plywood for holding tank

JSmith · Post by **JSmith** » Sun Mar 02, 2008 2:07 pm

I plan to use 1/4" plywood for a stitch & glue holding tank- about 30 gallons. Do I need to use "marine" plywood? I have the gougeon book and they say high quality but I wonder if that is just for hulls or all projects.

Thanks, Jon

Hirilondë · Post by **Hirilondë** » Sun Mar 02, 2008 2:39 pm

If you really need to use 1/4" ply I would use marine, or at least a product with no gaps in the plys. You need the strength. If your willing to go thicker you can use almost anything. You will be saturating and coating the whole thing in epoxy anyway.

The Good Goose · Post by **The Good Goose** » Sun Mar 02, 2008 5:51 pm

I built a stitch and glue tank out of 1/2" baltic birch and it seemed fine. Baltic birch is nice in that it has a lot of plys. I figured with it being saturated with epoxy and cloth it didn't need rot resistance. Make sure to put baffles in a 30 gallon tank. I think as long as there are baffles 1/4" should work fine. I would try to use Baltic birch or marine grade to get the extra plys. It is a lot stronger.

Brock

Quetzalsailor · Post by **Quetzalsailor** » Mon Mar 03, 2008 10:03 am

Perhaps you might think of the plywood solely as core. It could be almost any junk* with adequate ability to transmit shear, presuming you encapsulate it. I think the tough part would be getting fiber across the ends/edges of the panels before assembly; I've never liked the discontinuity at the corners of a stitch and glue. Bad enough on a dinghy, but you can get to the interior.

Important to remember that epoxy really doesn't saturate the core. WEST ain't really true. It works because it bonds well to wood and has a very low permeability.

I presume you're making this thing because you want an odd shape that you cannot buy reasonably. Figure out how to convince yourself that your shape is not too extreme to resist undue flexure.

Baffles are nice, but I wonder about 'em in a sewage tank. I don't think my plastic 30gal holding tank has any.

*Luan underlayment

Peter · Post by **Peter** » Tue Mar 04, 2008 1:15 am

I have a plywood/epoxy tank.
I built it from exterior grade 1/2" plywood with triangular blocking on the insides of all the joints. It's epoxy and cloth inside and out, and the back conforms to the shape of the hull.
It sits on a shelf, held in place with a frame in front. There's clearance all around to allow for flexing of the bulkheads on either side.

It was a lot of work, but the material cost was low and it should last a long time.

JSmith · Post by **JSmith** » Wed Mar 05, 2008 8:01 am

When/if the snow & sleet stop I'll make a run to Westbrook for some marine plywood. Seeing how it's the honey tank I'll go on the heavy side.