You've seen them stacked behind the hardware store. Practically speaking, maybe you've even bought a few for a garden bed or a retaining wall. They're heavy, dark, and they smell like something your grandfather's garage — sharp, oily, unmistakable.
But here's the thing most people don't ask: what exactly* is in that wood?
What Are Railroad Ties Soaked In
The short answer: creosote. But that's like saying a cocktail is "soaked in alcohol." Technically true. Missing the whole story.
Creosote isn't one chemical. Phenols. In practice, the exact mix varies by batch, by refinery, by the source coal. Polycyclic aromatic hydrocarbons (PAHs). Cresols. It's a distillation byproduct — usually from coal tar, sometimes from wood tar — and it contains hundreds of distinct compounds. Because of that, naphthalene. What ends up in the tie depends on where the treating plant bought its creosote that month.
And creosote isn't the only game in town.
The Big Three Treatments
Coal-tar creosote — the industry standard for over a century. Cheap, effective, toxic as hell. It's what you're smelling when you walk past a tie pile in July heat. The EPA classifies it as a probable human carcinogen. The EU banned it for consumer use in 2003. In the U.S., it's restricted to commercial applications — railroads, utility poles, marine pilings. You can still buy used ties at the garden center. That's a regulatory gap, not a safety endorsement.
Pentachlorophenol (penta) — an oil-borne preservative that took off mid-century. Less smoky than creosote, but it comes with its own baggage: dioxin contamination during manufacture. The EPA restricted it to heavy-duty uses in the 80s. Most new ties don't use it anymore, but millions of penta-treated ties are still in track.
Copper naphthenate — the "greener" alternative gaining traction. Copper-based, lower toxicity profile, doesn't leach as aggressively. Railroads have been slow to switch — it's pricier and some old-timers swear it doesn't hold up as well in high-decay zones. But Class I roads are testing it. You'll see more of it in the next decade.
What About Newer Stuff?
Borates. ACQ (alkaline copper quaternary). Think about it: copper azole. These show up in residential lumber — deck boards, fence posts, sill plates. They're water-borne, cleaner to handle, and they don't* work for railroad ties. The treatment doesn't penetrate deep enough. Ties need 2.5 to 3 inches of saturation minimum. Water-borne preservatives can't get there in Douglas fir or oak without incising the wood (those little slash marks you see on treated deck boards), and incising weakens a tie that already takes a beating.
So the industry stays with oil-borne. Practically speaking, creosote. In practice, penta. That's why copper naphthenate. That's the menu.
Why It Matters / Why People Care
You're not a railroad engineer. Why does this matter to you?
Because those ties show up in your* world.
The Garden Bed Problem
This is the big one. They're cheap ($15–25 used), they last forever, they look rustic. That said, people love railroad ties for raised beds. And they leach creosote into your soil.
How much? Fruit crops? Root vegetables — carrots, potatoes, beets — are the worst offenders for uptake. A 5-year-old tie in wet acidic clay? Depends on age, temperature, soil moisture, pH. Studies have found PAHs migrating 6–12 inches from tie walls into adjacent soil. Minimal. Leafy greens less so. Now, a 30-year-old tie in dry alkaline soil? In practice, significant. Almost none.
But "almost none" isn't zero.
And here's what nobody tells you: the creosote doesn't stay in the wood forever. It volatilizes. Day to day, on a hot day, you're breathing naphthalene and phenol vapors. That said, that "railroad tie smell" is the chemical leaving the wood. Every year, the tie gets a little less toxic — and your soil gets a little more.
The Playground Issue
Old ties as playground borders. On top of that, retaining walls near sandboxes. Kids sit on them. Touch them. Put hands in mouths. The EPA says don't use creosote-treated wood where frequent skin contact happens. That includes playgrounds. Yet you'll see them at schools, parks, daycares — installed 20 years ago by well-meaning volunteers who didn't know.
Indoor Use? Just Don't.
