Bendy Birch Trouble

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Bendy Birch Trouble

Postby mjewell5 » Wed Nov 18, 2015 1:24 pm

Hello all:

I am in the middle of building my tear, a modified Grumman II. 9' long by 5' wide by 5' high with about 7" of underbed storage.

Last weekend I began skinning the interior using 1/8" bendy birch. It's not a plywood, but looks to be a single ply of shaved birch. It came in 4 X 8 sheets. My ribs are spaced anywhere from 12 to 20", and I glued the sheeting to each of the spars and got pretty good adhesion to all of the ribs. After a couple of days I noticed the sheeting was starting to get sort of "wavy" between the ribs. It seems like the bendy wood has pretty good strength across its width, but not so much with the grain.

My question is, how the heck should I fix it? My first thought is to brace it flat from inside, then glue some of the same wood to the outside of the skin with the grain perpendicular to the interior skin. Should this be enough to get the interior skin to hold its shape better? I hate the thought of pulling it all apart to start over and skin it with plywood, so I am hoping someone hear has experience with this type of wood.

Any help would be much appreciated. I will post a few pictures when I can.
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Re: Bendy Birch Trouble

Postby halfdome, Danny » Wed Nov 18, 2015 2:01 pm

I don't get it, you say it's not plywood so I'm to assume it's 1/8" veneer?
Plywood has veneer pieces glued together in alternating directions and is very stable.
Veneer is raw wood with no structural support and will mimic the surface it's applied to.
Giving we have moisture on this planet wood absorbs moisture and will expand and contract depending on the humidity.
If you applied it without full structural support then it will get wavy in the areas of no support, because it's very thin wood.
There's not much that can be done once it's glued on.
I would leave it in place and glue 1/8" Baltic Birch Plywood over it.
:D Danny
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Re: Bendy Birch Trouble

Postby KCStudly » Sat Dec 05, 2015 9:09 am

I wonder if you could stabilize it by gluing in hard foam insulation above the ceiling (assuming that you have not skinned the outside yet and plan to insulate). This might give it a faceted look, tho. Otherwise, I agree that what Danny said about leaving it and adding another layer of ply sounds like the best solution; that should follow the profile nice and smoothly.
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Re: Bendy Birch Trouble

Postby Woodbutcher » Sat Dec 05, 2015 4:26 pm

If you can still add in a few ribs from the inside I would try that first. Twenty inches is to far apart on a bend. Plus what you have has no strength to it. Adding 1/8 baltic birch will help but you need to level out the surface first or the new 1/8 will just follow the old roof over time. I have used what you are referring to on curved bar fronts. After kerfing the front to bend we would use the "bendy sheet" you have to cover the kerfs. Then we would veneer or laminate over the bendy. That stuff is not really meant to be structural.
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Re: Bendy Birch Trouble

Postby Squareback » Fri Dec 25, 2015 12:01 pm

Bendy birch has no structural integrity and is meant to be bent over an existing substrate like a 3/8 - 1/2 bendy luan. The luan is a very nasty looking bendy board and the 1/8 inch birch is meant as the finishing touch. Your ribs would need to be around 4 to 6 inches on center max and I'm still not sure if this would prevent the waviness you are experiencing. Being so thin the wood would be extremely sensitive to variations in humidity and would react rather quickly to varying conditions. You might be able to place it in the sun or a heated garage and cook off the moisture which would cause the wood to shrink and tighten up possibly removing the waviness. You would need to seal it both outside and inside to prevent moisture from getting back in and hopefully prevent the waviness. Hope this helps and good luck.
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Re: Bendy Birch Trouble

Postby mjewell5 » Sun Jan 10, 2016 9:34 pm

UPDATE: I found a source for 1/8" Birch plywood! It looks like a cabinet veneer, and comes in an A/C finish. It is VERY stable around bends, and worked very well for the inside radius of my galley hatch. I used another 1/8" ply on the outside of the hatch, sort of a reddish looking wood, not sure what it is called. It, too, is very stable being a plywood, and will work very well on the outside of the TD. I plan on covering the entire thing in 4 or 6 oz glass cloth, then coating and smoothing with West System Epoxy. After that, I will paint with a marine paint called Interlux Perfection. It is a 2 part marine paint that is harder than woodpecker lips and wears like iron. I painted my sailboat with it, and found it to be extremely durable. Any scuffs or scrapes buff right out.

As for the bendy Birch waviness, I built a forward cabinet to stow blankets and such, that will cover the worst areas. I was able to satisfactorily fix most of the other areas to the point that I can live with them.

One thing I have discovered about building my own TD is that I really underestimated both time and money. I told my wife I could build one for around $2500. Yeah, right, maybe if I more than double that amount! To be fair, I have not really spared much expense. I figure that I will finish this one and use it for a couple of years, the whole time making notes about what I would do different. Then, in 3 or 4 years build version 2.0, with all of the mods I'm sure I will need to make. The other thing I found is that this is a blast! It's been awhile since I was able to use all of my wood working tools, and good to see I still know my way around a saw!
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