wall construction

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wall construction

Postby Irishexplorer » Sun Sep 13, 2020 7:10 am

hello to all, I am a first time builder looking for advice on what to us for the walls of my teardrop. personally i was considering 6mm ply, 2x1 frame with 18mm insulation and 6mm ply again. what are your thoughts?
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Re: wall construction

Postby noseoil » Sun Sep 13, 2020 7:41 am

A lot of people have had good luck with a "skeletonized" plywood frame wall (myself included). I used 3mm Baltic Birch plywood for the inner & outer skins, 3/4" plywood for the core, with insulation to fill the voids. It has been a strong, light & pretty robust panel for the sides & has held up well to traveling both on & off the roads. It's a good system and much easier than having to glue & join all of those small pieces together. Not right or wrong, just what I did...

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Re: wall construction

Postby saywhatthat » Sun Sep 13, 2020 7:54 am

big fan of fiberglass skeleton frame. can work on it 10 to 15 minutes at a time no warping ,easy to fix oh-ho. Never worried if it gets damaged no rot. So easy a caveman could do it. I can glue a join better than cut a strati line in wood
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Last edited by saywhatthat on Sun Sep 13, 2020 12:55 pm, edited 1 time in total.
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Re: wall construction

Postby tony.latham » Sun Sep 13, 2020 8:44 am

This is why I build using sandwiched wall construction.

Let me start out by defining this type of construction. A sandwiched wall includes an internal structure –I use heavily skeletonized 3/4" plywood– that is sheathed on both sides with thin plywood. For the interior sheathing, I use 1/8" Baltic birch. On the exterior, I sheath with 1/4" plywood. The voids in the internal structure are filled with foam board.

1. The resulting structure is a torsion box that is stiffer than a single sheet of plywood with close to the same weight.

2. This method makes it easy to "stretch" plywood beyond the normal 8' length using a simple spline joint in the skeleton cut with a router bit. The exterior/interior sheathing that is glued on acts as a gusset and strengthens the joint.

3. Insulation. I purchased my first teardrop in 2004. It had solid plywood walls. On cold mornings we would always get condensation on the walls. We kept a bath towel in the cabin just to wipe them down in the morning. This would happen even with the cabin well ventilated. Condensation doesn't form on insulated walls.

4. A thicker wall allows for deep dados (or slots) to be included in the wall for bulkheads and any other cross members. This joinery makes for a much stronger cabin and is easier to assemble since these parts just slip inside the walls. Think mortise and tenon. (And yes, this is easy to do with a simple router jig.)

5. The thicker wall allows for a lip to be formed on top of the wall so that the headliner can be installed prior to the spars. This creates a perfect interior wall/ceiling joint that doesn't need to be covered by trim. (Having done this a few times, I can't even imagine having install the headliner after the spars are installed.)

6. The thicker wall allows for a Fredricks style hatch that has a seal system that is water and dust proof.

Sandwiched walls are more labor intensive but you end up with a stronger cabin that is insulated with a galley that doesn't leak.

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Good luck with your build! :thumbsup:

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Re: wall construction

Postby linuxmanxxx » Sun Sep 13, 2020 11:52 am

If you go the stick framing and 1x2 make sure they are good and straight. Glue and an air nailer make this the fastest and lightest build method and a complete glue up gives incredible strength to the weight you save. Once assembled it gains even more strength. The roof has to be doubled in thickness and the framing sticks done vertical instead of horizontal like all the other walls and floor. You need the extra rigid it gives so the roof won't sag. I did a simple 4x8 around 42"interior height with manufactured door and was right under 500 pounds with a steel trailer.
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Re: wall construction

Postby Irishexplorer » Sun Sep 13, 2020 1:20 pm

That's a great help thanks a million. Just one question, why does the roof need to be double the thickness of the wall? I'm planning 8ftx4ftx4ft high to suit sheet material. the only insulation in 18mm is polystyrene, would that be suitable?
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Re: wall construction

Postby linuxmanxxx » Sun Sep 13, 2020 3:40 pm

If you leave it the same width as the walls, due to the size you have to span it will sag in the center. Turn the boards up and down and double the foam and glue it all will prevent the sagging. I did square box with a curved front radius at the top for wind and looks. If you do any curves like the traditional teardrop gives strength to the roof as well but still needs to be stiffer than the walls.

I attached the walls and everything using glue and long drywall screws and could stand 200 pounds on the roof. The glued surfaces of the Luan and foam give crazy sheer strengths with just 3/4"foam walls and floor. I used 3M water based contact cement which is a little pricy but easy to apply and not toxic at all and the green one darkens so you know when it's ready to stick together. Since it's glue it also adds a lot of waterproofing attributes.

I did Luan on outside and paneling on inside then glued aluminum over Luan. Glued everything with the same 3M glue which was developed 60 yrs ago to glue formica to countertops. Doesn't stink and quite easy to work with.ImageImage

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Re: wall construction

Postby saltydawg » Sun Sep 13, 2020 4:02 pm

I will be probably yelled at and put down. After years of reading here and other places I think using wood for anything other than cabinets is kind of foolish with the other options out. Yes the other options are slightly more expensive and take a greater skill set, but they dont rot. And if I did wood, I would fiberglass the exterior 100%, at a minimum PMF.

I see pics and stories of rot, and its never just a little rot, by the time its found its bad.

Doing a laminated panel with fiberglass or aluminum panels is I think actually easier than wood. Its as simple as make a big panel, then cut to shape and glue it together. Its an inside skin, foam and an outside skin with epoxy holding it together. But no wood. It does take a little more planning, but there are plenty of resources out there to figure it out.

Then you only need to worry about rust on the frame.

Oh and welcome to the forum.
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Re: wall construction

Postby saywhatthat » Sun Sep 13, 2020 6:03 pm

foam and an outside skin with epoxy holding it together.
I have thought a bit about a foam glass trailer pod . I would bet if you used the right foam you'd not need any epoxy. I think I seen it some ware ;)
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Re: wall construction

Postby noseoil » Mon Sep 14, 2020 7:49 am

For the roof spars, use 19mm X 57mm (or whatever double the insulation you have available works out to19mm, 25mm, etc). The spars need to be put in edge-wise, so there isn't sagging in the roof, as was said. Any slight crown should be placed up, so there isn't any ponding on the roof. That's what was done on our build & it's plenty strong, stiff & has held up very well (5' wide). I cut the first layer of foam in place, made grooves for wiring, then skinned a second layer in place to cover things up.

For curved sections, just cut a slit in one side of the foam (a kerf) & it will bend into shape for you. The space between kerfs is determined by how tight you need to score for the radius of the curve to bend smoothly. Watch out for the glue, some solvent-based glues will eat foam. Cheap latex caulk will set up well & bind the layers together into a solid block.

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