I've seen ties used as mantle beams. Coffee table bases. Bed frames. One guy built a headboard from three ties and wondered why his bedroom smelled like a telephone pole in August.
Creosote off-gasses indoors. No UV, no rain, no soil microbes to break it down. Long-term exposure to creosote vapors is linked to respiratory irritation, skin sensitization, and — per the EPA — increased cancer risk. Consider this: the vapors accumulate. Not "maybe." The agency's IRIS assessment is clear.
If you have creosote-treated wood inside your house, get it out. Seal it if you must keep it (epoxy, multiple coats, every surface), but honestly? Replace it.
How It Works (or How to Do It)
Let's talk about the treating process itself. Because understanding how the chemical gets in explains why it's so hard to get out.
The Pressure Treatment Cycle
Fresh-cut ties (green wood, 40–60% moisture content) don't treat well. The cell lumens are already full of water. So step one: seasoning. Air-dried or kiln-dried to 20–30% MC. Takes months air-drying. Days in a kiln.
Then the retort — a horizontal steel cylinder, 150 feet long, rated for 200+ psi.
Initial vacuum — 22–26 inches Hg. Pulls air from the wood cells. Critical step. Skip this, and you get "refusal" — wood won't take chemical.
Flood — creosote heated to 190–210°F fills the cylinder. Hot creosote penetrates better. Lower viscosity. Also drives residual moisture out of the wood as steam.
Pressure period — 150–200 psi held for 2–6 hours depending on species, size, target retention. Southern pine takes creosote easy. White oak fights you. Douglas fir is somewhere in between.
Final vacuum — pulls excess creosote back out. Recovers chemical. Reduces surface bleed.
Steam conditioning (optional) — some plants hit the charge with steam to expand the oil in the wood, drive it deeper, then vacuum again.
Want to learn more? We recommend are wax melts bad for you and acs award for team innovation 2018 recipients affiliated institutions for further reading.
Target retention for mainline ties: 8–12 pounds per cubic foot (pcf) of creosote. Because of that, that's pounds of chemical per cubic foot of wood*. A standard 7×9×8.5 tie is about 3.1 cubic feet. At 10 pcf, that's 31 pounds of creosote in one tie*.
Thirty-one pounds. In a piece of wood you can almost lift.
Species Matters
Southern yellow pine — the workhorse. Treats beautifully. High permeability. Most ties in the Southeast and Midwest.
Douglas fir — standard in the West. Harder to treat. Often incised (those parallel knife cuts) to meet penetration specs. Incising helps chemical get in but creates stress risers. Ties split faster.
White oak / red oak — dense, refractory. Hates taking creosote. Used to be common in the Northeast. Now rare. Most "oak ties" you see for sale are actually mixed hardwoods — hickory, gum, map
— hickory, gum, maple — that treat marginally better but still nothing like pine.
Incising deserves a closer look. Those parallel knife cuts — 1/2 inch deep, 3/8 inch apart, four faces — aren't decorative. They're mechanical forced penetration. Without them, Douglas fir heartwood treats to maybe 1/4 inch. With incising, you get 1/2 to 3/4 inch in the sapwood, maybe an inch in the heartwood if the kiln schedule was right. But every incision is a crack starter. Check any old incised tie: splits radiate from the knife marks. The treatment that saves the wood from rot helps destroy it mechanically.
The Penetration Problem
Here's what the spec sheet doesn't tell you: retention is an average. Penetration is the reality.
AREMA (American Railway Engineering and Maintenance-of-Way Association) specs require 85% sapwood penetration or 1/2 inch minimum, whichever is greater. Heartwood? No requirement. It's considered untreatable.
So a tie tests at 10 pcf average. That's not a failure. The outer inch is saturated — 20, 30 pcf. Near zero. Which means the core? That's the standard.
