Does pressure treated lumber need to reach a proper moisture content before use?

Question

I'm planning on building a garden bench for the outdoors. I opted for Pressure treated pine (I'll be staining it a cedar color) because it was cheaper than cedar, way cheaper than white oak and mahogony, and way way cheaper than teak. I wasn't thinking when I made my decision (nor when I loaded the wood from the lumber yard), but when I brought it home, I noticed that the wood was very wet from the chemicals they used to pressure-treat it. Given what I know about moisture content, my immediate thought was that I'd have to wait a year before this lumber is ready to work with. Is this true? Will it take a year or more to get back to the proper moisture content? Or should I not even worry about it (i.e., the nature of the chemicals won't make it move)?

I know that people build with PT lumber all the time without worrying about moisture content, but these tend to be non-furniture applications.

A related question--if I can use this before it's fully dried, will regular wood-glue (e.g., Tightbond III) work? If not, will epoxy?

Thanks!

Answer 1

Pressure treated moisture is different than 'green' moisture. There is two kinds of moisture in a tree, and the stuff that takes a long time to dry is the bound moisture inside the cells.

If you sticker your lumber outside where air can flow through it, in a couple weeks the vast majority of that induced moisture should be gone and it should be ready for use.

If all you are doing is nailing or bolting things together than you don't really need to do that, other than they will be heavier to work with, and you might need to tighten things up a little when they have dried more.

Answer 2

Yes, just like any lumber, you should ideally always sticker your pressure-treated lumber and let it sit for a couple weeks before using it to let it dry out and acclimate to your environment.

Wood moves as it absorbs or releases moisture, even the moisture injected into it during the pressure-treating process. All you need to do for proof is to look at the picnic tables sitting outside your local home improvement center about halfway through the summer. After they are assembled and set outside for display, they start to acclimate and after they've been outside for a while, one leg is often several inches off the ground.

You also mentioned in a comment that you have a SawStop table saw. Typically pressure-treated lumber will not trip the brake, but there's an easy way to test whether any material is conductive enough to be detected as flesh contact.

1. Set up your saw for an extremely safe type of cut--for example, using a crosscut sled to remove a few inches of material from the end of a board
2. Start the saw in bypass mode (you should check your saw's manual, but the steps are the same as the ones I've copied below from the Contractor model's Quick Start Guide). WARNING: Only use Bypass Mode to cut conductive material or to test material conductivity. There is no protection in Bypass Mode.
   1. Flip the main power switch up to turn on power.
   2. Wait until the green light is on steady and the red light is off.
   3. Turn the bypass key clockwise and hold.
   4. Hold the bypass key turned for 2 seconds, pull out the Start/Stop Paddle, and hold the key 2 more seconds.
   5. Release the key. The green light blinks slowly and the red light is off when in Bypass Mode.
   6. Push the Start/Stop Paddle in to stop the blade. The saw exits Bypass Mode after the blade has come to a complete stop.
3. Very carefully make several test cuts.
4. Before turning off the blade by pushing in the red Start/Stop paddle, check the red light.
   • If the red light is blinking fast, the material is conductive and would have triggered the brake.
   • If the red light is off, the material is non-conductive and would not have triggered the brake.

Last summer I performed this check on a pressure-treated 2x4 and was able to safely rip a bevel across the entire length to make a piece of window trim for the exterior my house.