Pressure-treated wood is a commonly used building material for a variety of projects including both residential and commercial projects.
But when you’re buying lumber, how do you know if it’s treated lumber or regular wood?
In this post, I’ll explore how to tell if wood is pressure treated, the different types of pressure treated lumber, and much more. Let’s dig in!
In This Article:
What Does Pressure Treated Lumber Mean?
For wood to become “pressure-treated”, it must go through a multi-step process that involves heavy machinery and high-tech computers.
Essentially, special preservatives are forced into the wood by way of pressure, and these preservatives strengthen the wood and make it long-lasting.
Afterward, pressure-treated wood usually goes through another process so it’s flame-retardant.
Nowadays, pressure-treated wood is used to construct a variety of structures, which in part explains why there are different kinds of pressure-treated wood.
While in theory every kind of pressure-treated wood can be used for a project that calls for it, some kinds are better for some projects whereas other kinds are ideal in different scenarios.
Because of its strength and lifespan, pressure treated lumber is usually more expensive than its natural wood counterparts.
Ways to Tell if Wood Is Pressure-Treated
There are several ways to tell if wood has been pressure-treated or not. Usually, all that’s required is checking the informative tag or stamp which details what the wood has been treated with. But if there’s no tag or stamp present, you’ll have to resort to a different strategy, and these strategies are detailed below.
Pressure-treated wood can have a range of tints, and the kind of tint a wood has depends on the preservatives it’s loaded with.
For example, when softwood (pine, fir, spruce, etc.) is pressure-treated, it is turned dark brown by the chemicals.
Even if a piece of wood has the color that pressure-treated wood usually has, it’s best to run another test, like smelling the wood, to confirm that it is in fact pressure-treated.
As wood gets older, it tends to discolor, and you could mistake an old, unsound piece of wood for something pressure-treated if you’re going off color alone.
Pressure-treated wood also has a distinct smell.
Specifically, it smells like chemicals, which makes sense since the wood is treated with a variety of chemicals to make it stronger. Even water-based preservatives have a distinct smell, albeit slight. Oil-based preservatives, on the other hand, will give off an oily smell, and this wood may be slick.
Regardless of what wood has been treated with, the sure thing is that it’s not going to have that natural wood smell after it’s been treated with chemicals. So if you have spruce or pine board—both of which are naturally fragrant—and you don’t smell anything but chemicals, it’s almost certain the wood has been pressure-treated.
Pressure treated lumber will weigh more than non treated wood because of all the chemical components added during the treating process.
By comparing one piece of lumber to another – you should be able to spot which one has been treated because it will weigh significantly more.
Pressure-treated lumber is usually larger than natural lumber because the addition of preservatives makes pressure-treated wood swell; it’ll become less swollen over time as it dries. The size difference is slight, but it’s enough that you shouldn’t ignore this phenomena when designing a structure that requires pressure-treated wood.
If wood has been pressure-treated recently, and therefore it’s still wet, you should refrain from painting on it, as it’s likely the paint won’t set and instead peel or chip off later because it didn’t adhere properly.
You should also give the wood adequate time to dry before building with it, as if it’s still swollen during construction, it’ll shrink later on and possibly affect the shape, size, or soundness of the structure.
Some woods require incisions in order to become pressure-treated.
The incisions can be anywhere from a 1/2 inch to 2 inches in length, and usually there are dozens of incisions in regular intervals. Hardwoods usually require these incisions because the preservatives won’t penetrate and remain in the wood without them.
One thing to keep in mind about incisions is that they don’t automatically indicate wood has been pressure-treated. An old piece of wood, for example, may have similar incisions because someone attempted to work with it before.
After wood has been pressure-treated, it’s tagged or stamped with a list that includes all the chemicals used to treat the wood.
A tag or stamp can be located anywhere on the wood, but usually manufacturers put either near the end of a board.
