Sandwich Side - Ceder framing

[fseider]

I'm trying to keep the weight down as much as possible - Is this a good idea for a 4 X 8 TD?

Ceder framing
3/4 insulation (Must have some insulation at a minumum)
1/8 ply inside and outside.

Or am I pushing the strength boundaries?

Thanks,
Fred

[Esteban]

Fred,

Guess you're building a portable Cedar Tear Drop Hope Chest? Should smell nice and keep the moths away.

Others will need to chime in about using 1/8" plywood on the outside. Would be a little concerned about the strength and puncture resistance of 1/8" ply outside skins. I'm using fiberglassed 1/4" outside over a 3/4" wood frame and it's plenty rigid.

Part of my sandwich frame is made from salvaged old growth redwood. It splits too easily when I used pocket screws so I didn't use as much of it as I anticipated. Cedar is pretty rot resistant too, isn't it, so go for it. On the hinge side of you doors and hatch use a wood that will hold screws well. That's where I'm using popular. Most of the rest of the wood frame is made from Orange Box pine boards and cut up 2x4's.

[Juneaudave]

Fred...I agree with Steve with the 1/4 on the outside and using hardwood on the hinge points. Just be sure that if you are ripping some 4/4 ceder that you can find insulation to fit...it's not true 3/4 inch...and in my location...I could only find 1" insulation.

[tinksdad]

I'm not giving advice here because I am far from an expert. Just relaying some info from personal experience. I used 1x3 cedar from the box store for my floor framing. I wanted a little extra stock on the ends of the floor because I was going to have to trim them to match the profile curve and didn't know the exact angle. I made the floor a little lon on both ends, put the wall in place temporarily, marked the curve where the two met, removed the wall and trimmed the floor to that angle. It worked; but in retrospect I wouldn't do it again. Cedar, like all woods, comes in a variety of grades.

Like Dave said, The stuff from the box store wasn't a true 3/4". If I had to do it over, I would have used poplar like I did for all my spars.

Not the greatest pic; but it shows the angle where the floor had to match the wall profile and a couple of the poplar spars I added later in the build..

[asianflava]

I've got 1/8in inside and out. Been fine for the last couple years. I put 2 layers on the roof but I don't think I needed it. My tear is covered with aluminum so that gives it pretty good protection from UV and water. I also put 2 coats of epoxy on the wood before I covered it with aluminum.

Mine is a 5X10 so there was weight to be saved. All up ready to go weight (minus food and clothes) is 1100lbs. That includes the airconditioner, mattress, and battery. I've heard from a couple of people that sandwich walls on a 4X8 doesn't really save all that much weight.

[fseider]

Seems like I should probably go with something else, like poplar, which was my first choice anyway. I'm just trying to determine where I can save a few pounds here and there, as it does add up. The strength of the door support frame is something I did overlook - oops! First build, can't you tell.

As to the 1/8 vs 1/4 - I've receiver mixed responses previously on this - some say 1/8 is more than adequate, others say 1/4 is a minimum. I'd like this to be a solid structure, but not a tank like enclosure. (I do have some plate steel around, but that may be a tad bit extreme. ) I'll double check the weights and overall it could be OK with 1/4.

As for dimensioning - not a problem - I have a full shop here - tablesaw, joiner, planer, etc. The only thing I don't have is adequate space. Hmmm, maybe if I gave some of the tools away I'd have the space .....

Thanks,
Fred

[Arne]

I went with luan outside and inside. more than 1/8, less than 1/4... 1/8 inside should be fine. glue it to the insulation to keep bowing/puckering down.

Every pound counts. I over framed my walls and floor, due to slack on the design, not knowing exactly where things needed heavier timber for reinforcement.

But, the reality is the most I could have saved would have been about 50#.. wound up at 1,100 ready to go.

