While all of the other treatment options involve adding chemicals to the wood, a new preserved-wood product, which will be shipped starting in March 2008, relies instead on heat and steam. The product, PureWood, is manufactured by Bay Tree Technologies using a sophisticated thermal-modification process.
Along with protecting the wood from decay and insect attack, the thermal-modification process makes the wood more stable. The process reduces shrinking and swelling by 80%, according to the maker. These chemical changes also dramatically reduce checking. Thermally modified wood has been used in Europe since the mid-1990s and is commonly used there for decking, outdoor furniture, highway barriers, and saunas.
The samples show that the wood is significantly darkened, like a hardwood, even though the grain pattern still looks like southern yellow pine. (The wood also has a pleasant toasted aroma, which diminishes over time.) The traditional decking boards (called Sahara by Bay Tree Technologies) are 1¼" (32 mm) thick by 5" (127 mm) wide. The company also produces a European-style decking (Linea) with narrow ribbing on one side and wider ribbing on the reverse; its dimensions are identical to those of Sahara. Both products are produced in two-foot increments from 8' (2.4 m) to 20' (6 m). The Linea line’s ribbing offers a more comfortable feel underfoot and provides a unique appearance (see photo).
After the thermal-modification process, all of the boards go through a high-speed molder that produces the finished dimensions and the ribbed profile on the Linea product. All PureWood boards are suitable for outdoor aboveground and ground- contact applications and carry a 25-year warranty—even in ground-contact. The product can be painted, stained, and sanded just like conventional wood. Because there are no chemicals in the wood, scrap can be burned (depending on local regulations) without creating hazardous air pollution or toxic ash.
PureWood is fairly expensive, similar in price to the “tropical” composite products, such as Trex Brasilia and TimberTech Earthwood, or to clear redwood, according to the maker. This price is significantly higher than that of conventional pressure treated decking.
Bay Tree Technologies recommends that PureWood decks be protected with a UV inhibitor, such as products made by Cabot Stain. Without the UV protection, the wood will weather to a silver-gray color over time.