How to tell if wood is treated

How to Tell If Wood Is Treated? (And Why it Is Important)

From Nadya: This is a post from my hubby Brett. I persuaded him to write about his latest experience about pressure-treated wood and how to tell if wood is treated. Enjoy!
A couple days ago my neighbor gave me some nice, rustic-looking pieces of wood. He had torn up the small deck and steps at the back of his house, and had no use for the old lumber. 

My first thought was to create some great shelves for the kitchen and toss the rest into our fire pit out back.

Then Nadya reminded me that you can't burn pressure-treated wood, and that it's not safe to be used as shelves or furniture either. Since I couldn't remember how to tell if wood is treated, I did some research— and I decided to share my findings with all of you.

Understand the Purpose of Treating Wood

When I'm referring to treated wood, I'm talking about a specific kind of chemical pressure treatment. Why do manufacturers subject wood to pressure treatment in the first place? Usually, it's to prevent unwanted deterioration due to fungus, termites, or rot.

During the pressure treatment process, the wood soaks in chemical preservatives, then moves to a large chamber with an airtight door. That vacuum chamber creates powerful pressure that forcibly inserts additional chemicals into the wood fibers themselves.

Once the lumber is pressure-treated, it can last for decades, sometimes up to 40 years. Because of this, cities often use this treated wood for utility poles, docks, or bridges. If you're building a garage, a shed, a tree house, or a deck, that longevity can be a useful quality. However, in some cases, you need to know that your lumber is clean and free of chemicals.

Know Your Softwoods

Before you learn how to tell if lumber is pressure treated, you need to be familiar with softwood versus hardwood lumber. Most pressure-treated wood is softwood lumber, which comes from coniferous trees like Douglas fir, white pine, yellow pine, and spruce.

Lumber from softwood trees is naturally wetter, since these trees have much more sap than hardwoods do.  Due to the extra sap, it makes sense that the softwoods would require pressure treatment to increase their longevity. Plus, the natural pathways for the sap ensure that the pressure-treatment chemicals find their way deeper into the wood.

If you know that the lumber you're looking at is hardwood, it's unlikely that is has been pressure-treated.

Look for an End Tag

Check the piece of lumber for a stamp or label that designates it as pressure-treated wood. An end tag like this should have the name of the preservative used on the wood, as well as the rating, preservation company, and other related information.

You'll want to avoid using any wood that was treated with Chromated Copper Arsenate (CCA). This preservative includes a form of arsenic and increases the risk of cancer. CCA-treated wood is now prohibited for use in decks, playgrounds, and similar structures in an outdoor-residential setting.

Find the Stamp

Builders still employ CCA-treated wood for industrial use and for structural supports. If the wood you're looking at was treated after the 2003 prohibition of CCA, it most likely contains the chemical alkaline copper quaternary (ACQ) instead.

Look for a stamp somewhere on the wood. A stamp that reads "L P22" indicates wood treated with arsenic, which is the least safe variety. This type of wood can withstand direct contact with the earth— think of a structural support or fence post. Lumber stamped as "L P2" isn't quite as toxic, but still isn't safe for building a playset or home furniture.

One of the safest types of pressure-treated wood often bears the stamp "FDN" for foundation. Builders sometimes use it as the base underneath home flooring.

Lumber that has been pressure-treated with borate is also safe for internal use in homes and causes no harm to humans. To identify borate-treated lumber, look for the stamp "Bor," "Hi Bor," or "Tim Bor."

Check the Color

If there is no end tag, you may wonder how to tell if lumber is treated. You'll have to look more carefully for clues, including a faint olive-green hue to the wood. If the wood is too weathered to distinguish any color but gray, carefully cut into a portion of the lumber at an angle. You can also check in the grooves or joints for any green tint that would indicate CCA pressure treatment.

How to Tell If Wood Is Treated: Know Your Lumber: CCA-treated wood

You can distinguish borate-treated wood by its blue color. Builders often use this type of lumber in homes, to defend against termites. While it is considered a low-toxicity lumber and safe for humans, it is not intended for exposed use in outdoor areas. Not only can it rot, but its chemicals may leach into the soil.

How to Tell If Wood Is Treated: Know Your Lumber: borate treated wood

Do the Smell Test

Suppose you don't see any stamp or end tag, and you can't identify any specific blue or green tint? At that point, I just pick up the chunk of wood and take a deep sniff. If it's untreated wood, it should have a nice, fresh, natural smell— a kind of outdoorsy fragrance. Some kinds of pressure-treated wood have an oily or chemical smell.

However, the most dangerous type of treated lumber, CCA lumber, has no distinguishable odor. If you suspect that the wood may be older than the year 2003, use my last tip for how to tell if lumber is pressure treated.

Use a Swipe Test Kit or Wood Testing Kit

The Healthy Building Network and many commercial labs can provide you with a swipe test to determine, once and for all, if the wood you are examining has been pressure-treated. Once you obtain your wood-testing kit, follow the included instructions to check your lumber's status. At that point, you'll know if you can use it in a project or if you need to safely get rid of it.

Follow Safety Recommendations

If you suspect that some lumber you have may be pressure-treated, educate yourself about proper handling and disposal.

Careful Handling

When you pick up the wood, wear gloves, at the very least. The government also recommends extra measures like a dust mask and goggles if you're sawing or sanding the wood. Make sure that you clean up any scraps or sawdust, and take a shower after working with the wood.

Correct Disposal (video)

Check this YouTube video for tips about removing pressure-treated wood safely:

If you have some treated lumber that you'd like to dispose of, don't burn it! That is illegal in every state due to the toxic chemicals released during the burning process. You can contact your local landfill to find out if they are approved to accept the treated wood, and they will let you know about approved disposal methods and regulations.

What About My Wood?

Unfortunately, the wood my neighbor gave me wasn't as natural and clean as it looked. I discovered that it was pressure-treated with CCA. So, I took a quick trip to my local landfill, where they accepted the wood and disposed of it correctly. I'm also planning to order a a wood-testing kit to make the process easier if I come across more would like this.

Now that you know how to tell if wood is treated, you can do a quick check to see if your old lumber is safe. If you have some additional tips for confirming if wood is natural or treated, share them in the comments section!


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