Within the final decade or so, thermally modified wooden—also referred to as toasted, torrified, or carmelized—has entered the market. Thermally modified wooden takes kiln-dried wooden one step additional. After being briefly air-dried, then correctly kiln-dried, the wooden is put in a particular vacuum chamber and subjected to excessive temperatures. In a traditional kiln, the air is usually heated to 140°F to 160°F. In a thermal modification chamber, the temperature is raised to between 300°F and 460°F. Earlier than the chamber is heated, a vacuum is pulled, eradicating oxygen and stopping the wooden from igniting at excessive temperatures. The therapy usually lasts from one to 2 days.
Thermal modification makes wooden rot-resistant with out making use of any chemical therapy. Wooden, like different crops, incorporates sugars and starches within the mobile make-up of its fibers. And wooden decays when mould and fungus eat the sugars and starches. Thermal modification, by advantage of the excessive stage of warmth, carmelizes the sugars and starches, modifying them right into a substance that mould and fungus can now not break down. Therefore the time period thermal modification.
One other boon for the woodworker is that the wooden’s mobile partitions are crystallized within the course of, making the wooden fibers far much less capable of take in moisture. In consequence, there’s roughly 85% much less seasonal motion in thermally modified wooden than in air-dried wooden. Modification additionally alters the colour of wooden. Relying on time and temperature within the chamber, the wooden might be turned anyplace from caramel to a deep, wealthy chocolate brown. The colour change, like the opposite advantages of the modification therapy, impacts each fiber within the wooden.
Due to its rot-resistance, thermally modified wooden is ceaselessly chosen for decking, siding, and different outside makes use of. And due to its wealthy colours and diminished seasonal motion, additionally it is seeing use in furnishings and different indoor woodwork.
This course of could also be comparatively new to the market on a industrial scale, but it surely isn’t a brand new concept. Vikings have been hearth charring the hulls of ships tons of of years in the past to stop barnacles from rising and inflicting rot. Native People used hearth to harden and treatment arrows and different instruments. And Japanese woodworkers have lengthy been scorching wooden to protect it.
One draw back of thermally modified wooden is that the heating course of makes it extra brittle. The wooden fibers develop into extra inflexible and lots much less prepared to bend as in comparison with kiln-dried wooden, and much more so in comparison with air-dried wooden. Additionally, as thermal modification crystallizes the wooden’s cell partitions, they develop into much less capable of take in moisture. If you’re coating thermally modified wooden, use an oil-based primer, and keep away from use of any waterborne finishes, as a result of they won’t bond correctly.
Moreover, when gluing thermally modified wooden, it is suggested that you simply enhance the clamp time over kiln-dried wooden, significantly with water-based glues.
-Jeffrey Schucker cuts, dries, mills, and sells wooden at Bailey Wooden Merchandise in Kempton, Pa.
What about torrefied wooden?
Today, luthiers and musicians generally hear the phrase “torrefied” when discussing the wooden used to make guitars and mandolins. As this web site is for and by woodworkers, you could be blissfully unaware of the obsession (affliction?) that many musicians endure from—continuously chasing that “classic” tone. For years now, I’ve heard torrefied wooden being utilized in my guitar-related wanderings. The speculation is that thermally modifying the wooden replicates the getting older means of instrument tonewood.
After a number of looking, I really feel assured saying that there’s little to no distinction between “thermally modified” wooden and “torrefied” wooden. Each thermally modifying wooden and torrefying wooden are outlined as the method of subjecting wooden to excessive temperatures in an oxygen-depleted surroundings.
The top purpose might not at all times be the identical although—torrefied is generally in regards to the “tone” of the wooden with the colour being little greater than a facet impact. The very fact of the matter is that the luthiery neighborhood has leaned into utilizing the phrase ‘torrefied’—which I think is as a result of it sounds lots fancier!
The video above dives into a few of the traits of torrefied wooden that luthier Don Macrostie argues provides his devices the played-in tone he’s going after. Whereas I don’t advocate leaking nitrogen into any a part of your store, Don’s experimentation could be very fascinating!
-Ben Strano
Other ways to dry wooden
Horizon Sawmill Tour: Kiln Drying
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