How to Tell If Wood Has Been Pressure Treated and Why It Matters

Those who have worked with wood for a while know that building materials come in different types, and not all of them are the same for every project. Besides the characteristics that depend on the type of wood from which the wood was sourced (eg maple, oak, birch, etc.), how the wood is used also depends on whether it is pressure treated.

If you buy new lumber, you will know from the label (or if not, ask someone who works in the store). But if you hit some wood in a different way – and you don’t have much experience with it – you may not know how to tell if it has been pressure treated.

Fortunately, there are several different ways to figure this out, and Wade Shaddy, a construction expert who specializes in wood furniture, walks us through a few of them in an article for Hunker . Here’s what you need to know and why it matters.

What is pressure treated wood?

According to the Oklahoma State University expansion , the wood pressure treatment process involves injecting a “chemical preservative deep into the cellular structure of the wood.” The chemical then prevents damage to the wood from moisture, insects (such as termites) and fungi to prolong the life of the wood.

So what kind of chemicals are we talking about? Until 2003, chromium-plated copper arsenic (CMC) was the preservative of choice. But, as it turns out, arsenic is harmful to humans or the environment, which is why the forest industry and the Environmental Protection Agency (EPA) have agreed that CCA-treated wood will not be used in most residential buildings.

How to determine if wood has been pressure treated

In most cases, figuring out if wood has been pressure treated is fairly straightforward, Shaddy said . Old pressure treated wood has an olive green hue, while new pressure treated wood has a stamp that identifies it as such and, in some cases, an alphanumeric code that provides information on the toxicity level.

If the stamp is printed with Borat, Tim-Bor, or Khai-Bor, then it has been treated with borate, which provides similar protection to CCA, but is generally safe for indoor or outdoor use. explains Shaddy . Sometimes, instead of stamping wood, manufacturers add a greenish patina to indicate that it has been treated with borate. According to Shaddy, “This is a brighter color than the old-school green shade used for CCA wood.”

Finally, Shaddy says if in doubt, sniff:

If all else fails, smell it. Natural wood has a pleasant street smell. Pressure treated wood has an oily odor. If it does not smell like oil, other chemicals can give the wood an unpleasant odor. Another indicator is small 1/2 to 3/4 inch notches at regular intervals on all four sides.

Why does it matter?

In short, it is important to know if the lumber has been pressure cut to make sure you are using the best wood grade for the job and also for safety reasons. According to HomeAdvisor : “Wood for any outdoor project must be pressure processed; wood for interior projects should be left as is. Sawdust from pressure treated wood irritates eyes, skin and nose. “


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