Not only does the tag/stamp list the preservatives used to treat the wood, it also briefly explains how the preservatives were applied. Here’s a list of preservatives that are commonly used to treat wood:
- Acid copper chromate (ACC)
- Alkaline copper quaternary (ACQ)
- Copper azole (CA)
- Pentachlorophenol (PCP)
- Sodium Borate (SBX)
- Micronized Copper Quaternary (MCQ)
You can also purchase a test kit to determine whether or not wood has been pressure-treated.
That said, a test kit won’t reveal what exactly has been used to treat the wood, unless chromated copper arsenate (CCA), a form of arsenic, is detected. Up until 2004, this chemical was used widely by manufacturers to pressure-treat wood, but after the dangers of using it came to light, it was phased out and substituted with chemicals that are not nearly as harmful yet still effective.
Testing a piece of wood for chemicals will not damage the wood. In fact, the test kit runs on sample saw dust, so you won’t have to alter the board in any way to test it.
If CCA is detected in the board, which confirms the wood has been pressure-treated, it’s better to use a safer wood for building, no matter what the project is.
If you’re getting pressure-treated wood from a big box hardware store or lumber mill, you should be able to get a consumer information sheet with your purchase.
This sheet will provide more detail than the tag/stamp discussed earlier, and the Environmental Protection Agency (EPA) requires that manufacturers produce these sheets so consumers know which chemicals were used to treat the wood and how treating was conducted.
If you’re unsure of whether or not a piece of wood has been pressure-treated, the consumer information sheet will provide a clear answer. And this sheet doesn’t just detail what chemicals were used and how they were applied—it also indicates how flame-retardant the wood is and how the wood should be cut and handled.
What Types of Pressure-Treated Wood Are There?
There are two main types of pressure-treated wood: above-ground pressure-treated wood and ground-contact pressure-treated wood.
Above-Ground Pressure-Treated Wood
Maintaining above-ground pressure-treated wood is easy, and replacing it is a breeze too.
If a structure is more than 6 inches off the ground, above-ground pressure-treated would can be used.
And in order for this wood to stay in good condition for a long time, there needs to be proper ventilation as well as an efficient drainage system around the wood.
Ground-Contact Pressure-Treated Wood
Ground-contact pressure-treated wood is used to construct structures that are less than six inches from the ground.
It’s stronger than above-ground pressure-treated wood, in large part because it’s loaded with more chemicals.
In areas where there’s poor ventilation and little to no drainage system, ground-contact pressure-treated wood should be used, as it doesn’t require much maintenance and you shouldn’t have to replace it often.
As far as grade is concerned, the less blemishes a piece of wood has, the higher its grade will be. And with a higher grade comes a higher price.
If a board is low-grade, it’s more prone to splitting, cracking, and warping.
Pros and Cons of Using Pressure-Treated Lumber
Like any other material, there are pros and cons associated with using pressure-treated lumber. But since pressure-treated wood is required in many localities, it’s fair to say the pros associated with using it far outweigh the cons. That said, it’s still important to understand the cons listed below, as these may make pressure-treated wood the wrong material for your project.
Pressure-treated wood’s durability is the main quality that makes it sought-after across the industry.
It can resist dents and scratches far better than untreated wood, and it takes a very long time for this wood to be worn down by natural elements.
It’s also stronger, so it can support more weight.
Because of its unmatched durability, pressure-treated wood is used for both commercial and residential buildings and projects.
In many instances where natural hardwood would not be sufficient, pressure-treated does well—think decks, docks, porches, sheds, etc. It’s even more durable if you stain pressure treated wood.
While using pressure-treated wood in its natural state is certainly possible, usually this wood is stained or painted. And because it can display an innumerable amount of colors, it’s more versatile than other materials, namely stone and vinyl.
Just make sure you stick to using interior wood inside and exterior wood outside, as exterior hardwood looks odd indoors while interior hardwood won’t hold up long against the elements.
Pressure-treated wood is affordable in two ways.
First, certain kinds of pressure-treated wood are cheaper than many natural hardwoods, including cedar and redwood.
Second, since you don’t have to replace pressure-treated wood often, it delivers a much higher return on investment (ROI).
