Those who have spent some time working with wood know that the building material comes in different types, and they’re not all equally suited for every project. Other than the features that depend on the type of tree the wood came from (i.e. maple, oak, birch, etc.), how wood is used also comes down to whether or not it’s pressure treated.
If you’re buying new lumber, you’ll know this based on its label (and if not, ask someone who works at the retailer). But if you come into some wood another way—and don’t have a lot of experience working with it—you may not know how to tell whether it has been pressure-treated.
Fortunately, there are a few different ways to figure it out, and Wade Shaddy, a building expert specializing in hardwood furniture, walks us through several of them in an article for Hunker. Here’s what to know, and why it matters.
What is pressure-treated wood?
According to the Oklahoma State University Extension, the process of pressure-treating wood involves forcing “preservative chemical deep into the cellular structure of the wood.” The chemical then prevents the wood from deteriorating as a result of moisture, insects (like termites), and fungi, in order to extend the life of the wood.
So what kind of chemicals are we talking about? Up until 2003, chromated copper arsenic (CCA) was the preservative of choice. But as it turns out, arsenic isn’t great for humans or the environment, so the lumber industry and the Environmental Protection Agency (EPA) came to the agreement that CCA-treated wood wouldn’t be used in most residential construction moving forward.
How to tell if wood has been pressure treated
In most cases, figuring out whether wood has been pressure treated is pretty straightforward, Shaddy says. Older pressure-treated wood has an olive-green tint, while newer pressure-treated wood has a stamp identifying it as such, and, in some cases, an alphanumeric code providing information on the level of toxicity.
If the stamp has “Borate,” “Tim-Bor,” or “Hi-Bor” printed on it, then it has been treated with borate, which provides protection similar to CCAs, but is generally safe to use indoors or outdoors, Shaddy explains. Sometimes, instead of stamping the wood, manufacturers add a greenish patina to indicate that it has been treated with borate. According to Shaddy, “it’s a brighter color than the old-school green tint used on CCA lumber.”
Finally, Shaddy says that when it doubt, sniff it out:
If all else fails, smell it. Natural wood has an outdoorsy, pleasant smell. Pressure-treated wood has an oily scent. If it doesn’t smell oily, other chemicals may impart a disagreeable odor to the wood. Another indicator is small, 1/2- to 3/4-inch incisions at regular intervals on all four sides.
Why does it matter?
In short, it’s important to know whether lumber has been pressure-treated to ensure you’re using the best type of wood for a specific job, and also for safety purposes. According to HomeAdvisor: “Wood for any outdoor project should be pressure-treated; wood for indoor projects should be left as is. The sawdust from pressure-treated wood is an irritant to the eyes, skin, and nose.”
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