Why use plywood?

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Re: Why use plywood?

Postby QueticoBill » Wed Mar 01, 2017 5:04 pm

Second bravo for Aggie's well stated comment. "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." I was thinking similar and wondering if there really were a lot of reports of rotting plywood. I don't do real well with the search function here but could not find the purported epidemic of rotting wood tears.

As far as weight, wood strip canoes - albeit glassed - are often lighter than aluminum and around the weight of some kevlar. And if wood is heavy, google concrete canoes. I'd hate to portage those beasts.
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Re: Why use plywood?

Postby alchemist77 » Wed Mar 01, 2017 5:29 pm

LOL concrete canoes! What a spirited debate. It answers a lot of construction questions I have. I thought of 3mm okumi plywood and foam, cedar strip or spruce strip w\fiberglass. Same thing as building a strip canoe with insulation. What about using strip construction inside and out with foam?

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Re: Why use plywood?

Postby rruff » Wed Mar 01, 2017 7:46 pm

QueticoBill wrote:wondering if there really were a lot of reports of rotting plywood.


viewtopic.php?f=2&t=49207 Might be lots more, that's just one I know of. If you search google you'll find many links.

It isn't necessarily an issue, but I'd definitely make sure that the design does not have seams that could leak.
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Re: Why use plywood?

Postby tony.latham » Wed Mar 01, 2017 9:13 pm

rruff wrote:
QueticoBill wrote:wondering if there really were a lot of reports of rotting plywood.


viewtopic.php?f=2&t=49207 Might be lots more, that's just one I know of. If you search google you'll find many links.

It isn't necessarily an issue, but I'd definitely make sure that the design does not have seams that could leak.


That cited post isn't about rotting plywood. It's delamination. That's one reason I won't touch luan. It's made for interior use.

I've tested ACX, Baltic birch, and 1/4" underlayment––the plywoods I use––by throwing raw scraps in a bucket of water. I throw the water out after three generations of mosquitos and there is no deamination.

Now... OSB... there's some junk.

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Re: Why use plywood?

Postby noseoil » Wed Mar 01, 2017 10:36 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."

Gator, you just have to use good design & construction sense on any type of build, regardless of the material type. Plywood is fine, foam is fine, kevlar panels are fine, but they're bit more spendy to work with & difficult to master. It just boils down to budget, time, tool investment & individual manual literacy. Knocking plywood construction is like knocking foam construction, it's pointless.

Looking forward to your build.
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Re: Why use plywood?

Postby tony.latham » Wed Mar 01, 2017 11:10 pm

Knocking plywood construction is like knocking foam construction, it's pointless.


Amen, bro... :thumbsup: You can sure tell when it's the off-season.

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Re: Why use plywood?

Postby Andrew Herrick » Thu Mar 02, 2017 12:26 am

Gator417 wrote:So most use plywood because it is easy to work with, relatively inexpensive, easy to find and people are familiar / comfortable with it. Its convenient. That's pretty much what I figured, but I wanted some feedback from the experts. Plywood is anything but light though. Its probably the heaviest material one could possibly use in building a camper. Not to mention its not used, structurally, by any camper manufacturers. It seems like some folks here have never considered using anything but, while others would never consider using it at all. Very interesting. Thanks for the speedy responses. Fwiw, I'm planning on using foam and laminating it with tyvek or maybe nylon (tent fabric) and possibly covered with frp. Still being drawn out in my head movies though.
Thanks again,
Gator


Couple things to point out here. First of all, the world of teardrops is always ripe for innovation, so charge ahead!

But I think there are a few misconceptions here.

1. Is plywood heavy? Sorta. Sure, I can pay $250 for a 3/4-inch nautical polyurethane foam that weighs half as much, but that's ... what ... 25 pounds per wall? Or I can pay $50 for 1/8-inch Adzel that weighs 40% as much as 1/8-inch ch, but that's ... 5.5 pounds saved?

Now, these advanced materials certainly have their place. They're strong, waterproof and lightweight. And when every pound counts, they're worth the price premium. But most people aren't looking to shell out an extra $400 - $1,000 in materials to save 10-15% total weight, and I don't blame them. Most cars can tow 1,500 pounds, and a medium-sized plywood+aluminum teardrop weighs half as much.

