TMT, or Thermally modified timber, is wood that goes through a 3-stage kiln process using high temperature and taking from 24-72 hours to complete a full cycle. During the high temperature phase, the wood is protected from combustion by using steam. In that time, the moisture of the wood is almost completely removed and added back to a precise amount. The natural acids and sugars are modified from the extreme heat which changes the physical structure of the wood. The wood’s ability to absorb moisture is declined making it less prone to rot and decay. The equilibrium moisture content (EMC) of the wood decreases. This means the swelling and shrinking of the wood material due to moisture variations can be reduced by up to 60% as compared to unmodified wood. The most apparent change is that the wood darkens throughout, giving domestic wood the look of desirable imported wood.
The temperature in the kiln is raised rapidly to around 100˚C (212˚F), affecting thenatural composition of the wood. Steam is introduced to prevent the wood from checking in the high heat. The moisture content of the wood is reduced from 15-20% down to nearly zero.
One peak temperature is resulting in a light cook, 190˚C (374˚F), and the other is the dark cook at 210˚C (415˚F). The higher and longer the heat, the darker the wood becomes throughout. Steam is used to prevent the wood from burning in the high temperatures.
Cooling & Re-Conditioning
The temperature is reduced by spraying water onto the wood and cooling. Conditioning and re-moistening take place to bring the wood moisture content around 4-6%
The color of wood will darken in tone through the thermal modification process. It is important to understand that it is a natural product and the grain, original color variances and characteristics of the wood still are present. The wood is darkened throughout so any sanding or refinishing will bring the wood back to the original color without staining. In an exterior environment TMT products do move to gray when unfinished. Finishes with UV inhibitiors help slow this process similar to non-modified products. The color change of the thermally modified wood is especially useful in the flooring industry since it can be used to emulate tropical wood species.
AWCo products are an excellent natural option for wood applications for the interior and exterior. Thermally modified wood is suited for siding, flooring, decking, window and door manufacturing and much more. Products made of thermally modified wood will have limited expansion and contraction and will still take stain and paint like standard wood products.
Thermally modified wood can be used in an abundant array of applications, though some of the most popular are in external applications where moisture and humidity would compromise a lesser grade material.
Improved aesthetics and durability can be reached with many indigenous wood species to replace more expensive tropical wood species and move to more environmentally conscious domestic source.
AWCo is based in Duluth, Minnesota and works with North Central USA suppliers to bring you uncompromised quality in harvest, modification, and millwork. The raw goods harvested for AWCo products come from sustainably managed forests. Minnesota Department of Natural Resources has been recognized as a leader for forest stewardship by FSC and SFI third party certification bodies as the largest single forest management certificate in the nation. AWCo and its partners are aligned geographically and philosophically with the goals of responsible resource management. The heat and steam process used to modify the wood creates a value added product without the use of chemicals.
After wood has been thermally modified its properties are more stable than standard kiln dried wood. The swelling and shrinking ofwood due to moisture variations can be reduced by up to 60%. After the modification process, the physical structure of the wood is changed permanently. Because of these changes in the structure of the wood, its ability to absorb moisture from the surrounding environment greatly declines, making it more durable than untreated wood against biological damages such as decay caused by brown rot and fungus. Like unmodified wood, uncoated thermally modified wood will turn a grey weathered color over a period of time when exposed to direct sunlight. To attain the best biological durability, thermally modified wood should be surface coated.