Durability of thermally modified western hemlock lumber against wood decay fungi

IRG/WP 22-40954

G Presley, J Cappellazzi, I Eastin

The chemical modification of wood is gaining popularity as a treatment to increase wood durability in the United States. Further standardization and testing of thermally modified North American species is needed to optimize the production of thermally modified products from regionally available resources. This work measures the impact of thermal modification of western hemlock lumber durability against decay fungi for a single treatment process. Western hemlock lumber was thermally modified using a cycle with temperatures ranging from 80-170ÂșC and was cut into standard 19 mm blocks for testing according to AWPA method E10. Performance of thermally modified wood was measured against two brown rot fungi, Rhodonia placenta and Gloeophyllum trabeum and one white rot fungus, Trametes versicolor over an 8, 12 and 16-week incubation period. Unmodified western hemlock wood, untreated southern pine and copper azole-treated southern pine were included for comparison. Thermal modification resulted in a slight improvement in durability against Gloeophyllum trabeum, but not Rhodonia placenta compared to untreated western hemlock which caused 50.3% and 52.2% mass loss in thermally modified western hemlock after 16 weeks, respectively. T. versicolor caused a 21.2% mass loss after 16 weeks, but this value was not statistically different than untreated western hemlock (p=0.46). For comparison, copper azole-treated southern pine showed only an average of 0% and 15% mass loss when exposed to G. trabeum or R. placenta for 16 weeks, respectively. Together, these data indicate that while there may be some protective effect of thermally modifying western hemlock, further development of treatment processes are needed to improve the durability of thermally modified western hemlock. This study describes durability testing of thermally modified, Tsuga heterophylla (western hemlock) wood using an American Wood Protection Association (AWPA) E10 soil bottle test (AWPA 2020). The test used 19 mm blocks cut from the thermally modified and control western hemlock lumber that was left over following bending strength tests. The test compared the decay resistance of thermally modified western hemlock with untreated western hemlock, untreated southern pine, and southern pine treated with copper azole to UC3B retention levels against two brown rot fungi and one white rot fungus.


Keywords: thermal modification, hemlock, durability, decay

Conference: 22-05-29/06-02 Bled, Slovenia


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