2. Is plywood used structural by any camper manufacturers? Almost all use plywood, OSB or dry-OSB for subfloors. No, solid plywood isn't used for wall sheathing, but that's because weight savings matter in a 32-foot-long camper. Cheap stick-and-tin RVs don't even have wall sheathing; just aluminum skins.

3. I'm all for composite and laminated designs. Keep researching! But the issue comes to manufacturing capability - most people don't have the vacuum presses required to properly laminate fiberglass and other exteriors - and cost. Filon, the most popular choice for FRP, can cost as much as the rest of the teardrop put together.

Now, if everyone had the extra $2,000 to pay for nautical board construction, I'd be using that, instead! But in the real world, if something works for its application, why replace it with something 3x as expensive?
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Re: Why use plywood?

Postby Gator417 » Thu Mar 02, 2017 5:12 am

Yes, Andrew, many misconceptions here.
Like I said, nobody using plywood structurally. These campers have steel underpinnings, just like TDs, and the floor rests on the steel.
Not sure where you get $250 for sheets of foam, but I'm happy to sell you as much as you want for half that, since I get it for $15 for 1/2" & $25 for 1".
The facts are plywood just won't hold up to the elements like synthetic materials, and its substantially heavier. You can make it lighter with cutouts, but it won't be nearly as strong and with all the increased surface area, will be much more prone to damage by moisture.
As I and others have said before, the strength come from the structure, the design, rather than the choice of materials.
Most people are using plywood either because everyone else is or because they just don't know of other options or they don't know how to use the other materials. Good enough answer for me.
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Postby kokomoto » Thu Mar 02, 2017 7:32 am

Gator417 wrote:Yes, Andrew, many misconceptions here.
Like I said, nobody using plywood structurally. These campers have steel underpinnings, just like TDs, and the floor rests on the steel.
Not sure where you get $250 for sheets of foam, but I'm happy to sell you as much as you want for half that, since I get it for $15 for 1/2" & $25 for 1".
The facts are plywood just won't hold up to the elements like synthetic materials, and its substantially heavier. You can make it lighter with cutouts, but it won't be nearly as strong and with all the increased surface area, will be much more prone to damage by moisture.
As I and others have said before, the strength come from the structure, the design, rather than the choice of materials.
Most people are using plywood either because everyone else is or because they just don't know of other options or they don't know how to use the other materials. Good enough answer for me.
Gator


Post a question, watch experienced TD builders answer it, then attempt to enlighten them with your superior intellect and knowledge. What was your original question?
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Re: Why use plywood?

Postby JaggedEdges » Thu Mar 02, 2017 8:23 am

kokomoto wrote:Post a question, watch experienced TD builders answer it, then attempt to enlighten them with your superior intellect and knowledge.


Yeah, I never knew plywood = lead and you're obligated to use massive slabs of it so OPs assertion of "heaviest material you can possibly use" is proven. Even then using slabs it's still NOT. THAT. HEAVY. 8x4 boxdrop from 1" 1/16 slabs is gonna be 80lbx5 = 400lb on top of maybe 300lb trailer. 700lb, and by the time you've done that, you could probably block under the frame and set an SUV on top of the thing and it would hold up.

I was reading about materials for boatbuilding and the author of that piece said something like, "you can make a overweight ungainly pig out of anything if you do it wrong." Then he mentioned a racing boat that was oak frame and ply planked with thin epoxy sheathing and said you'd be hard pressed to do better with carbon fibre.


Edit: BTW if I thought RV manufacturers were in any way shape or form "right" about anything, I wouldn't be here. Neither would most people. They went off on the path of stupidity some time in the late 80s, so here we are, making what we want.
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Re: Why use plywood?

Postby noseoil » Thu Mar 02, 2017 8:50 am

"Most people are using plywood either because everyone else is or because they just don't know of other options or they don't know how to use the other materials. Good enough answer for me." Gator

Gator, just an FYI. Your comment smacks of the "American people think" type of comment in politics, which is completely wrong in many instances. The "most people" type of statement leaves a particularly sanctimonious stench behind when I see it in print. Your tone is condescending, your comment is particularly odious. Please allow me to elaborate.

