Heat-treatment of Sitka spruce, Japanese larch and lodgepole pine panelling

The results of the latest evaluation of test panels representing a cladding application and constructed using heat-treated Sitka spruce, lodgepole pine and Japanese larch, exposed in a field trial in Clonmel are reported and some earlier mechanical property results are summarised. Most timber had been subject to the Finnish Thermowood process with smaller amounts of timber treated in the Netherlands using the Platowood and Lignius processes. Control panels using un-treated spruce and western red cedar were also exposed and the trial is now concluding in its eleventh year. Application of the previously described scoring system using criteria such as colour retention, numbers of splits and defects, nail staining and overall appearance has also continued. Untreated spruce controls are showing significant decay, but no decay has been observed in the heat-treated materials, which also show higher dimensional stability. Although the heat-treated panels are much better than the spruce controls they do not equal the overall weathering behaviour of the cedar control panels. Timber from the Thermowood process continues to show the best performance of the heat-treated materials and this is considered to be substantially attributable to it being better quality selected timber.

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