Sax-Zim welcome center sided with 'thermally modified' aspen

Saw boards out of aspen and stick them on the outside of a house in northern Minnesota and you probably wouldn't have much in a few years. The stuff would rot and fade and likely not make it through many of our extreme seasons -- from cold and dr...

"Thermally modified" aspen
Volunteer Ben Yokel, who was staffing the new Sax-Zim Bog Welcome Center near Meadowlands on Sunday afternoon, describes the special kiln-dried process used by the NRRI to make the wood used on the outside walls of the center more weather-resistant. (Bob King /

Saw boards out of aspen and stick them on the outside of a house in northern Minnesota and you probably wouldn't have much in a few years.

The stuff would rot and fade and likely not make it through many of our extreme seasons -- from cold and dry to hot and humid.

But if you "cook" those aspen boards at just the right temperature for just the right time, they can be has hardy as any cedar siding on the market, says Pat Donahue, director of the Market-Oriented Wood Technology Program at the Natural Resources Research Institute at the University of Minnesota Duluth.

That's why 1,200 board feet of the NRRI's "thermally modified" aspen siding is now covering the exterior of the new welcome center built by the Friends of the Sax-Zim Bog near Meadowlands, to serve birders visiting the area.

It's the first public test site for the NRRI material.


"It's a little like baking cookies. You can have an oven and have the dough, but if you don't have the right recipe, you don't end up with much. What we are doing is developing just the right recipes for Minnesota species ... so we can get back some added value, some jobs, instead of having to import all the wood we use for siding and windows and doors,'' Donahue told the News Tribune.

Demand for some Minnesota wood products, from paper to waferboard, has declined in recent years, spurring plant closures and resulting in the loss of hundreds of jobs related to logging and processing. Meanwhile, Minnesota species such as aspen, ash, birch and even red pine have been spurned for years as poor quality for most lumber-related products. But Donahue says it doesn't have to be that way -- that thermally modified wood could help bring some of those jobs back.

Take Minnesota's huge window manufacturing companies, for example. They use millions of board feet of lumber every year. But nearly all the wood they use is pine imported from western states and overseas, from as far away as New Zealand, Donahue said.

"If that wood could come from Minnesota, if we can provide a better product that's cheaper with local trees," he said, leaving the idea hanging for a moment. "We might not see any giant new manufacturing plant develop, but we'd see a lot more jobs for our loggers and our sawmills and our local communities that have really taken a hit in recent years."

The idea of thermally modified wood isn't new. Companies in Finland, Germany and Denmark have been doing it since the 1990s; the "oven" the NRRI is using comes from Denmark.

The process also allows the use of bountiful tree species while avoiding more sensitive species such as cedar or rain-forest trees.

"I think it's really going to take hold. The architects are starting to use it as part of sustainable forestry efforts to get away from the exotic woods,'' said John Bieganek, owner of Superior Thermowood Inc. in Palisade, one of about a dozen U.S. companies trying to wade into the thermally modified wood business

Bieganek owns his own thermal modification "oven'' to cook basswood, oak and ash. He's even sent thermally modified wood to the Fender guitar company to be made into custom guitars.


"People like to use native trees; it's part of the green movement," he said. "Right now, most of our business is in California where they don't want to use Brazilian hardwoods or western redwoods."

Bieganek, who has three employees now, also has "cooked'' aspen to be used in sauna siding.

"We've sent thousands of samples out to people and we're finally starting to get people calling back,'' he said. "We've done plywood and OSB and laminated beams now. ... If we can make those rot resistant, and so it doesn't expand, that's a game changer for the construction industry."

In addition to the Sax-Zim Bog welcome center test site for siding, several companies are contracting with NRRI to test thermally modified wood for their products, ranging from siding to doors to outdoor decking to windows and more. Donahue said companies are very interested in the fact that thermally modified wood becomes completely water resistant; the chemical and physical characteristics of the wood are altered so it no longer absorbs any atmospheric moisture.

That makes the wood more stable than any of its competitors.

"It may not sound very sexy, but if we could just make the best double-hung side jamb in the industry, and I think we can, that would be huge for our area,'' Donahue said. "We're now importing hundreds of truckloads of wood from out of state to make those."

Thermal modification may even be used to salvage ash trees that succumb to the expanding emerald ash borer.

NRRI wood researcher Matt Aro recently landed a $600,000 grant from the National Science Foundation to find out how thermal modification affects engineered wood products -- the kind made out of glued-together pieces. Eventually, such products could be used instead of waferboard, or OSB-type products, and thermal modification could cash in on a U.S. housing construction market that's finally expanding after years of lethargy.


"If we can take local red pine for 30 cents per board foot and treat for another 20 cents, that would still be half the cost of imported cedar at $1 a board foot,'' Donahue said. "It makes sense on paper. The concept is right. The product works. We just need to get it out there."

John Myers reports on the outdoors, natural resources and the environment for the Duluth News Tribune. You can reach him at
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