Why use plywood?

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Re: Why use plywood?

Postby slowcowboy » Mon Feb 27, 2017 9:35 am

Number one I didn't leArn welding so I can produce nice work with wood..i am like a duck in chickens with metal..

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Re: Why use plywood?

Postby Gator417 » Wed Mar 01, 2017 2:42 am

I think some people are confused at my question. Plywood is the heaviest material one could possibly use in a camper. I'm asking why use it if it is so heavy and prone to rotting and delaminating. In response I get "think plane, not tank". I've built RC airplanes. before. I used either foam or balsa framing with plastic covering. I did use minute amounts of plywood, but they would have never flown if I built them primarily out of plywood.

KennethW wrote:Sorry I did not do a build thread. At the time I did not Know it would work.
(Foam cooler glued to a trailer covered with canvas going down the freeway at 80 mph. WHAT could go wrong?)

That's too bad. Hopefully there is something in your pics I can use, otherwise I'll be bugging you all the time with silly questions. I'm also going for a budget build & not going to use any wood if possible, so I'm looking hard for ideas I can use right now.
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Re: Why use plywood?

Postby aggie79 » Wed Mar 01, 2017 9:01 am

Your goal for no wood is laudable. That said, I'm curious as to what type of structure/structural material you'll use to anchor/attach your door(s), hatch, roof vent and other "appendages" to your woodless build.
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Re: Why use plywood?

Postby rruff » Wed Mar 01, 2017 10:49 am

aggie79 wrote:Your goal for no wood is laudable. That said, I'm curious as to what type of structure/structural material you'll use to anchor/attach your door(s), hatch, roof vent and other "appendages" to your woodless build.


You can buy fiberglass square tubing, which is a little pricey but not bad if you don't use a ton of it. Laying up fiberglass by hand will also work.
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Re: Why use plywood?

Postby rruff » Wed Mar 01, 2017 10:56 am

Gator417 wrote:That's too bad. Hopefully there is something in your pics I can use, otherwise I'll be bugging you all the time with silly questions. I'm also going for a budget build & not going to use any wood if possible, so I'm looking hard for ideas I can use right now.


You should be in the "Foamies" section. Plenty of info there for you. viewforum.php?f=55

BTW plywood is very efficient (strength and weight) if it's used in thin sheets as a stressed skin. The problem is penetrations and eventual rot.
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Re: Why use plywood?

Postby tony.latham » Wed Mar 01, 2017 11:24 am

why use it if it is so heavy and prone to rotting and delaminating.
:thinking:

Huh? A camper made from a high-grade exterior plywood will last many generations if the wood is sealed from moisture (preferably with epoxy) and protected from UV rays.

And it doesn't have to be heavy.

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Plywood. :thumbsup: :applause: :thumbsup:

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Re: Why use plywood?

Postby JaggedEdges » Wed Mar 01, 2017 12:10 pm

Gator417 wrote:I think some people are confused at my question. Plywood is the heaviest material one could possibly use in a camper. I'm asking why use it if it is so heavy and prone to rotting and delaminating.


Okay... 1/16 sheet steel 8x4 80lb, 1" 1/16 plywood 8x4 80lb, that's some pretty thick plywood to weigh the same as some not very thick steel.

Also if you're thinking "lightweight steel studs" ... they're only lightweight if they're for indoor non-structural framing, basically to gap drywall off something solid. Structural steel studs basically same weight as a 2x4.

It's prone to rot and delamination if you don't protect it, but everything else also has issues is you don't use it right. Plastics have UV problems, steel can have rust issues, and terrible condensation issues, brings the cold right in, as would aluminum structure... gets complicated to insulate. You are aware that's there's 50+ year old vintage Plywood Cruisers around that have been on actual water their whole lives, protecting it can be done effectively.

I've seen plywood used extensively on RC aircraft, it was dependent on special 1/32 and 1/64 hobbyist plywood though. 1/32 for the fuselage, 1/64 for the wing skin. Piece of common or garden 1/8 for the firewall. Was more popular in Eastern Europe during the time they couldn't get any balsa though. They'd be making wing ribs out of orange crates and cutting holes in them to lose a bit more weight.

Sure there's tonnes of things you could theoretically make it from, but lacking things like an inert atmosphere for welding, a curing oven for high tech composites, etc etc, plywood is the one that works in teh average garage.

