How To Tell If Wood Is Pressure Treated

Pressure treated wood is used for many outdoor and indoor projects. It has been treated to resist insects, mildew, mold, and fungal rot to help extend the natural lifespan of the wood. It’s important to know how to tell if wood is pressure treated so you select the type of lumber best suited for your project.

Pressure treated lumber is often a different color and has a different smell than untreated wood. It is also heavier, slightly wider and thicker, and may feel damp or furry compared to similar untreated wood. Additionally, the lumber stamp, tag, and fact sheet will identify the type of preservative used in the treatment.

In this guide, we’ll explain the difference between treated and untreated wood and how to tell if the wood has been treated. We’ll also discuss how to tell if old wood was pressure treated too. Our aim is to help you determine if wood has been pressure treated so you get the best material for your indoor or outdoor project.

Treated vs Untreated Wood: What’s the Difference?

Treated wood has been infused or sealed with a clear or uniform green, brown, black, or tan color protective chemical coating to prevent insect, mold, mildew, and fungal rot or damage. It may also be colored pink with a fire retardant or blue with a waterproofing agent.

Wood is treated so that it will last longer under the conditions it is treated for than untreated wood would. Untreated wood can also be treated after purchase, but the treatment usually doesn’t penetrate as deeply, so isn’t as effective.

Untreated wood is often of the same dimensions and species as treated lumber but hasn’t been factory treated with protective chemicals. It is often lighter, drier, and less expensive since it hasn’t been pre-treated by a supplier and will also have a natural wood color and smell.

Untreated lumber is often used for interior purposes or where it is protected from the elements. It will fade or gray if exposed to the elements for prolonged periods. Plus, since it’s untreated, it is susceptible to moisture, mold, mildew, rot, and insect damage. If it will be used above or below ground for exterior projects, it needs to be treated with an appropriate protective agent.

Newly treated wood is easy to differentiate and usually has end tags and/or lumber stamps identifying the type of treatment and potential use locations. Even though it is often kiln-dried, it may be wetter and heavier than untreated wood of the same dimensions and species or have a metallic-type smell and/or incised marks. Treated lumber that has been exposed to the elements will often weather and fade in color if a protective sealer or coating isn’t reapplied every 12 to 36 months.

How to Know if Wood Is Treated

Wood is treated to protect it from specific conditions. Wood at a lumber yard is often fresh from a manufacturer, so should be easier to identify. The Table below identifies and explains six ways to tell if the wood has been treated.

How To Tell If Wood Is Pressure Treated

Wood is pressure treated to protect it from insects, mold, mildew, and fungal rot. It is typically used for exterior projects or interior applications that may be exposed to moisture or insect concerns. There are different chemicals like copper, arsenic, and creosote used in the treatment that can leach out over time and may prove harmful to children or if consumed.

Knowing if wood has been treated is important so it can be used appropriately. Treated wood goes through additional processes than untreated wood, so the first way to tell is often the cost; treated wood it’s more expensive. Below are eight other ways to determine if wood has been treated.

Color

The chemicals used to treat wood often give it a more uniform color. Pressure treated wood may have a greenish, brownish, tan, or even black coloring instead of the natural wood tone of untreated wood. The color typically identifies the chemical and that the wood has been treated.

A green color is from chromated copper arsenate, brown from copper azole, and amine (ammonia) copper-quat (ACQ) is tan or olive in color. Creosote is used to preserve railway ties and looks black or dark brown. Pentachlorophenol can make wood light brown to dark green and copper naphthenate turns wood light to dark brown, both preservatives are commonly used for utility poles.

A darker or more solid coloring often indicates that the wood has been infused with a greater concentration of chemicals, which may identify its use location. Less chemical absorption usually means above-ground use, more concentration means near or touching the ground, and darker has the greatest for underground or better protection.

Unfortunately, color can fade over time, plus borate preservatives are clear and don’t change the color of treated wood. So, color may not be the best indicator.

Lumber Stamp

Lumber may have a stamp somewhere along its length and/or a tag stapled or glued to an end. Both identify the type of preservative (aka chemicals) used to treat the wood, plus whether it is for interior, exterior, above, near/on, underground, or marine grade use.

The stamp also has the wood species, grade, moisture content, mill, and certification mark. The following is a list of preservatives including their abbreviations and coloring.

