Thread: Does plywood always bow?

No ply should bow or twist, its usually poor storage practices that does the damage... I would not accept it especialy at $400 per sheet

Yeh, what Harry said specially on the thicker stuff, thin stuff will move more but still should be flat if stored flat


Pete

Thanks guys.

I exagerated the bow a bit - last night I measured it and it's about 8mm. But still very visible. And no amount of clamping I would say will get that bow out.

It's annoying. The ply is well stored at Mr Plywood. The racking is good and the 32mm, which hardly anybody would buy, is stored well out of reach.

My theory is that perhaps the top sheet that has no weight on it takes in moisture on the exposed upper face which causes it to bow (I'm floundering here and just making this up).

Maybe next time I tell them I want one of the sheets out of the middle of the pile?

Originally Posted by scottbr

Thanks guys.

I exagerated the bow a bit - last night I measured it and it's about 8mm. But still very visible. And no amount of clamping I would say will get that bow out.

It's annoying. The ply is well stored at Mr Plywood. The racking is good and the 32mm, which hardly anybody would buy, is stored well out of reach.

My theory is that perhaps the top sheet that has no weight on it takes in moisture on the exposed upper face which causes it to bow (I'm floundering here and just making this up).

Maybe next time I tell them I want one of the sheets out of the middle of the pile?

You are probably right about the top sheet absorbing moisture on the top and that causing the bow. I have seen places where they keep a sheet of MDF on top of all plywood stacks.

They should give you a flat sheet, especially 32mm! What else are they used for apart from doors and table tops which should be perfectly flat.

I bet they will love getting a sheet out the middle of the stack for you...

I've spent about $3,000 there in the last couple of months, so I'm sure they'll be accomodating.

Here's another possibility: When they take a log out of the steam chest and spin it on the lathe, the veneer has a top & bottom (really an outer face and an inner face.) If all the layers remain that way, cross-grained orientations and no amount of pressure in the glue press can stop the sheet from cupping to some degree.

North Central Plywood in Prince George BC made 145 sheets of 18mm/3/4" spruce plywood in one shot. The process was a sight to behold. Trimmed, graded and sanded, it looked flat enough. Spruce-core plywood has to be the worst for cupping. Douglas-fir core plywood is far better, especially the "marine" grade. Even stacked flat under cover they cup.
If I needed some really fancy plywood, I'd have to bite the bullet and buy lumber-core plywood or nothing.

I'm not sure how many plywood supplier options we have these days. Mr Plywood seem to have cornered the market.

I did recently buy 2 sheets of 3m x 1500mm 18mm birch ply from the US. A company here called DMK (or maybe DKM?) import them. Apparently they come here from Finland via the US. How crazy is that.

Scottbr: You may have ply that was sent to Scandinavia where the final/finish veneer was applied. Their birch is flawless I buy 1/4 sheets of Baltic birch plywood when I need smooth, flat and flawless.
I have no idea how the Americans can make and market plywood when compared with the scale of our Canadian operations.

$400 bucks for a sheet of plym I hope its as flat as marble!!

I am gobsmacked by the price of plywood, can someone tell an obviously uneducated guy why.....?

Scottbr,
need a bit more info ie what type of ply, how many veneer layers, are veneers even in thickness, do alternate veneers have opposed grain, can the glue type be identified, is there a manufacturers stamp or code colour anywhere on the sheet (stamp on the back, code colour on edge.)
There are many different causes of bowing in ply, most of which can be attributed to improper storage or faulty lay up. A common cause is multi sheet reglue to make up thicker sheets when required. Some answers to the above questions may help to make a diagnosis.

Originally Posted by scottbr

I'm not sure how many plywood supplier options we have these days. Mr Plywood seem to have cornered the market.

I did recently buy 2 sheets of 3m x 1500mm 18mm birch ply from the US. A company here called DMK (or maybe DKM?) import them. Apparently they come here from Finland via the US. How crazy is that.

I prefer to use Bruynzeel up Brookvale way

Scottbr: You may have ply that was sent to Scandinavia where the final/finish veneer was applied. Their birch is flawless I buy 1/4 sheets of Baltic birch plywood when I need smooth, flat and flawless.

The company who got those big sheets of 18mm ply for me bring it in from America. Though maybe it's Canada? We tend to lump the US and Canada together. Down the edge there was writing that said Finland.
It really is great ply - thinner layers than the usual hoop pine I get.

But the 32mm ply that bowed was just regular hoop pine presumably made here.

$400 bucks for a sheet of plym I hope its as flat as marble!!

That was my expectation, too. I thought it was a reasonable expectation.

need a bit more info ie what type of ply, how many veneer layers, are veneers even in thickness, do alternate veneers have opposed grain, can the glue type be identified, is there a manufacturers stamp or code colour anywhere on the sheet (stamp on the back, code colour on edge.)

I've never looked at it all that closely. I'll check the layers etc this weekend. I wouldn't know anything about the glue. There was a purple stamp on the back - sanded off now.

I prefer to use Bruynzeel up Brookvale way

I've heard of them. Much better range and no doubt better quality. It's a long way from the inner west, though, and traffic in Sydney is now crazy every day of the week.

I had an email exchange this week with the Chief Operating Officer of My Plywood. He was pretty responsive until I mentioned that the bowed plywood came from a Mr Plywood store. He went very quiet then.

Originally Posted by scottbr

...

I had an email exchange this week with the Chief Operating Officer of My Plywood. He was pretty responsive until I mentioned that the bowed plywood came from a Mr Plywood store. He went very quiet then.

I hope they are replacing it!

No. I didn't request or expect that. It did amuse me, though, the way he dropped me like a hot potato when the situation became clearer.

I can deal with the bowing this time. With the next two sheets I get any distortion will be a problem. I'll warn the outlet that if the next sheet is bowed the response 'that's the nature of plywood' won't cut it and there will be tears. I always email my order so my very reasonable expectation of a flat sheet will be in writing. I'll suggest they take one from the middle of the pile for our collective benefit.