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Should I expect Plywood To Be Flat ?

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GAJ52

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I ordered two sheets of 8 x 4 Poplar 18mm Plywood from my local builders Merchant to make some cabinets for my workshop. Not having bought plywood for some time I just let the delivery driver unload them and he drove off. When I carried them to my workshop I noticed they were slightly bowed and not flat is this acceptable ?

Glen
 

That would work

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Put them flat on a flat surface and they probably would be.
It sounds like you've bought shuttering ply so I wouldn't expect too much of it in that respect. I would think though by the time you cut it up and do what you are intending it will be absolutely fine.
 

D_W

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GAJ52":20b08qpu said:
I ordered two sheets of 8 x 4 Poplar 18mm Plywood from my local builders Merchant to make some cabinets for my workshop. Not having bought plywood for some time I just let the delivery driver unload them and he drove off. When I carried them to my workshop I noticed they were slightly bowed and not flat is this acceptable ?

Glen
it is standard fare for building supply places around here to provide birch or luan ply that doesn't stay flat. I don't know where it's used (in walls, on floors? I don't know - not a builder).

about five years ago, I bought ply from a local shop that sells only to commercial customers. It was a grade on both sides, cherry and flat. I built my kitchen with it (hand planed the sides on the last cabinet just for fun - no problem, plenty flat). Last year, I built another cabinet to go with the kitchen and used the last of the ply - it's still flat.

Good ply stays flat - this stayed standing on edge in an unheated garage and still no change in flatness.

But, as stated above - if i special ordered birch plywood from home depot here, I wouldn't expect it to be flat. I'd feel lucky if one of the two sheets was flat.
 

worn thumbs

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Define flat?You can get some very curly 6mm ply from some sources.A mild bend in 18mm shouldn't be a disaster but it may take a bit of pulling flat.If its laid flat and no part is more than an inch or so off the ground you can normally work with it.I wouldn't advise leaving it too long as storage conditions may affect even the modest amount of bend.
 

GAJ52

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One sheet is worse than the other, if I lay it down on a flat floor the middle section is raised by about 25 - 30mm, if I push it down it springs up again.

Could that curve come out if I put a weight on it.
 

AES

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IME, the answer to the OP's Q is "Well, it depends".

An awful lot depends on A) the material used, and B) the number of plies.

By that I mean that if a really soft wood is used, and there are only 3 or 5 plies, then I doubt if it was really flat even within 5 minutes of leaving the mill (exaggeration for illustration effect).

OTOH, if the ply is made of a hard wood and has at least, say, 7 or 9 plies, it's likely to stay flat throughout its life provided you store it sensibly (without any obvious possibilities for it to warp).

For example, the desk tops in my office are all 11 plies, some sort of hardwood (don't know what, can't really see it, covered both sides with some sort of "Formica") and are 19 mm thick. That stuff isn't going anywhere, and the design is such that it isn't really "held" by the structure.

Agree with a poster above, it sounds like the OP has bought shuttering ply or something and that is unlikely to be flat or stay flat. How many plies does it have?

I can understand buying cheap if it's "only" for cupboards, etc, in the workshop, but IMO, multi strand board ("OSB") would have been a better buy (pretty ugly but can be painted up OK).
 

GAJ52

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Many thanks guy's for the continued response to my question. As I said in my opening post I haven't bought plywood for some time so don't know the quality supplied by builders merchants etc.

Just to clarify its definitely not shuttering ply, its a hard wood of some sort as each face resembles a light coloured hardwood not pine and it has eleven layers, I was told this was furniture grade plywood and called Poplar Ply and made in China.

If we wasn't going through this Coronavirus problem I would have gone back to the builders merchant to bring it to their attention, but do to my lack of experience with this product I will just except it as a lesson learned.
 

AES

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OK, I'm definitely NOT an expert, but as you've described the ply I would say it should NOT be bent/warped.

So under "normal conditions" I would send/take it back, but with Corona, who knows??? I would suggest though that IF you can wait until "things return to normal" then OK, send/take it back.

If not, and if you know the supplier well/have an account with them, then it MAY be worth taking some pix and talking to them after things are normal, the object being to get some sort of "rebate" (money, goods, credit note).

Assuming you do want/need to use it before "normal" times are back I can only suggest that you follow several of the tips from previous posters and try and rig up some weights (e.g. water in bucket/s) so that you can get it back to "flat" (but IME, "flat" is more likely to end up as "flat-ish", in which case you may have to modify you design so that your structure tries to compensate).

HTH, good luck.

AES
 
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