Hardness Values for Thermally Treated Black Ash


  • Mathew A. Leitch


Thermally modified wood, thermowood, Janka ball hardness test, undervalued, underutilized, value-adding, black ash


The objective of this study was to analyze the effect of a thermal treatment on the hardness of a Boreal hardwood species. As an undervalued and underutilized tree in Canada, black ash (Fraxinus nigra Marsh.) was selected as one that could potentially benefit from this process. The wood was processed runs in a new high-temperature kiln system being developed in northwestern Ontario, Canada, by Superior Thermowood®. During the processing, the wood deepened in color from a light brown to a darker brown, similar to that of walnut wood. Defect-free samples of Thermowood black ash were collected from two high-temperature runs (200°C wood temperature) and tested for hardness. Using the Janka ball hardness test, thermally modified black ash displayed average hardness values at 8% MC (5700 N), 43% greater than the controls and in the same range as published for untreated wood (5400 - 6000 N). With an improvement in the black ash aesthetic appearance combined with the slight increase in hardness, this species is well suited to be utilized in high-value markets, including flooring and fine furniture.


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