How to Tell If Wood Is Pressure Treated (8 Signs + Stamp Codes)
The surest way to tell if wood is pressure treated is the end tag or ink stamp: it names the preservative (ACQ, CA, or CCA), a retention in pcf, and a use category such as UC4A. Color, weight, and incision marks only hint, and gray or cracked boards prove nothing. This guide decodes the tags, ranks eight signs by reliability, and covers untagged, borate-treated, and pre-2004 arsenic-era lumber.
Read the Treated Lumber Stamp or End Tag First
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Woodlife CopperCoat Green Wood Preservative, 1 Quart – $27.35 Cutting a treated board removes the tag and exposes wood the preservative may not have reached, so the fresh end needs its own coat. The maker lists this copper-based brush-on for exactly that job.
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Lumber sold for building is supposed to carry a plastic end tag or an ink stamp, and it is the only sign that tells you what the wood was treated for, not just that it was treated. According to the American Wood Protection Association, the tag shows “AWPA U1” (the treated-wood standard), a use category, the preservative name or abbreviation, and its retention. Lumber for code-regulated construction also carries the quality mark of an accredited inspection agency, and tags name the treating company and plant.
Two real examples from a treated-wood trade group show the pattern. One Ecolife tag reads ABOVE GROUND USE, AWPA U1, EL2, 0.019 pcf, UC3B. One Copper Azole tag reads GROUND CONTACT USE, AWPA U1, CA-C, 0.15 pcf, UC4A. Notice the retention numbers: 0.019 versus 0.15 pcf. Retention is pounds of preservative per cubic foot, but it is set per preservative and use category, so a bigger number on one tag does not mean better wood than a smaller number on a different chemical.
| Tag line | What it tells you | Example |
|---|---|---|
| AWPA U1 | Treated to the primary treated-wood standard | AWPA U1 |
| Use category | Where the board may be used | UC3B (above ground), UC4A (ground contact) |
| Preservative code | Which chemical was used | CA-C, EL2, ACQ, CCA |
| Retention (pcf) | Pounds of preservative per cubic foot, compared only within the same chemical | 0.15 pcf |
| Quality mark | Third-party inspection by an accredited agency | Agency logo or checkmark |
| Treater and plant | Who treated it and where | Company name, city |
Cutting a treated board removes the tag with the end you trimmed, and it exposes wood the preservative may not have fully reached. Keep the tag from the stack, or photograph it, before you start cutting.
Treated Wood Symbols: What the Use Category Codes Mean
The use category (UC) is the line that decides whether the board belongs in your project. The AWPA lists seven categories, and most homeowner projects land on UC3B or UC4A.
| Code | Where it is meant to be used |
|---|---|
| UC1 | Interior, dry |
| UC2 | Interior, damp |
| UC3A | Exterior above ground, coated, with rapid water runoff |
| UC3B | Exterior above ground, uncoated or with poor water runoff |
| UC4A | Ground contact, general use |
| UC4B | Ground contact, heavy duty |
| UC4C | Ground contact, extreme duty |
Deck boards and railings are normally UC3B; posts set in soil need UC4A or higher. Our ground-contact chart for UC4A versus UC4B walks through which one to buy, so we will not repeat it here.
8 Signs of Pressure-Treated Wood, Ranked by Reliability
Only the first two signs and the test kit can confirm treatment on their own. The rest raise or lower the odds.
| # | Sign | What to look for | How reliable |
|---|---|---|---|
| 1 | End tag | Stapled plastic tag with preservative, retention, and UC code | Definitive |
| 2 | Ink stamp | Repeating stamp along the board with the same details | Definitive when legible |
| 3 | Incision marks | Rows of small slits, roughly 1/2 to 3/4 in. long, on every face | Strong hint; many treated boards have none |
| 4 | Tint | Green or brownish-green from copper compounds | Moderate; fades and varies |
| 5 | Weight and dampness | Heavy, damp feel when freshly treated | Weak after the board dries |
| 6 | Smell | Faintly oily, pungent odor on fresh cuts | Weak |
| 7 | Where it came from | Bin label, receipt, or project history (anything built before 2004 may be CCA) | Moderate |
| 8 | Copper test kit | Color change on damp test paper after sanding a small spot | Strong for copper-based treatments |
Incising deserves a note because it is the sign people misread. Dense species such as Douglas fir and hem-fir resist preservative, so they are cut with hundreds of tiny slits before treatment, and “INCISED” often appears on the tag. If you see those slits, the board was almost certainly treated. If you do not, it proves nothing, because many treated boards are not incised.
Why Green, Gray, or Cracked Wood Proves Nothing
Color is the first thing most people check and the least dependable. The tint comes from copper-based preservatives, but it varies by chemical and treater, and it fades as the wood weathers. Our guides on what pressure-treated wood looks like and why it comes in green, brown, or gray cover the color changes in detail. Three myths are worth correcting here.
