Decay resistance of softwoods and hardwoods thermally modified by the Thermovouto type thermo-vacuum process to brown rot and white rot fungi

Softwoods (SW, spruce and fir) and hardwoods (HW, ash and beech) were thermally modified by the thermo-vacuum (Termovuoto) process for 3-4 h in the temperature range 160-220 degrees C (TMW160-220 degrees C) and their fungal durability were examined in soil-block tests with two brown rot (BR, Postia placenta, Gloeophyllum trabeum) and two white rot (WR, Pycnoporus sanguineus, Phlebia radiata) fungi. SW-TMW160-220 degrees C were exposed to P. placenta and P. sanguineus and HW-TMW190-220 degrees C to all fungal species. Considerable improvement (durability class 1-3) in decay resistance was only achieved for SW-and HW-TMW 220 degrees C. Thermal modification (TM) below 200 degrees C influenced decay resistance negatively in case of some fungal species applied for both SW and HW. Judged by the durability class, decay resistance was higher in HW- than in SW-TMW at high TM temperature. Behavior of TM differed significantly between ash (ring-porous HW) and beech (diffuse-porous HW). A comparison between results of soil-and agar-block tests on Termovouoto wood demonstrated that the influence of testing method in terms of assignment to durability classes is not significant.