Why won't plywood lay flat anymore?

[mike_van]

Does anyone know? It's like it's all in tension or something - Big  warps, twists, interior, exterior, cdx, it all seems to do it.     >:(

[SwampDonkey]

Smaller diameter trees, juvenile wood maybe? Is it quite knotty? It will bow if stacked on it's edge to. My biggest peeve is places that store it in leaky sheds. It get water damage and ripples and separates.  >:( >:(

[Texas Ranger]

low grade wood, and sorry manufacturing.  Laid a floor using 1 1/8 tongue and grooved 4 x 8 ply wood, one in three had no glue between some plies, some had tongue and groove run out.  Price was the same.  Yard finally let us go through the stack and pick our own.

[Fla._Deadheader]

  Wuz et stomped "Hecho en Cheena", TR ???  : :

[SwampDonkey]

When I built that picnic table, we bust open a stack and sorted through it for the best. About 2/3 was what we called utility grade 20 years ago.  Might be ok for framing, but no good for aesthetics. :

An ex employee of a now defunct mill told me they used to toss the junk in the middle of the stack and put the better boards around the outside, then wrap and ship.  : :

[Texas Ranger]

Deadheader, nope, made about 70 miles from where I sleep.  SYP plywood, sorry mill.

[beenthere]

My understanding, is years ago, the better quality logs went to the plywood mills. Now, that clear, straight grain wood ends up in high-value dimension lumber that is stress graded for high-strength laminations in trusses and engineered beams. So, the plywood mills peel the lower grade, in hopes that it lays somewhat flat when glued up. Great for structural sheathing, once it is held flat with fasteners.

In the 60's, I built my house using SYP plywood that was 1/2" thick, and 5-ply.  Great if it was nailed down and covered up before it rained on it. But once wet, katy bar the door....it was on the move.