Fixing Warped Green Treated Lumber

[george90810]

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 pissed. I just spent $8 for a piece of firewood. 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.

Has anyone else experimented with this? Does anyone know why the treated wood warps so much?

George

[dpb]

...

There was another thread on this just last week and it's surely one of the most oft-discussed subjects.

It isn't the treatment chemicals that does something to the wood as much as it is simply that it is wet and isn't dried as is "regular" construction lumber. It's the unconstrained and uncontrolled drying that causes the lumber to "move" for the most part. If you had untreated lumber of the same species and similar grain and growth characteristics, if it were simply water-soaked and left to dry on its own, it would warp and twist essentially the same way.

As for your "experiments", the water initially leaves the board in an uneven fashion (closest surface/end first) and sunlight exacerbates the problem. Wetting it replaces the water and tends to return it to it's previous position. Fixing it firmly in place to hold it while it dries is usually pretty effective and is how most is intended to be used.

One can, for a price and with diligence in finding it, purchase kiln- dried PT lumber that will, if protected from the elements after drying, be much more stable...

[RicodJour]

...you burn treated lumber? WHY?!

How much time and effort did that take?

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).

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

[dpb]

...

Not a disagreement, but some amplification (and not really so much for you Rico as for reinforcement for OP)...

It's not nearly as much to do w/ the chemicals per se as it is simply the water bearing the chemicals required to perform the treatment.

ALL lumber (dimensional or not) is subject to warp/bow as it dries. The amount and general susceptibility is dependent on the particular piece of wood (growth characteristics, sawing, etc.) within general trends of the wood species itself.

It is correct that treated lumber as received is generally far wetter than standard construction-grade lumber and so the drying process is more of an issue. As noted in previous post, while not commonly found, kiln-dried PT lumber is available (for a price, of course)...