Bending Plywood

[Irving]

I apologize if this has been gone over thoroughly. I couldn't seem to find a good thread though.

I am using 5.5 mm (7/32") plywood on the exterior. Despite being quite thin, it does not seem to want to bend on it's own to fit my teardrop shaped camper. It is going to need to be bent slowly - possibly using water (hot wet towels) and heat with ratchet straps.

I am concerned about water having a bad effect on the plywood.

How have some of you had success with your tight curved areas and bending the plywood to fit?

This picture shows the areas that will need to be bent.

[KCStudly]

The front seems "reasonable" but on the tight side. The peak at he top where the rear slope meets the flat roof looks like an extremely tight problem area. You may want to soften that up in order to get it to curve, or make it into a miter.

Personally, I prefer the gentle arch to the abrupt peaks.

[DMcCam]

Hi Irving, We used 1/8" Baltic Birch plywood and it took the shapes without too much trouble but almost 1/2", that's not going to bend much. The 1/8" ply has a grain to it so it bends one direction quite easily. 1/2" has an opposing grain that is very stiff. I've heard of members bending 1/2" with the wet towel method and such but it seems like 2 layers of 1/8" would be much easier. May I ask why you want to use such heavy plywood? We glued thee 1/8" ply over stiff insulation and the roof spars; it became very strong. Then we glued too thick 0.063 anodized aluminum on top of it. I'm sure I could practically tap dance on it.

Cheers,

Dave

[Irving]

Hi Irving, We used 1/8" Baltic Birch plywood and it took the shapes without too much trouble but almost 1/2", that's not going to bend much. The 1/8" ply has a grain to it so it bends one direction quite easily. 1/2" has an opposing grain that is very stiff. I've heard of members bending 1/2" with the wet towel method and such but it seems like 2 layers of 1/8" would be much easier. May I ask why you want to use such heavy plywood? We glued thee 1/8" ply over stiff insulation and the roof spars; it became very strong. Then we glued too thick 0.063 anodized aluminum on top of it. I'm sure I could practically tap dance on it.

Cheers,

Dave

I don't know where you are getting 1/2" from. I'm using 7/32" plywood as I stated. That's 1/32" less than 1/4".

[aggie79]

To bend around those small radii will be tough with 7/32 plywood. If your plywood has a solid core and not multiple laminations I don't think it can be done. It's expensive to waste a sheet of plywood but you may want to try a test bend first before you try installing it in your camper.

[Irving]

My main concern is damaging the plywood from getting it wet. I think I have a good shot at bending around those areas using hot wet towels and a propane heater and slowly closing ratchet straps. Should I be concerned about getting the plywood wet? Will it de-laminate?

[S. Heisley]

Slowly clamp it down. Once you get it all the way against the spars, let it sit overnight or at least a day. Then, remove the clamps on one lengthwise end and apply your glue (Titebond II or III is best) the entire way and then, using the boards and clamps, clamp it back down. Let it dry before trying to do the other lengthwise end the same way. You can add in few screws for good measure, along the way, if you want.

Since I had just enough for one layer of plywood, I backed mine with fiberglass and epoxy resin to further support the curve. All this has served me well, so far.

[S. Heisley]

Before I forget about it, I wanted to mention something else about the picture that I posted in that last post.
You'll notice that the upper support boards that the clamps are using are wrapped in waxed paper. This keeps those removable boards from becoming glued to the permanent wood. Since the plywood only extends part way across the underneath spar, when it is glued down, the titebond glue will squeeze out some and the temporary upper board might become glued in place without the waxed paper intervention. You will butt your other plywood against the curved piece at the spar and fill and sand the small joint crack after. Hope this helps.

[TPMcGinty]

I used bending plywood. Plywood designed to bend around a tight radius. It worked well.

[S. Heisley]

I used bending plywood. Plywood designed to bend around a tight radius. It worked well.

Good Point. I never have found that. Where do you get it?

[halfdome, Danny]

I used bending plywood. Plywood designed to bend around a tight radius. It worked well.

It's not meant for exterior applications like teardrops.
I've used it in many radius store fixtures and reception desks and it's really a poor quality plywood with the grain going the 4' direction.
It's usually covered up with plastic laminate (plam) or a backed veneer and it's only intended purpose is for interior applications.
I still have a couple sheets in my plywood rack and would never put it on a teardrop.
It's best to use layered & glued 1/8" Baltic Birch plywood.
You get what you pay for.
Danny

[Irving]

Here are some photos from my test bend. As you can see, I am using ratchet straps around 7/32" plywood that is covered with soaked towels. I put this right in front of the woodstove and set up a propane heater as well so that it was surrounded with heat. You can literally see the steam flying. As it warmed up, I slowly cranked the ratchet straps tighter and tighter. I then set it outside to cool before removing the straps. Several hours later, the test peice is holding it's new bent shape and shows no signs of de-lamination.

[S. Heisley]

That was a trick question, Irving, wasn't it. You got your plywood to curve!
Congratulations on winning the plywood curving dilemma that you said you had.
It looks like you have access to a very nice shop, too! You are most fortunate.

[jeff0520]

I used the very same plywood on the Command Post. My bends aren't as tight as yours, and it should be noted I'm a BIG ol' boy, 6'2" and 300 pounds, but I just used my body weight to bend the plywood into place.


I just glued and screwed the leading edge into place, applied glue to all the spars, and leaned on it. then I screwed the plywood to the next spar. then I leaned on it a little higher, and screwed it down.


Granted, most people aren't a big fat land monster like me, so your results may vary. In my defense on the big fat land monster part, I will point out that I can bench press my body weight, so big I may be, but I'm not a couch potato

[Irving]

Backed my jumbo teardrop up to the raging woodstove and busted out the propane heater. Wrapped soaked towels over the plywood, let it get nice and hot for 15 minutes or so and started cranking the ratchet straps. It won't say it was easy or that it didn't take a few hours. But I now know that 7/32" plywood can be curved around some tight radius areas if you want it to. I was fortunate enough to not inflict a single crack to the plywood either.