Thermal Modification Is Coming: Why Knot Thermally Modify Knot-Free Wood?
I used to be heavily involved with thermally modified wood (TMW). For those unfamiliar, thermal modification is the process of heating lumber to at least 350°F in an oxygen-depleted environment to prevent combustion. This heat treatment crystallizes (or “cooks”) the hemicellulose, the sugar in the wood, reducing the wood’s ability to absorb moisture. The result is increased dimensional stability (about 50 percent less shrinking and swelling) and enhanced durability, comparable to naturally durable species.
If the temperature is raised to around 410°F, the wood becomes even more durable but loses some mechanical and structural strength. Push the temperature too far, and you’re left with a lump of charcoal—rot-resistant, yes, but unsuitable for nails or construction. While that extreme is mainly used for research, TMW is an excellent product for outdoor applications like decking, siding, fencing, and indoor uses such as flooring, cabinetry, furniture, windows, and doors.
To be fully transparent, I’m biased toward this technology because I’ve believed in its potential for a long time. My interest in thermal modification began in 2002, when I was an undergraduate in Wood Products Processing at the University of British Columbia. I traveled to Ligna in Hanover, Germany, to meet with equipment manufacturers and learn their unique processes for controlling oxygen in TMW systems. I later worked as the Technical Director of SMI International, a marketing firm studying the North American TMW market. I represented Jartek, a TMW equipment supplier, in North America, helping to sell a research system in Quebec and a complete commercial system in Minnesota.
Jartek also supported my master’s degree research, where I focused on TMW as a value-added commodity to help rural communities become more sustainable. I eventually purchased my own small TMW system and operated it in British Columbia until 2012.
Like many early adopters, I was ahead of the market, but the time for thermal modification has come. Now more than ever, the industry must come together to support new rules and standards to help grow and stabilize thermally modified hardwood markets.
One lesson from the early days: we cannot afford to overpromise and underdeliver. Even with thermal modification, it’s still wood. It will still check, fade, and behave according to the quality of the material going in. Knotty, waney wood doesn’t improve in appearance after modification; it just becomes more stable and durable. TMW can add value to underutilized species, but it is not a silver bullet for low-grade lumber. And remember, the market we’re competing with isn’t knotty pressure-treated pine, it’s clear, tropical hardwoods.
NHLA is now leading the effort to form a thermal modification association. Interestingly, this brings things full circle for me. When I worked for Jartek 15 years ago, I joined NHLA. I collaborated with John Hester and others to promote thermal modification, published articles in Hardwood Matters, and exhibited at conventions in Vancouver and Nashville.
Let me be clear: this isn’t about a personal comeback but an industry opportunity. Thermal modification represents low-hanging fruit that is already commercially viable. Many North American hardwood species are being thermally modified in Europe, and then shipped back to the U.S. I’ve personally modified more than 50 different species, including Red Oak, White Oak, Hickory, Maple, Birch, Ash, Poplar, and others. My office is still full of samples. When I interviewed for my current role at NHLA, I brought a 10-inch-wide, 8/4 thermally modified White Oak plank into the room. It sparked a conversation that’s still going.
There are a lot of myths and misconceptions about TMW. If you’ve heard claims that it lasts forever or that specific applications aren’t possible, you were misinformed. It won’t last forever but can work with the proper process and inputs. It’s simply a matter of choosing the right species and determining whether the application justifies the cost.
If you’re interested in thermal modification, reach out to the NHLA. Let’s talk. We’re moving forward with this and want to do it right, building standards and certifications that ensure consistent quality, no matter who’s producing it. Whether you’re working with softwoods or hardwoods, NHLA is here to help the industry deliver what the market demands.
Thermal Modification is coming. Why Knot thermally modify knot-free wood?
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