The purpose of this study on tamarack (Larix laricina) was to propose a drying technique adapted to the end use, to document the colour change after drying, and to assess the rot resistance of the various drying processes used. This study was divided into two parts. In the first part, 5/4’’ thick lumber was dried using superheated steam/vacuum (SS/V) drying in order to compare drying results with the results of a study conducted at Université Laval. The Université Laval study compared drying results obtained with three conventional drying schedules: high temperature (115 °C), elevated temperature (90 °C), and standard temperature (82 °C). The study compared drying time, final quality, colour change, and rot resistance. The second part of the study involved drying 7/4’’ thick lumber using SS/V drying.
It was clearly shown that drying process does not affect rot resistance of tamarack. However, drying process and operating temperature affect colour after drying. High temperature drying resulted in the greatest post-drying colour change. The SS/V process provided post-drying results that closely matched those before drying. The drying time obtained from the best SS/V test, with a time/quality trade-off, was longer than in the Université Laval high-temperature conventional test (0.9 factor). Compared to conventional drying schedules, the SS/V process was 1.4 times faster than the elevated temperature schedule, 2 times faster than the standard temperature schedule, and 3.4 times faster than schedules used in the industry.
Drying times required to reach a final moisture content of approximately 12% in the four 7/4” lumber tests ranged from 132.2 hours to 175 hours. Compared to current industrial results, drying by SS/V is approximately 2.6 to 3.1 faster. Warping was better controlled during the 7/4’’ tests. Winter conditions during the tests made it difficult to maintain conditions in the SS/V kiln. Nonetheless, the use of concrete dead loads on the charges and high temperature conventional kiln drying appear to provide good possibilities for Canadian manufacturers.
NRCan Value to Wood Program which discusses Larix laricina; Seasoning - Vacuum, Steam and Kiln drying