I bought six sheets of birch ply, let it sit in my garage for a couple of
weeks, then eventually cut it down into strips roughtly 12x94.

a week later, I got around to working with those strips and found a number
of them to be warped to the tune of about 1/4 to 1/2 inch, maybe even a
little more.

I'm wondering if this is normal behavior? I thought that plywood was supposed
to be dimensionally stable and not prone to warping.

one thing I did note in this stuff is that, a couple of the cuts show that
the plywood has irregular plys, ie, they're not all straight if you look down
the edge of a cut side. thereare places where one ply had a void, and the
next ply seemed to sink down a bit to fill it. the exterior still seems
flat and stable, but I'd never seen this sort of thing before...

any comments appreciated.

....myoung

Seen the same sort of ply structure when purchased from the big boxes (Lowes, HD). Their supplier has a ineffective QC
department. Of course these were about $40 per sheet whereas the local hardware store was charging $60 per sheet. I got
what I paid for. ;-(

JAW


myoung wrote:
I bought six sheets of birch ply, let it sit in my garage for a couple of
weeks, then eventually cut it down into strips roughtly 12x94.

a week later, I got around to working with those strips and found a number
of them to be warped to the tune of about 1/4 to 1/2 inch, maybe even a
little more.

I'm wondering if this is normal behavior? I thought that plywood was supposed
to be dimensionally stable and not prone to warping.

one thing I did note in this stuff is that, a couple of the cuts show that
the plywood has irregular plys, ie, they're not all straight if you look down
the edge of a cut side. thereare places where one ply had a void, and the
next ply seemed to sink down a bit to fill it. the exterior still seems
flat and stable, but I'd never seen this sort of thing before...

any comments appreciated.

...myoung

Naturally I don't know what happened with the plywood once you took it home
but I have to opine that..............................

Plywood is essentially stable however that doesn't mean it can be left
leaning against a wall or in any other way improperly stored, supported or
in a less then ideal environment and not take a set from it's own weight.
That holds triply true once you have made small relatively narrow strips of
it and rob it of a lot of it's internal strengths. We are not talking steel
I beams here.

--
Mike G.

Heirloom Woods
www.heirloom-woods.net
"myoung" wrote in message
om...
I bought six sheets of birch ply, let it sit in my garage for a couple of
weeks, then eventually cut it down into strips roughtly 12x94.

a week later, I got around to working with those strips and found a number
of them to be warped to the tune of about 1/4 to 1/2 inch, maybe even a
little more.

I'm wondering if this is normal behavior? I thought that plywood was
supposed
to be dimensionally stable and not prone to warping.

one thing I did note in this stuff is that, a couple of the cuts show that
the plywood has irregular plys, ie, they're not all straight if you look
down
the edge of a cut side. thereare places where one ply had a void, and the
next ply seemed to sink down a bit to fill it. the exterior still seems
flat and stable, but I'd never seen this sort of thing before...

any comments appreciated.

...myoung

Depends on two things:

(a) How the store you bought it from treated it.
(b) How you stored it after you bought it.

Standing plywood up against a wall(most people do it)
will result in a warped/bowed sheet.

It was probably warped/bowed a wee bit when you bought it.

I suspect you are talking about bowing, not warping. As you
stated, plywood is stable, but it's wood and it will move
and sag/bow when stored.



myoung wrote:

I bought six sheets of birch ply, let it sit in my garage for a couple of
weeks, then eventually cut it down into strips roughtly 12x94.

a week later, I got around to working with those strips and found a number
of them to be warped to the tune of about 1/4 to 1/2 inch, maybe even a
little more.

I'm wondering if this is normal behavior? I thought that plywood was supposed
to be dimensionally stable and not prone to warping.

one thing I did note in this stuff is that, a couple of the cuts show that
the plywood has irregular plys, ie, they're not all straight if you look down
the edge of a cut side. thereare places where one ply had a void, and the
next ply seemed to sink down a bit to fill it. the exterior still seems
flat and stable, but I'd never seen this sort of thing before...

any comments appreciated.

...myoung

myoung wrote:
I'm wondering if this is normal behavior?

Yes.

I thought that plywood was supposed
to be dimensionally stable and not prone to warping.

It is fairly dimensionally stable in the X and Y axis but
not in the Z.

UA100

"myoung" wrote in message
om...
I bought six sheets of birch ply, let it sit in my garage for a couple of
weeks, then eventually cut it down into strips roughtly 12x94.


How did you get 94 inches out of a sheet? Did you cut diagonally?

a week later, I got around to working with those strips and found a number
of them to be warped to the tune of about 1/4 to 1/2 inch, maybe even a
little more.

I'm wondering if this is normal behavior? I thought that plywood was
supposed
to be dimensionally stable and not prone to warping.

