**Ladislav Reinprecht \* and Miroslav Repák**

Department of Wood Technology, Faculty of Wood Sciences and Technology, Technical University in Zvolen, T. G. Masaryka 24, SK-96001 Zvolen, Slovakia; xrepak@tuzvo.sk

**\*** Correspondence: reinprecht@tuzvo.sk; Tel.: +421-45-520-6383

Received: 5 November 2019; Accepted: 26 November 2019; Published: 2 December 2019

**Abstract:** The European beech (*Fagus sylvatica* L.) wood was thermally modified in the presence of paraffin at the temperatures of 190 or 210 ◦C for 1, 2, 3 or 4 h. A significant increase in its resistance to the brown-rot fungus *Poria placenta* (by 71.4%–98.4%) and the white-rot fungus *Trametes versicolor* (by 50.1%–99.5%) was observed as a result of all modification modes. However, an increase in the resistance of beech wood surfaces to the mold *Aspergillus niger* was achieved only under more severe modification regimes taking 4 h at 190 or 210 ◦C. Water resistance of paraffin-thermally modified beech wood improved—soaking reduced by 30.2%–35.8% and volume swelling by 26.8%–62.9% after 336 h of exposure in water. On the contrary, its mechanical properties worsened—impact bending strength decreased by 17.8%–48.3% and Brinell hardness by 2.4%–63.9%.

**Keywords:** beech; paraffin; thermal modification; fungi; swelling; mechanical properties