That being said, when you compare many kinds of pressure-treated wood to their natural wood counterparts, you’ll find that pressure-treated woods are generally more expensive, but the difference isn’t all that much in most cases.
In the end, if you’re determining value based on how long the wood will last, pressure-treated wood is far more affordable than natural wood (which may have to be replaced often).
Ease of Repair
Not only are instances that result in pressure-treated wood repair rare, it’s both easy and inexpensive to repair or replace pressure-treated wood.
Say, for example, you drop a burning coal on your deck while grilling and it chars the wood—it’ll be easy to replace that part of the board with a piece that looks the same and fits perfectly.
Although “natural” isn’t the first word you might associate with a piece of wood that’s loaded with chemicals, it is natural in the sense that it looks and feels like natural wood, especially if it’s been painted or stained to remove the chemical tint.
Therefore, if you want the look and feel of natural wood with added strength and protection, choosing pressure-treated wood is a no-brainer.
What Color Is Pressure-Treated Wood?
The color of pressurized wood is in large part determined by the preservatives used to treat it. Commonly used chemicals are chromated arsenicals (CCA), copper azole, alkaline copper quaternary (ACQ), and borate.
CCA turns wood green. Therefore, if you find a piece of pressure-treated wood that has a green tint, stay clear—this wood could be dangerous if it’s loaded with CCA.
Copper azole will turn a piece of wood light drown, and this chemical is considered a safer alternative to CCA. Wood that’s been treated with this chemical will become silvery-gray over time.
Alkaline Copper Quaternary
Wood that’s been treated with ACQ will turn tan or olive, and it’ll stay this color unless it’s painted or stained. The olive color ACQ produces doesn’t look anything like the color CCA turns wood, so you don’t have to worry about confusing the two. ACQ is relatively safe, and there are four kinds of ACQ pressure-treated wood: A, B, C, D.
Borate is used when other preservatives aren’t able to penetrate a hardwood. Borate diffuses once it’s penetrated the wood, whereas other chemicals would bond to the wood fibers. It’s a preferred material in residential foundation construction because it’s non-toxic and it doesn’t change the wood’s color.
Oil-based preservatives will either darken or lighten the wood. Specifically, creosote will turn it dark brown, pentachlorophenol will turn it light brown, and copper naphthenate can turn it dark green. The color wood retains after treatment is also in part determined by how much of each preservative was used.
How to Tell if Wood Is Treated for Burning
Like pressure-treated wood, flame-retardant wood is supposed to be properly labeled so the consumer knows how strong it is, what chemicals were used to treat it, etc.
The tag or stamp that provides these details should be near one of the ends of the board.
When reading a label, one metric you should look out for is “Flame Spread“. This number indicates how combustible wood is on a scale from 0 to 100.
According to the International Building Code, pressure-treated wood must have a Class-A flame spread rating, i.e. a rating below 25.
The amount of smoke created when the wood burns is also measured by a 0-100 scale, where a lower rating means the wood doesn’t emit as much smoke when burned.
When flame-retardant wood is installed, the tag which details its qualities should be visible so inspectors and code officials can easily access it.
What Is the Difference Between Pressure-Treated and Untreated Lumber?
Pressure-treated wood is different from natural wood in several key ways.
First, pressure-treated wood is stronger than natural wood, as it’s loaded with preservatives that make it wear-resistant, sturdier, dent- and scratch-resistant, and weather-resistant.
Pressure treated wood is also more flame-retardant than natural wood because of the chemicals it’s loaded with.
The appearances are different as well.
Natural wood looks the most like, well, real wood, whereas pressure-treated wood sometimes can’t hide the fact that it’s been treated with chemicals. But pressure-treated wood is more versatile than natural wood, as it has far more applications in both the commercial and residential building industries.
Final Thoughts on How to Tell if Wood Is Pressure Treated
There are several ways to tell if lumber is pressure treated or not. Looking at the color, smell, size, incisions, and the end tag are all easy ways to determine if lumber has been treated.
The tag is the easiest way to spot pressure treatment, but looking at the color and weight of the wood can also be key indicators.