I have worked as a cabinet maker in commercial, residential, aircraft & marine work. Before retiring, I worked in the custom home manufacturing segment of the economy, as an "estimator" in a roof truss plant. Most of my duties there dealt with the structural design, manufacture & estimating cost of complex shapes in 3D roof design & load path analysis. It was 8 hours a day of computer analysis in design, cost & production, but I'm no engineer.

I had many options for my build, but I chose plywood for its structural & finish requirements. Having worked with Nomex, Kevlar & balsa-core panels in the aircraft industry, I still chose plywood as the best option for weight, strength, cost & its simplicity of manufacture. It doesn't "rot" unless the design or execution is poor. It isn't heavy, unless its use in scantlings is completely misunderstood. A Nomex & Kevlar honeycomb panel which is 3/8" X 40" X 100" costs about $1,000. It would be much lighter to use for a build. It would add a bit to the cost, though.
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Re: Why use plywood?

Postby Andrew Herrick » Thu Mar 02, 2017 9:38 am

Gator417 wrote:Yes, Andrew, many misconceptions here.
Like I said, nobody using plywood structurally. These campers have steel underpinnings, just like TDs, and the floor rests on the steel.
Not sure where you get $250 for sheets of foam, but I'm happy to sell you as much as you want for half that, since I get it for $15 for 1/2" & $25 for 1".
The facts are plywood just won't hold up to the elements like synthetic materials, and its substantially heavier. You can make it lighter with cutouts, but it won't be nearly as strong and with all the increased surface area, will be much more prone to damage by moisture.
As I and others have said before, the strength come from the structure, the design, rather than the choice of materials.
Most people are using plywood either because everyone else is or because they just don't know of other options or they don't know how to use the other materials. Good enough answer for me.
Gator


Spirited conversation we have here :) Lots of good information coming forth. Thank you for your questions.

1. Like I said, the structural use of plywood in a stick-and-tin camper seems a non-issue ... stick-and-tin campers get their wall strength, what little they have, from the framing and skinning. And I don't think you can successfully laminate fiberglass or other synthetics over plywood due to expansion rate differences. So, while you're right that plywood isn't used much in RV superstructures BESIDES the subfloor and interior paneling, that doesn't seem to be an argument against the quality of plywood itself ... I mean, when was the last time a mainstream RV was considered a bastion of quality? :?

2. $15 foam isn't what I'm talking about. That's probably rigid building foam, and it won't hold fasteners worth anything, and it's not UV-resistant, and it has yield strengths an order of magnitude less than wood. I'm talking about Coosa board and the like, polyurethane foams that are intended to be near direct substitutes for plywood.

3. Weight seems to be a big concern here ... but I'm not understanding why? We're not building rockets. We're building teardrops. It's not uncommon for 2/3 to 3/4 the weight of a camper to be in the chassis and features, not the shell. For most people, saving 100 pounds will have no measurable impact on towing capacity or fuel savings.

4. "As I and others have said before, the strength come from the structure, the design, rather than the choice of materials." - Well, um, yeah ... sorta ... but you can't use that as a blanket statement to justify all other, possibly weaker materials. Stress is stress, no matter what material bears it.

5. Again, I'm not saying you shouldn't go for glory! :thumbsup: Synthetics are awesome. Seriously. But preferring one doesn't mean the other is useless. Besides, synthetics have their own issues. Most semi-structural plastics, like HDPE, don't glue well. And most honeycomb panels don't hold screws or play well with bolts.

Lastly, let's remember that the teardrop revolution started as a grassroots movement, a rebellion against consumerism, a bunch of people from all backgrounds trying to find freedom on the road with their bare hands, and they used what was available to them. And their basic designs have worked well for, oh, about 80 years now. Lots of people on this forum are doing the best they can to build their first camper with a jigsaw and a bottle of wood glue, and I think that deserves respect from all of us. *end of sermon*
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Re: Why use plywood?

