Was looking at some plywood recently and was wondering why the different number of plys for a given thickness. It seemed to me that the sheets (3/4″ thick in this case) with the greater # of plys seemed to lay flatter. Do more, thinner plys stay straighter? Is the sheet stronger with more thin plys or fewer thick plys? I assume it is cheaper to make the sheets with fewer, thicker plys.
If I am working on a project and cost is not an issue, is it always better to use more plys? Even for a subfloor or the like? For example, I am doing a bathroom floor and it is only 8ftx9.5ft so the extra 5 or 10 bucks a sheet is no big deal if it gives me a better floor.
It seemed like the sheets rated for sheathing had fewer plys and the fancy veneered sheets had the most plys.
Just wondering.
Replies
round here all construction ply is 1/8 per ply, 1/2" 4 ply, 5/8 5 ply .. Baltic birch, cabnet grade ply has more layers, yes it is more stable, lays flatter, but why you would build a subfloor from it ???
I haven't checked too closely but I thought plywood had an odd number of plys. Maybe not.
I too used some 3 ply 1/2" junk. It would have been good for building an arch - it came pre-bent.
I think you'd have to do a search on the web or look to the forest products laboratory for your answers regarding the strength of plywood in relation to the # of plys.
I'm not so sure the number of plys has anything to do with the stability of plywood. I think it has more to do with the species. I've used plenty of Baltic birch that has been bowed or twisted and I've used many sheets of birch or maple ply with a poplar core that have been cupped or bowed also. The one species of ply I have found to be consistently flat and uniform is cabinet grade fir ply which isn't always readily available anymore.
I don't know that you can trust any of the plywoods today. Don't know if its to do with how quick they are mfg or that they aren't drying it to specs. I'm with Ted on this one. I too use a fair amount of baltic ( drawer boxes, jigs & so on ) It was always very stable but lately I've been very PO'd. The old saying of not made like it used to be is very true when it comes the plywoods today. Marine ply is the best and most consitent that I know of today, but way to pricey for subfloors.
Gary
Agree with all of that..
And as a note, i have seen more and more voids in so called "Cab Grade" ply. On a floor maybe not an issue, but man, when used for finish work and one of them voids under the superthin face veneer appears after finish is applied..kinda wrecks your day.
Even baltic birch has been getting dicey in the center plys.
IIRC the plys are MM..so a 13mm ply has 13 layers, 11 = 11 and so on.
Worst plywood I have ever seen was 1/2", 3 ply...about useless SYP. Fir was 5 ply and not a lot better.
Subfloors get Advantech here for me.
Spheramid Enterprises Architectural Woodworks
"Success is not spontaneous combustion, you have to set yourself on Fire"
Edited 3/10/2008 12:54 pm ET by Sphere
Not to start another controversy, but if I am putting in a subfloor for ceramic tile should I use advantech instead of plywood? Never used it but I understand it is some sort of "super" osb. Is that correct? Does it come in various thicknesses? How about tongue & groove? If I need to build up the floor does the advantech go on first or last?
Any other tips would be helpful.
Thanks
use it else where and not under tile..
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
So still good ol' plywood, glued and screwed is best for tile substrate ( except for ditra, but lets not go there)
I believe so...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
I prefer Advantech for subflooring. Yes its T&G and yes its plenty stiff. Ofcourse you will be using Hardie or Durock or Ditra on top too.Spheramid Enterprises Architectural Woodworks
"Success is not spontaneous combustion, you have to set yourself on Fire"
Ofcourse you will be using Hardie or Durock or Ditra on top too.
exactly.
Jeff Buck Construction
Artistry In Carpentry
Pittsburgh Pa
Make sure its rated for subfloor. You dont want any voids beneath the layers you can see.
By far and away the best plywood I've used is Finnish Baltic Birch. German and British codes (BS6655, etc)
Way better than anything except some lumber core wallnut I bought once in the 70's.
Unfortunately, what other say about decreasing quality may be true, have not been able to score any of the 13 ply BB (1 meter by 3 meters by 1.8 cm) for about 5 years, but have over a thousand sheets stockpiled.
Next house built will likely have osb (courtesy of local burg selecting ueurophobic IRC for code) to pass inspection, but all will be overlain with the BB.
junkhound
but have over a thousand sheets stockpiled.
Just shaking my head in amazement. I believe you. Just wish I had that kind of inventory or the space to store it.
Rich
'Round here, whatever you use as a subfloor needs to be rated for that use.
Advantech, Sturd-I-Floor rated plywood, OSB - all can be had with the floor rating. T&G or blocking at the long edges.
Jim
CCI
All that being said in other posts. By and large the more plys the better.
But no sense using baltic birch for a subfloor.
Rich
I have in my hand a small strip of knotty pine plywood. Eleven ply and 90.00 a sheet. I have cut it up for scraps, nailers, stickers and so on. I used about 1/3 of the sheet on a window job and the rest of it I put in shop thinking there will be something I may be able to use it for. Within two weeks the stuff is just a cut above garbage. Has more waves than the pacific. Sad.
Gary
hartlandboy
Depressing.
I remember 5 ply CDX that wa stronger and straigher than any 5/8 stuff we use now.
I love to tear out old plywood from the 50s. It's real sweet stuff.
Rich
All the Doug fir CDX I get is 5-ply....I had thought that the 4-ply experiment was a bust 20 years ago, but recently I visited a local yard that carried both 4-ply and 5-ply. (The 4-ply was a tad cheaper....but not much).
Having worked in plywood manufacture for awhile in the mid 60's and again in the early 70's, it seems counterintuitive to me that a 4-ply panel is going to have the same shear values as a 5-ply panel....or, for that matter, that any even-plied panel will have the inherent stiffness of an odd-plied panel.
That 4-ply CDX stuff is, IMO, best used for sheathing radius walls or ripped up for bender board.
I'm sorry so many of you guys are stuck with it, because, to me, a decent plywood panel beats OSB hands down.
Notchman
Most 1/2 and 5/8 CDX we get is 4 ply.
An occasional 5 ply (in 1/2) gets in by mistake.
a decent plywood panel beats OSB hands down.
I agreed. But I am seeing more delamination these days.
And OSB usually lays flatter.
Rich
I suspect gentlemen that you are going to complain even more as ply. becomes even more scarce.
frammer52
Sorry don't mean to complain.
Just don't know what to do sometimes when I go up to the pile of sheet goods.
5/8" ply is $24.33 and 5/8" OSB is $11.01.
The plywood warps even as it lays on the pile and the OSB swells on the edges when it even gets close to moisture. But hey it lays flat.
Advantech isn't a stock item around here. But now that you mention it I should check some of the other yards.
So I stand there looking at the plywood piles and wonder which should I choose.
Trying not to complain
Rich
More is better and more expensive.
Bob's next test date: 12/10/07