What is Pressure Treated Wood?
What is pressure treated wood? Well, the conversation went something like this:
Kenny: “Wow, that’s actually pretty impressive… the DeWalt just drilled a 3″ hole in pressure treated wood on high speed with no real trouble at all.”
Me: “…wait…what is pressure treated wood exactly?”
Kenny: “Hey, that’s a great idea for an article!”
So, here we are. You’re reading this because I had to go shooting off at the mouth. See, this is what happens when I ask questions around here – Kenny knows that other people have the same one so my teachable moment becomes everyone’s teachable moment.
I kid, though. I was actually curious about this topic, and figure maybe there are scores of others who’ve never bothered to learn this fun tidbit until now. So, I’ll take one for the team and do a bit of research. If you did the right thing and Googled the same question that I asked, you might be here reading this, rather than writing an article about it. So, hat’s off if that’s you.
Anyway, the million dollar question: what is pressure treated wood?
What is Pressure Treated Wood?
Classic pressure treated lumber makes use of CCA – chromated copper arsenate. That’s chemistry-speak for chromium, copper, and arsenic. Sounds like something you really want to spend time swinging on, huh?
In late 2003, the EPA made some changes to keep your kids’ playset and your front porch swing a little less toxic. However, the entire reason we use pressure treated lumber is to make what we build last longer and that desire remains unchanged. However, CCA still remains in play for non-residential
Enter stage left ACQ (alkaline copper quat) as the most popular alternative. CC (ammoniacal copper citrate), ACC (acid copper chromate), and CA-B (copper azole) are other names that can pop up. It doesn’t take long to see the trend – arsenic is out and copper is key pressure treating lumber. Copper helps prevent breakdown by an assortment of insects and fungi. The downside is that copper readily releases into the soil and environment around it.
The process remains the same – lumber enters into a chamber or tank, filled with the chosen chemical agent, and then the tank is pressurized, promoting absorption into the wood. That pressurized stage is where the process “pressure treatment” gets its name. Adding pressure to the mix forces the chemical treatment deeper into the wood than it could go with simple soaking.
Wood can air dry in most cases, though some moves to the kiln to bake it in. When the wood requires the extra step of kiln drying, the price goes up accordingly.
How Much Chemical is Actually in the Wood?
Considering the chemicals used in pressure treated wood don’t do us any favors if we ingest it (hence why you don’t burn PT or breathe in the sawdust when cutting it), you might find it interesting to know that there are between 0.40 and 0.60 pounds of chemical per cubic foot of wood, depending on the application.
So there you have it. The next time someone asks “what is pressure treated wood?” you’ll be the smartest guy in the room. And then your friends, impressed by the depth of your knowledge, will have no choice but to buy you a drink out of sheer awe.
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