On Jun 4, 10:36 am, wrote:
Why does green treated lumber warp so much? All I can figure it's
that the treatment does something to the wood fibers that causes the
boards to deform. Standard boards rarely warp as bad.

On the other hand, I have been experimenting with these boards. Maybe
someone has already dont all of this, which is part of the reason for
this message.

I bought an 8 foot treated 2x6 and it was nearly straight. I left it
standing on end in the frame of a shed I am building. That night it
rained, and in the morning it was hot and sunny. That afternoon I
looked at that board and was shocked. It warped so much that when I
placed it on a sidewalk with the center up, the the center of the
board was a foot off the sidewalk and the ends were touching the
sidewalk.

At first I was ****ed. I just spent $8 for a piece of firewood.

....you burn treated lumber? WHY?!

But I
got to thinking that if it warped so easily and quickly, why cant I
warp it back. I placed both ends on scrap 2x4 blocks (hump side up)
and weighted the center hump with several cement blocks. Nothing much
happened at first and I even stood on it a few times. Then it rained
again, and now it's almost straight again. I still have the blocks on
it though. But someone told me that when the sun begins to beat on
it, it will warp again. We have had rain every day for the last 5
days so I may not find that out anytime soon. In the meantime I dug
out a few other treated boards and set them out in the rain and
weighted them to bend straight. One of them bent straight again, but
I took that one indoors and am letting it dry slowly. Keeping the
weights on it. So far it looks good. I have noticed that they all
curve the same direction when they do warp, so that must be the way
the grain is configured.

Thats as far as I have gotten so far, but I plan to keep trying. In
fact the local lumberyard has some really warped (cheap) treated
boards in their bargain bin, and I am tempted to buy a few to see if I
can learn more about straightening.

One thing I did find, once they are nailed in place they generally
stay straight. In fact I once used a treated 4x4 post that was so
badly twisted that the post bottom facing north, was facing east by
the time it got to the top. I used that post next to a door on a
barn, and I bolted it to the frame surrrounding it. Every day I
soaked it, then tightened the bolts a little and eventually I had a
nearly straight post. That was several years ago, and it stays
straight now that its part of the barn.

How much time and effort did that take?

Has anyone else experimented with this?

Yep. The experimentation works like this. You lose some fairly
expensive wood to warping due to not storing it correctly. You learn
not to do that again. Dimensional lumber should always be laid flat,
supported off of the ground with wood blocking every three feet or so,
and kept out of the elements (sun and rain).

Does anyone know why the treated wood warps so much?

Because it's soaked with preservative chemicals, and all dimensional
lumber deforms as it dries. Treated lumber just has a lot more drying
to do and a lot bigger potential for deformation.

R