Postby aggie79 » Thu Mar 02, 2017 9:45 am

Gator417 wrote:OK, I've never built any camper.


Most of us on the forum had never built a camper before either and felt very fortunate to have found this forum where we could learn from the experiences of others on methods of construction and techniques that are relatively easy to build even for someone without construction experience using readily available common materials and reasonable number of power tools, and that will result in a safe, reasonably lightweight and comparatively inexpensive camper.

Gator417 wrote:As I and others have said before, the strength come from the structure, the design, rather than the choice of materials.


It's been about 40 years since I took structures, statics and dynamics, and materials classes in college, but back then different materials had differing structural properties that had to be accounted for in structural design. Maybe things have changed and structural design now is the same for wood, metals, composites, plastic, etc.

Gator417 wrote:The facts are plywood just won't hold up to the elements like synthetic materials, and its substantially heavier.


Please direct us to the facts. I'd like to see them. The walls of my house are sheathed in plywood, and so is the roof deck. Our house is 33 years old and is still standing. My teardrop is constructed to much closer tolerances with much better weatherproofing than my home so I would expect it to last at least as long as the house.

Gator417 wrote:You can make it lighter with cutouts, but it won't be nearly as strong and with all the increased surface area...


I guess I need to recheck my math but I'm pretty sure that my plywood "framing" has less surface area than the overall sidewall area. (The picture below shows the plywood framing with the interior wood finish applied to the framing. Not shown is the 3mm plywood "skin" that was applied over the framing.)

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Gator417 wrote:You can make it lighter with cutouts, but it...will be much more prone to damage by moisture.


Huh?

My plywood framing was covered with a 3mm plywood skin. 2 coats of epoxy were applied to the skin.

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Then the aluminum sheeting was applied with a bead of sealant around the perimeter and openings and along overlapped seams. The sealant was 3M 4200 marine sealant rated for below waterline use.

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After the sealant was set, the exposed screws were removed, sealant was injected into each screw hole, and the screws were replaced.

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Where trim was used it also was bedded in sealant.

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I admittedly went overboard in my efforts to have a water-tight teardrop shell. There are many other approaches and techniques that can be used to accomplish the same goal.

In the end, I ended up with a weather-resistant teardrop weighing a little over 1200 pounds. I have no doubt that I could have built it less than 1000 pounds if I had used lighter components (wheels, tires, fenders, etc.) and material finishes (mosaic glass tile counter, oak cabinets, etc.) if weight was my focus instead of appearance.

Take care,
Tom
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Re: Why use plywood?

Postby rruff » Thu Mar 02, 2017 2:33 pm

Gator417 wrote:Like I said, nobody using plywood structurally. These campers have steel underpinnings, just like TDs, and the floor rests on the steel.


:thinking: I've used and will use plywood structurally, for a truck camper that mounts directly to the frame. No steel needed. The plywood serves as the skins on a foam and wood-stringer core. It makes a very stiff and strong platform. Frankly I don't understand why everyone builds a steel frame and then bolts their floor to it. Better to make the floor structural and bolt the tongue and wheels to it.

Your contention that "plywood is heavy" is about 180 degrees from the truth. Rather it's one of the lightest structural materials. That makes it a great material for the skins in sandwich construction when you are using light (cheap) foam in the core. The low density means you can make the skin thicker compared to fiberglass or aluminum, which makes the skins stiffer and resistant to denting and cracking.

Plywood's only real downside is the potential for delamination and rot.
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Re: Why use plywood?

Postby IndyTom » Thu Mar 02, 2017 3:20 pm

[quote="aggie79"
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.
[/quote]

Extremely well said!
I am building with wood because I love working with wood. Wood is relatively light, strong and very easy to work with, and with proper construction techniques, virtually immortal. I hold a Master's Degree in Wood Science and Technology, and I can assure you that delamination and rotting are problems with construction, not problems with the material. With the proper protection, wood will last indefinitely. It is only when you allow wood, ply or otherwise, to come into contact with an environment with which it is not compatible, that you experience issues. So any builder who is not willing to do what wood construction requires, please go find another material to build with. I have seen enough shoddy wood construction to last me a lifetime.

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