If you are going with 1/8 on the roof, do not leave a flat spot for the vent, if you have a vent in mind...... a continuous curve is much stronger. I put in the flat spot and now wished I had made the curve continuous and fit the vent to the curve with fillets..... I would have liked the shaped better, also.

see page 13 in link, about 1/2 way down.

[Esteban]

My teardrop will be 5'3" wide by 10' long on the floor with about 11' long walls. So I'm trying to save weight where I can. I bought Steve Fredericks CD and am building using his "inside out method." Walls are sandwich construction with 1/4" ply outside, 3/4" framing and insulation, and 1/8" birch ply inside.

I ripped 2x4s into 3/4 x 1-1/2" boards to use as roof spars. They'll span 62-1/2" from side to side. Have glued some together to end up with 1-1/2 x 1-1/2" spars with alternating grain thinking they'll be stronger than one piece ripped to the same dimension from a 2x4. Will use the beefier spars where 1/8" plywood roofing sheets meet to have more to glue and staple into. Plan to skin roof with two layers of 1/8" plywood.

Will install all spars with the crowned side up. Also cut out blocking shaped like the roof curve to use mid span between each spar, so adjacent spars work together to carry the roof load, so the roof doesn't sag.

Used ripped 2x4s for some wall framing (saves $ and I can control dimensions). In other areas I used nominal 1by boards cut to follow the side wall to roof profile and biscuit joined and glued together. Used popular on hinge side of door opening. Popular is heavier and more $ than pine boards or (doug fir?) 2x4s so I only used it where its extra strength was useful.

Like I wrote in an above post I used some salvaged heart redwood I had on hand for wall framing. But not as much as I anticipated because it split too easily when two boards were joined with pocket screws.

My walls seem pretty light weight and strong so far.

Still need to insulate them, install wiring chases, and glue on the inside 1/8" birch before attaching them to the floor. The outside ply was fiberglassed working flat on a work bench.

[Ivar the Red]

I have a question...do you nail the thin stuff to the frame work? Or just glue? Do you use something like Gorilla Glue? If nailed, you don't use very big nails, do you?

Hmmm, that was 4 questions, very interested.

[Arne]

I used a brad nailer with #18's... very small, but good enough till the glue dries.

[del]

I have a question...do you nail the thin stuff to the frame work? Or just glue? Do you use something like Gorilla Glue? If nailed, you don't use very big nails, do you?

Hmmm, that was 4 questions, very interested.

Air staples and Titebond II.

del

[Esteban]

I have a question...do you nail the thin stuff to the frame work? Or just glue? Do you use something like Gorilla Glue? If nailed, you don't use very big nails, do you?

Johnny, I used a pneumatic stapler, and tite bond II glue, to attach 1/4" plywood sides to the 3/4" wood frame. Fast. Fun. Holds well.

Since then I bought a pneumatic brad gun too. Probably either tool and type of fastener would work fine. Will use the brad gun more for finish work or where staples would be too short. Will mostly use staples where they won't show. I've read about pin nailers that drive pins that are so small they don't show up in finish work...would be a nice tool for a woodie or for finish cabinet work.

For the roof probably will glue and staple the first 1/8" layer of plywood to the roof spars. Quick. Secure. No need to fill staple divots on first layer. Plan to only use glue to fasten the top layer of 1/8" plywood over the first one. Will use clamps and straps while the glue sets up. Should provide a good smooth base for fiberglassing.

[asianflava]

I have a question...do you nail the thin stuff to the frame work? Or just glue? Do you use something like Gorilla Glue? If nailed, you don't use very big nails, do you?

Hmmm, that was 4 questions, very interested.

All I used was epoxy and epoxy thickened with microfibers. Apply epoxy to the face with a roller, then put thickened epoxy on the frames. I put one or two screws into the face to keep it from moving when I put the weights on it. I took the screws out once the epoxy cured up.

[Ivar the Red]

What if I'm air tool poor?

[satch]

What if I'm air tool poor?

If you're gonna paint or skin with something else, you can use screws, and when the glue cures, remove them and fill the holes with bondo/putty.