I have not seen any plywood that will not warp to some extent. Plywood is
dimensionally stable in that its length and width does not change.
Thickness will change with temperature and humidity. Irregular thickness
changes cause the plywood to warp. For best results, DO NOT LAY plywood on
a concrete floor when storing and do not store it on edge.


one thing I did note in this stuff is that, a couple of the cuts show that
the plywood has irregular plys, ie, they're not all straight if you look
down
the edge of a cut side. thereare places where one ply had a void, and the
next ply seemed to sink down a bit to fill it. the exterior still seems
flat and stable, but I'd never seen this sort of thing before...

This is commom.

"Leon" wrote in message
.. .

PLEASE disregard the following ignorant questions.... I musta been thinking
....who knows what I was thinking.



How did you get 94 inches out of a sheet? Did you cut diagonally?

"Leon" wrote in message
. ..

"Leon" wrote in message
.. .

PLEASE disregard the following ignorant questions.... I musta been
thinking
...who knows what I was thinking.



How did you get 94 inches out of a sheet? Did you cut diagonally?



Hey, at least we got a chuckle out of it. Maybe is was the Baltic birch 5 x
5 stuff.

BTW, I'm going to sell some tape measures on eBay, but I'll offering them
here first. They measure a full 92" or eight feet, whichever comes first.
Ed

Just to follow up on the thread...

the plywood was layed out in full sheets on a set of 2x4s on my garage floor
for about three weeks. one of the sheets "bowed" a little (thanks for the
clarification). the other sheets looked ok. I cut them down into 12" strips
and layed them out again for a couple of weeks (much to the dismay of my
girlfriend, who's waiting for the end product). when I got back to them,
I noticed the bowing in a number of them.

to address another observation, I guess I too got what I paid for...the
couple of sample sheets I saw looked like they had more plys than the 70$
sheets, and had two good sides of veneer, while the $70 stuff had one clear
white birch side, and a second side with a little more color. I paid about
43$ a sheet... sigh...

live and learn. shame too...since I sort of liked buying from the smaller
place...

....myoung

myoung wrote:

Just to follow up on the thread...

the plywood was layed out in full sheets on a set of 2x4s on my garage floor
for about three weeks. one of the sheets "bowed" a little (thanks for the
clarification). the other sheets looked ok. I cut them down into 12" strips
and layed them out again for a couple of weeks (much to the dismay of my
girlfriend, who's waiting for the end product). when I got back to them,
I noticed the bowing in a number of them.

I'd say that moisture evaporating from the ground through the garage floor was
absorbed by the face of the plywood facing the floor. This caused that side of
the plywood to expand causing the bow.

--
Jack Novak
Buffalo, NY - USA
(Remove "SPAM" from email address to reply)

The latest issue of "Fine Homebuilding" magazine has a brief article
about how to unbow plywood. Using a spray bottle of water, wet down
one side of the plywood, then place it on your driveway in the sun.
Unfortunately, I don't remember which side you're supposed to spray or
which side goes face down (the wet side, I'm pretty sure). I do
remember you need to monitor it closely or it'll bow the other way.

You could either buy the mag or experiment with one piece. If the
wood is unusable as is, you;ve got nothing to lose.

On 28 May 2004 07:15:16 -0700, (dpsours) wrote:

The latest issue of "Fine Homebuilding" magazine has a brief article
about how to unbow plywood. Using a spray bottle of water, wet down
one side of the plywood, then place it on your driveway in the sun.
Unfortunately, I don't remember which side you're supposed to spray or
which side goes face down (the wet side, I'm pretty sure). I do
remember you need to monitor it closely or it'll bow the other way.

You could either buy the mag or experiment with one piece. If the
wood is unusable as is, you;ve got nothing to lose.

My father straightened cupped or twisted doors with this method,
except he placed the door on the grass in the sun for 3-6 hours. The
side you wet goes against the grass, placed in the sun. The side you
wet will expand and swell--that will clue in on how the board will
bend. I've used this method and it works (surprisingly) well.

Nova wrote in message ...
I'd say that moisture evaporating from the ground through the garage floor was
absorbed by the face of the plywood facing the floor. This caused that side of
the plywood to expand causing the bow.

seems unlikely...the weather here is pretty dry...and it probably would
have only affected the lower must sheet...no?

myoung wrote:

Nova wrote in message ...
I'd say that moisture evaporating from the ground through the garage floor was
absorbed by the face of the plywood facing the floor. This caused that side of
the plywood to expand causing the bow.

seems unlikely...the weather here is pretty dry...and it probably would
have only affected the lower must sheet...no?

Survival training teaches you can trap water by collecting moisture evaporating from the
ground even in desert sand.

--
Jack Novak
Buffalo, NY - USA
(Remove "SPAM" from email address to reply)