• acid copper chromate (ACC) – green
• alkaline copper quaternary (ACQ) – tan or olive
• micronized copper quaternary (MCQ) – light greenish-brown
• chromated copper arsenate (CCA) – greenish tint
• copper HDO – green coloring
• copper azole (CA) – brown
• copper naphthenate – light to dark brown
• creosote – black or dark brown
• pentachlorophenol (PCP) – light brown to dark green
• sodium borate (SBX) – natural wood color

Smell

The ‘sniff’ test is another way to identify if wood has been pressure treated. Water-based preservatives will often have a chemical or plasticky smell while oil-based preservatives usually have an oily smell. Since most pressure treated lumber is pine, spruce, or fir which has a nice fragrance, lumber that smells off, plasticky, oily, or of chemicals is probably treated.

Incisions

Wood or lumber with 1/2″ to 3/4″ long cuts or incisions regularly spaced over the entire surface have been incised. The cuts allow the preservatives to penetrate deeper into the wood for greater protection. Incisions may be used on all species, but are typically used for harder woods like Douglas fir and oak.

Weight

Pressure treated lumber tends to retain both chemicals and moisture from the treatment process. As a result, individual boards will be heavier than untreated lumber of the same dimensions.

However, much depends on the moisture content of the lumber being compared, but if the moisture content and dimensions are the same, the treated wood will weigh more. For example, an untreated eight-foot 2×6 with 19% moisture content will weigh between 12 and 16 lbs, while a pressure treated one will be between 22 and 30 lbs.

Size

Pressure treated lumber is commonly made of milled dimensional lumber that has been kiln or air-dried to less than 20% moisture content. So, it starts out being the same dimensions as untreated dimensional lumber. However, the pressure treatment forces the liquid-borne chemicals into the wood, which makes it swells.

The result is that the lumber is slightly thicker and wider than untreated lumber of the same original dimensions. Even when it dries to the same moisture content as an untreated piece, it will still be slightly larger.

Information Sheet

The EPA and other safety organizations require products that contain chemicals to have information sheets. The sheets identify the types of chemicals contained and any risks they pose, safety precautions, storage, best uses, and disposal.

Hardware, home improvement stores, lumber yards, and anywhere else that retail pressure treated lumber is required to have the fact sheets on hand and available upon request. So, asking for an information sheet is a sure way of finding out if the wood is treated or not.

Wood Test Kit

Wood test kits are available to check if treated wood contains arsenic. CCA (chromated copper arsenate) was phased out of residential use by 2004. Unfortunately, resale or recycled lumber may be old enough to contain arsenic, or it may be new lumber from an industrial site or slated for industrial use where it is still acceptable.

Check your local lumber suppliers or online to purchase or order a test kit. Follow the instructions provided with the kit, which usually includes testing some sawdust from the wood. The results will identify the level of arsenic in the wood. Unfortunately, it won’t otherwise identify if the lumber has been pressure treated if there’s no arsenic.

How to Tell if Old Wood Is Treated

Newly pressure treated wood is fairly easy to identify. It is typically heavier, wetter, has an unnatural color and smell, feels ‘furrier’, and is slightly wider and thicker than untreated lumber of the same dimensions. However, wood that has been exposed to the elements for a month or more may be hard to tell. Also, if the wood came from a second-hand lumber yard, was free, a yard sale purchase, or is recycled wood, it can be more difficult to tell.

A test kit only identifies if the wood was treated with CCA. If the results show no arsenic, that doesn’t mean the wood is untreated. If the wood has incised marks, it’s been treated. The stamp or tag may no longer exist or be visible, so that doesn’t help.

Old fence or deck boards and lumber used for outdoor structures weather over time and may even have been stained or painted. Weathering, paint, and stain can make it near impossible to tell if the wood was originally treated.

Treated wood that has only been weathered, painted, or stained on one or two surfaces will still retain much of its original color on the protected surfaces. So, if one or more faces have a greenish or brownish tint, it is probably treated lumber.

Another way of identifying if old wood was treated is to do a cross-cut. The exposed wood will often show a greenish or brownish ring of color 1/4” to 1/2″ thick around the perimeter of the cut if it is treated. Unfortunately, if treated with sodium borate (SBX) that won’t help.

Old untreated wood will typically be gray and may show insect or moisture damage. It may be slimy and even black with age or have fungal growth on it. A crosscut will also show white or yellowish coloring and no pressure treatment ring around the perimeter.

If the wood is cedar, cypress, redwood, or another naturally resistant species, the sawdust from a crosscut will often give off the natural wood scent. The cut will also reveal a uniform color and no treatment ring.

Pro Note: Provided the wood doesn’t contain arsenic or lead from paint, it should be acceptable for use on interior or exterior projects whether treated or untreated.