Let me tell you about modern composites, they have most of the resin sucked out of them by vacuum, then are oven cured. if you don't have the means to do that, you end up with heavyweight sh** that was just nasty and smelly to make. Rutan makes some foam core fullsize planes, but it ain't a particularly popular homebuild aircraft method.

Now foamie and PMF looks promising, but there's still issues to solve for scaling it up much, hard points can be an issue, and even price of the stuff can be ridiculous in small quantity.
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Re: Why use plywood?

Postby rruff » Wed Mar 01, 2017 12:53 pm

JaggedEdges wrote:Let me tell you about modern composites, they have most of the resin sucked out of them by vacuum, then are oven cured. if you don't have the means to do that, you end up with heavyweight sh** that was just nasty and smelly to make.


:thinking: Eh? People do hand layup of fiberglass all the time without vacuum or oven cure.
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Re: Why use plywood?

Postby JaggedEdges » Wed Mar 01, 2017 1:24 pm

rruff wrote:
JaggedEdges wrote:Let me tell you about modern composites, they have most of the resin sucked out of them by vacuum, then are oven cured. if you don't have the means to do that, you end up with heavyweight sh** that was just nasty and smelly to make.


:thinking: Eh? People do hand layup of fiberglass all the time without vacuum or oven cure.

They do, yes, doesn't mean they've done the lightest job. Cheaper resins are like 50-80lb a cubic foot. Plywood around 30 a cubic foot for comparison. Use 2 layers of cloth, home use technique (Mad squeegee skillz) and you'll probably make something 1/8 thick and weighing 20lb or so for an 8x4 area, when 1/8 lauan weighs 10lb a sheet.
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Re: Why use plywood?

Postby aggie79 » Wed Mar 01, 2017 1:31 pm

tony.latham wrote:
why use it if it is so heavy and prone to rotting and delaminating.
:thinking:

Huh? A camper made from a high-grade exterior plywood will last many generations if the wood is sealed from moisture (preferably with epoxy) and protected from UV rays.

And it doesn't have to be heavy.

Plywood. :thumbsup: :applause: :thumbsup:

Tony


Tony,

Thank you for jumping in on the discussion. My teardrop construction is very similar to the way you built your teardrops with plywood "framing", aluminum skin, etc.

From some of the conversations on this thread it would seem that, at almost ten years old, my teardrop should be delaminated, rotted, decomposed, and growing mushrooms and fungi around all of the leaky aluminum skin seams and joints.

And about the weight. Oh my goodness. I guess I was either dreaming or hallucinating about towing my teardrop for a couple of years with a four-cylinder Honda CR-V with a 1500-pound tow rating. If I can find a way to see underneath the now organic slime that was my teardrop, I need to check to see if my de-rated to 1400-pound, #9 Torflex torsion axle has collapsed. Surely it must have, because there is no way a 5' x 10' x 4' plywood and aluminum teardrop can weigh less than 1400 pounds loaded.

Actually my teardrop has held up fine, does not leak, and is a reasonable weight.

Take care,
Tom
Last edited by aggie79 on Wed Mar 01, 2017 5:11 pm, edited 1 time in total.
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Re: Why use plywood?

Postby rruff » Wed Mar 01, 2017 1:50 pm

JaggedEdges wrote:They do, yes, doesn't mean they've done the lightest job. Cheaper resins are like 50-80lb a cubic foot. Plywood around 30 a cubic foot for comparison. Use 2 layers of cloth, home use technique (Mad squeegee skillz) and you'll probably make something 1/8 thick and weighing 20lb or so for an 8x4 area, when 1/8 lauan weighs 10lb a sheet.


I don't even get 1/8" thickness with two layers of 1708 cloth (and that will be a lot stronger than 1/8" luan), so I don't know what cloth you are referring to.

I've been experimenting with FG layups, plywood, and PMF. FG and PMF are both inherently denser than plywood, but the FG at least is much stronger as well. The industrial methods to maximize the strength of FG make it a bit better, but hand layup works fine.
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Re: Why use plywood?

Postby greygoos » Wed Mar 01, 2017 1:55 pm

Bravo to Aggie- Tom. Well said!!!
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Re: Why use plywood?

Postby mgb4tim » Wed Mar 01, 2017 2:46 pm

Do you use a vacuum, or just roll it out?

