acoustic tiles and plywood: too thick

Carpet and any fabric type material: neat idea but would need a solid base to mount to, so I might as well use that solid base as the ceiling

Any wood material: too moisture absorbant

Any metal material: condensation haven and heavy weight requiring many screws to mount, creating too much thermal bridging

Plastic: concerns with cracking due to temperature and body flex

Rubber: stink, weight, mounting issues more demanding than carpet


Please correct me where I am mistaken, since I'm not overly familiar with any of these materials other than normal human daily experience. For example, if there is a coating that I could put on wood panels that would seal them indefinitely and not degrade the wood to where it would delaminate, then let me know. If there is a thin plastic material that would be resistant to cracking, let me know.

Right now, I'm leaning towards plastic panels stuck to the metal structural elements using industrial tape. The attachment points will be at the ribs and intermediate beams I will add. Using foam tape would remove the need for metal hardware to attach the panels, thus removing an avenue for thermal bridging. The VHB tape I would use would also allow for a minor degree of flex when cured, hopefully allowing the panels not to stress to the entent that they would crack. Gaps between the sheets would then be taped over with a similar tape, and the simulated rib attached.
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Old 03-04-2016, 02:54 PM   #2
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You could use that cedar closet planking or something similar for the ceilings to avoid rot issues. It's thin and light and a fairly good insulator.
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Old 03-04-2016, 04:12 PM   #3
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How about using fiberglass panels? They come in 4'x8', should resist cracking and are easy to wipe down.
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Old 03-04-2016, 04:23 PM   #4
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Quote:
Originally Posted by dgorila1 View Post
How about using fiberglass panels? They come in 4'x8', should resist cracking and are easy to wipe down.
if you have a semi trailer manufacturer in your area[ we have utility] they will sell the left over pieces from rolls by the pound.i got a trailer full for 40 bucks.
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Old 03-04-2016, 04:51 PM   #5
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After insulating the ceiling of my ToyBox I screwed FRP panels from Home Depot to the ribs. Smooth side out. I think that I've seen a little bit of seasonal expansion/buckling but only in corners. Nothing is damaged. Predrilling over-sized holes might eliminate buckling...that's for the next build. Tape would be a good option I think.

I doubt that a wood paneling would be a moisture sponge with reasonable ventilation. If you're worried, add a vapor barrier underneath then paint the wood, all six sides. Wood seems like it would be the heaviest option.

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Old 03-04-2016, 06:21 PM   #6
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I'll second FRP as an excellent choice. It's flexible enough to bend at the root of the roof radius, and rigid enough that it doesn't flop. I used a different material from FRP (because price) which has a bit more thermal expansion but also cheaper, and easier to work with and clean. It also bends more.

I get a little bit of the pillow effect which bothers me in some respects, but I'm completely at peace with actually. If it gets bad I could just do frp instead.

So basically, I have: bus external steel, followed by rigid board insulation, then the internal plastic. I use FRP rivets to hold things in place into the strapping panels.

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Old 03-04-2016, 08:19 PM   #7
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I'm not sure I follow the concern for condensation on a metal surface on the interior side of the insulation you described. Condensation happens when a surface temperature is below the dew point. Why would metal interior facing be so much colder than the room air? Usually one of the objectives of insulation is that it should slow heat loss enough that the interior surface of the insulation is warmer than the dew point. By extension, the facing over the insulation would be that warm also and no condensation should happen. What am I missing?
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Old 03-05-2016, 05:46 AM   #8
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family wagon: My thinking on the inside metal is that it would be cooled much faster than the surrounding air due to conduction from the exterior passing through all of the screws. In the summer, the metal ceiling would be like a mild heating element, and in the winter, a mild freezing element. The ribs would for sure with no real way to prevent it, so anything attached to the ribs would be an extension of that effect. I could be wrong, or possibly overestimating the effect, but it seems to logically follow. I've seen videos of thermal bridging in homes through the 2x4 framing and am just imagining how much more of an issue it would be with metal.

The FRP looks pretty interesting and I will check that out.

aaronsb: Are the strapping panels the metal strips I see between the white ceiling panels? If so, do the plastic panels then slip under them similar to a dropped ceiling? I really like the look.

I do plan on active ventilation and will not be using any propane systems at all in an effort to keep excess humidity to minimum. The bathroom area will be as completely sealed off from the rest of the bus as I can make it.
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Old 03-05-2016, 12:31 PM   #9
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Originally Posted by RHOMBUS View Post
The ribs will be either pre-covered in a thermal barrier material, or strips added after the foam. The foam will be trimmed flush with the ribs.
Ahh, maybe I misunderstood this part. I was thinking the pre-covering with thermal barrier is on the face of the rib where the ceiling/wall finish mounts. But maybe it isn't..? I guess I was thinking that with some insulating layer between the ribs and the interior finish, even though it's thinner than the rest of the insulation, maybe the thermal bridging wouldn't be too bad. A metal panel could be adhered with VHB mounting tape too. I don't know offhand what's the weight difference between say 24 ga steel and 1/8" FRP or HDPE plastic.. per The Engineering Toolbox, that steel weighs 1 pound per square foot.
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Old 03-05-2016, 03:22 PM   #10
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Yeah, I kinda ran a lot of ideas all together at once in my first post. One option is to pre-cover the ribs, but then as I think about that, how would I attach anything to the ribs if I can't see the original holes? I'd rather not drill any more holes than are already there, but I don't really see any other way around it. In that case, the metal screws would still bridge, although not nearly as much as a bare ribs would, so you read it correctly. However, the more I thought about all of the x hundred screws, the more I thought it wasn't such a good idea. The VHB tape won't be secure on just the rib covering, so that would have to be passed up, and thick VHB would provide some kind of minimal thermal break. Maybe I should just quit trying to over engineer things. I'm still going to want to attack studs to the ribs in the ceiling and walls, thus creating the same situation. Perhaps the thermal material will eliminate enough to not stess so much over the rest of it.

I have been accused on more than one occasion of overthinking things. This is probably a good example of that.
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