- “Gray, cracked, or splintering wood is treated.” No. Any outdoor wood checks, splinters, and turns silver-gray under sun and rain. Weathering tells you how old a board is, not whether it was treated.
- “Cedar and redwood are pressure treated.” They are not. They resist decay naturally, which is the whole point of comparing cedar versus pressure-treated fencing. A reddish board with no tag is almost never treated.
- “A water drop test will tell you.” We could not find any standards body or manufacturer that lists a water-drop test as an identification method, so we do not recommend relying on it. A board can be treated and still soak up a drop, or be untreated and shed one.
No Tag? How to Check Old, Cut, or Reclaimed Lumber
- Inspect every face and both ends for an ink stamp, leftover staple holes from a plastic tag, or a faded stamp you can read at an angle with a flashlight.
- Look for incision marks on all faces and edges, not just the one showing.
- Trace the source. A receipt, a bin label, or a build date helps. Wood from a project built before 2004 should be assumed to be CCA until proven otherwise.
- Test for copper. One guide we read describes kits that run roughly $15 to $25 at hardware stores: you sand a small spot, collect the dust on damp test paper, and watch for a color change. Arsenic kits exist for suspected CCA wood.
- Still unsure? Treat it as treated: wear a dust mask and eye protection, do not burn it, and keep it away from food surfaces.
Plywood follows the same logic. Look for a tag or ink stamp on a face or edge, plus incision marks, because there is no long end grain to carry a tag.
Borate-Treated Lumber: Treated, but Not for Outdoor Use
Here is the angle most identification guides skip: “treated” does not always mean “outdoor-rated.” Borates are listed in AWPA use categories UC1 and UC2, which cover interior wood, and the main threat in those categories is termites. A borate-treated stud is protected for a dry or damp interior but is not meant for a deck, a fence post, or contact with soil. This is why you read the use category and not just the word “treated.”
It also changes what you do at the saw. AWPA standard M4 pairs borates with interior wood, oxine copper with exterior above-ground wood, and copper naphthenate with exterior ground-contact wood for treating field cuts and holes, so an interior borate board gets a borate touch-up, not the green brush-on pictured above.
Is It Old CCA Lumber? Safety, Burning, and Disposal
Homeowner use of CCA (arsenic) lumber was voluntarily discontinued in December 2003. Source: U.S. EPA, chromated arsenicals (CCA)
If your wood predates 2004, or the tag says CCA, treat it with extra care. The EPA does not require removal of existing CCA structures or the soil around them, but it gives clear handling advice:
- Wear goggles and a dust mask when sawing, and wash your hands after contact.
- Never burn CCA or other preservative-treated wood in a residential setting, because of possible inhalation of toxic chemicals.
- Do not use it as mulch. The EPA says homeowners may dispose of it with ordinary trash, but state and local rules vary, so call your waste authority first.
- Keeping older structures coated may reduce leaching, per the EPA.
Gloves, avoiding cutting boards or garden-bed liners made from old green lumber, and sweeping up sawdust are common-sense extras, but the EPA page above is the source for the four rules listed.
What to Do Once You Know It Is Treated
- Fasteners matter: see our picks for screws that match the coating to the exposure and deck screws for treated lumber.
- Keep it off slabs unless the code allows it: pressure-treated wood directly on concrete.
- Finishing has a waiting period: read when you can stain treated lumber and how long to wait before painting it.
Frequently Asked Questions
How can you tell if wood is pressure treated without a stamp?
Look for incision marks, a green or brownish tint, a damp or heavy feel, and a faintly oily smell on fresh cuts. None of these is proof alone. A copper test kit gives the strongest answer for modern lumber, and wood built before 2004 should be treated as possible CCA.
What do the letters and numbers on treated lumber mean?
The letters name the preservative (CA-C, EL2, ACQ, CCA). The pcf number is the retention, pounds of preservative per cubic foot. The UC code gives the use: UC3B is above ground, UC4A is ground contact. Compare retention only between boards treated with the same chemical.
Can you tell if plywood is pressure treated?
Look for a tag or ink stamp on the face or edge and for small incision marks. Treated plywood carries the same kind of preservative and use-category information as lumber. If it has no markings and no paperwork, treat it as untreated for outdoor use and do not trust it in soil.
Is it safe to burn pressure-treated wood?
No. The EPA says not to burn CCA or other preservative-treated wood in a residential setting because of possible inhalation of toxic chemicals. Take scraps and sawdust to a disposal route your local waste authority approves instead of the fire pit or wood stove.
Does treated wood always look green?
No. Tint depends on the preservative and treater, so treated lumber can look green, brownish-green, or fairly natural, and all of it fades to gray outdoors. Never rely on color alone. Read the end tag or ink stamp for the preservative and use category.
To tell if wood is pressure treated, find a tag or stamp first, use incision marks, tint, and a copper test as supporting evidence, and read the use category before you build. When you cannot tell, assume treated and handle it that way.
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