The current roll of 1708 I have is 5' wide. Been thinking of making a sample side wall under a vacuum. I'd lay it out flat on waxed MDF cut to shape. Use split pool noodles with 2 layers of 1708 over them to create ribs on the inside for rigidity - maybe 16' centers. I think a layer of gelcoat, a layer of 3/4 oz chopped, then 2 layers of 1708 would be more than adequate. If I could prop the ends of the mdf on flat 2x4s, and let the center sag, the resulting curve might even add some rigidity when coupled up the the roof and floor. I use laminating poly resin for the car parts I make, but, might consider epoxy for this. I'll lose the benefits of the laminating resin using the vacuum.

Might have to make that sidewall to see what it weighs.

rruff wrote:
JaggedEdges wrote:They do, yes, doesn't mean they've done the lightest job. Cheaper resins are like 50-80lb a cubic foot. Plywood around 30 a cubic foot for comparison. Use 2 layers of cloth, home use technique (Mad squeegee skillz) and you'll probably make something 1/8 thick and weighing 20lb or so for an 8x4 area, when 1/8 lauan weighs 10lb a sheet.


I don't even get 1/8" thickness with two layers of 1708 cloth (and that will be a lot stronger than 1/8" luan), so I don't know what cloth you are referring to.

I've been experimenting with FG layups, plywood, and PMF. FG and PMF are both inherently denser than plywood, but the FG at least is much stronger as well. The industrial methods to maximize the strength of FG make it a bit better, but hand layup works fine.
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Re: Why use plywood?

Postby JaggedEdges » Wed Mar 01, 2017 2:50 pm

rruff wrote:
JaggedEdges wrote:, but the FG at least is much stronger as well. The industrial methods to maximize the strength of FG make it a bit better, but hand layup works fine.


Well yah, but you get more strength with same weight of ply too. Just saying hand layup isn't gonna be wayyyyy much lighter than intelligent use of ply.... and you have to build it twice for a one off, i) build thing in shape of thing you want to build, ii) glass over it to actually make it.

It tends to come into it's own for complex shapes that you need way more wood to whittle away to make or complex supporting structure for thin veneers. With glass you lose all that excess structure and the compound shape self supporting when you take it off the mould, but other than that it's a pain in the neck, especially for larger flatter areas you need to build ribs into or it's gonna flop around or drum like a biatch. You can end up with things that are strong but floppy, it might be optimal strength but optimal rigidity doesn't have your windows popping out trundling down the road. So for that, i many of those "strong" materials you end up using twice the optimum, while boring old plywood with it's natural damping and bulk rigidity has it built in.

For the absolute optimum use of strong materials being some envelope that doesn't fly apart going down the interstate you can probably have 3 pounds of mountaineering tent with carbon fibre poles and ripstop nylon designed to resist 160mph winds, nailed to a flatbed, but it's not really the solid feeling roof most tear builders are looking for.
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Re: Why use plywood?

Postby rruff » Wed Mar 01, 2017 3:33 pm

mgb4tim wrote:I think a layer of gelcoat, a layer of 3/4 oz chopped, then 2 layers of 1708 would be more than adequate. If I could prop the ends of the mdf on flat 2x4s, and let the center sag, the resulting curve might even add some rigidity when coupled up the the roof and floor. I use laminating poly resin for the car parts I make, but, might consider epoxy for this. I'll lose the benefits of the laminating resin using the vacuum.


No vacuum for me! I've been playing with test pieces of 15 psi XPS (blue or pink foam), textured with a carpet seam roller. First I make a paste of epoxy and silica powder and spread it over the foam to fill the texture, then layup the cloth and epoxy (same batch of epoxy) and roll it with a bubble buster.

For the exterior skin I think one layer of 1708 and one of 10 or 6 oz cloth is about right. Weighs .45-.50 lb/sq ft IME. And a 48"x6"x1" sandwich of that and foam sagged a little over 1/2" while holding up 3 28 lb concrete blocks in the center. I'm not going to eliminate wood in mine, I'm just trying to get away from the external plywood skin. The inner skin will be 3mm okoume, with 1" of foam and redwood stringers (~16" spacing) in the middle.

The chopped matt will give you more thickness, but it isn't very strong at all. Epoxy generally doesn't dissolve the binder either (chopped matt is made for polyester resin). 1708 has a matt layer anyway. I've been playing with bulking matt also, and I think that is a better way to get more thickness and stiffness in the piece. It is some sort of cloth with microspheres inside and you can get more thickness with less weight. But I don't think it's ideal to make a separate skin that you just need to attach later. If you are using epoxy anyway, might as well lay it up on the foam.
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