Why it matters: when that tie sits in ballast, the saturated shell leaches creosote into the groundwater. The dry core rots from the inside out. You get a hollow cylinder of preserved wood holding up a rail. Eventually the shell crushes or splits, and the tie fails — often with 60% of its original creosote still locked in the outer fibers.
Disposal: The Expensive End
Railroads pull 15–20 million ties a year. Used to be they gave them away. In practice, farmers used them for fence posts, retaining walls, barn foundations. Landscapers loved them. "Free rustic timber.
EPA put a stop to that. In real terms, creosote-treated wood is now a listed hazardous waste (F034) if it comes from a wood-preserving process. Still, a tie weighs 200 pounds. Must dispose of it at a Subtitle C hazardous waste landfill — $150–300 per ton. Practically speaking, railroads can't give it away. Can't sell it. Do the math.
Some plants burn it in permitted boilers with emission controls. Energy recovery. But the ash is still hazardous. And public opposition to "burning toxic railroad ties" is fierce.
The black market persists. In real terms, you'll still see stacks of "landscape ties" at flea markets, farm auctions, Craigslist. No paperwork. Consider this: no warnings. Just weathered wood smelling like a telephone pole on a hot day. Which means buying them makes you the generator of hazardous waste. Practically speaking, legally. Financially.
Alternatives: What Replaces It?
Borates — water-soluble, low toxicity, great for interior use. Useless in ground contact. Rain washes them out in months.
Copper naphthenate — the current industrial favorite for ground contact. Green-brown, oil-based, penetrates well. Less toxic than creosote by orders of magnitude. But it leaches copper into soil — toxic to aquatic invertebrates. And it's expensive: 3–4x creosote cost.
Polymer-modified creosote — creosote cut with heavy petroleum oils, sometimes polymer additives. Reduces volatility, improves handling. Still creosote. Still carcinogen. Just... slower to off-gas.
Concrete ties — 650 pounds each. No treatment needed. Last 50+ years. But they don't flex. Ballast degrades faster. Rail fatigue increases. And the carbon footprint of cement? Massive. Railroads use them on high-tonnage mainlines. Secondary lines stay wood.
Composite/plastic ties — recycled HDPE, fiberglass reinforced. Impervious to rot, insects, chemicals. Lighter than concrete, heavier than wood. Cost 3–5x wood. Long-term creep behavior still being proven. Promising for switches, crossings, curves where wood fails fast.
Thermally modified wood — heated to 400°F+ in oxygen-free kilns. Sugars caramelize, hemicellulose degrades. Fungi can't eat it. No chemicals. But strength drops 20–30%. Brittle. Not rated for mainline track. Yet.
The Bottom Line
Creosote is a 19th-century solution that worked too well to die. It turns biodegradable wood into a 40-year structural element for pennies per board foot. The chemistry is brutal, the handling is nasty, the disposal is a nightmare — but the economics still pencil out for Class 1 railroads moving 100 million gross tons a year over 140,000 miles of track.
For you? The homeowner? The woodworker? The landscaper?
**There is no safe way to use creosote
railroad ties. The health risks—linked to cancer, reproductive issues, and chronic respiratory problems—are well-documented. Even if you never burn them, bury them, or let them touch your skin, the chemicals will eventually leach into the soil, air, and water. And while the alternatives exist, they come with trade-offs: higher costs, shorter lifespans, or environmental footprints of their own.
The truth is, railroads will keep using creosote as long as it delivers unmatched durability and low upfront cost. But public pressure, stricter regulations, and innovation in sustainable materials are slowly shifting the needle. Composite ties are gaining traction in niche applications, and thermally modified wood is being tested for lighter-duty tracks. Yet a full transition will take decades—if it happens at all.
For now, the message is clear: If you value your health, your community’s safety, and the planet’s future, steer clear of creosote-treated wood. Choose alternatives that may cost more today but won’t haunt tomorrow. And if you spot those old, weathered ties at a flea market, admire them from afar. They’re not just relics of a bygone era—they’re a warning.
