• Zuzana Vidholdová Technical University in Zvolen
  • Ladislav Reinprecht Technical University in Zvolen
  • Miloš Pánek Czech University of Life Sciences Prague


spruce , pine, thermowood, weathering, colour, gloss, roughness, mould resistance


Products from thermally modified wood used outdoors should be stable against sun, rain, wind, and biological agents. The effect of 1- to 24-month outdoor weathering of the Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) thermally modified woods “Thermo-D produced in Oy Lunawood Ltd Finland” (TWs) on their selected surface properties – colour, gloss, roughness, and mould resistance is analysed in the paper. With prolonged weathering, the surfaces of both Thermo-D wood samples lost their original yellow-red shadow. They continuously turned greyer – in the CIE L*a*b* colour system, they obtained greener and bluer colours, together with the logarithmic increase in the total colour difference ΔE*ab. Surfaces of both Thermo-D wood samples within the first four months of outdoor weathering turned much lighter with a higher gloss. However, they got darker and matter due to adsorbing soot and dirt. Similar changes, i.e., as in the lightness and gloss, occurred in the roughness of weathered Thermo-D woods, which firstly decreased and subsequently increased with further prolongation of weathering.  Moulds Aspergillus niger and Penicillium brevicompactum, in all cases, intensively attacked spruce and pine wood – natural wood, Thermo-D wood, weathered natural wood, weathered Thermo-D wood.


Ahola, P., Jämsä, S., Viitanen, H., Viitaniemi, P., 2002. Mould and blue stain on heat treated wood. Proceedings of Cost Action 18 Meeting, Portugal, 4 April 2002.

Ayadi, N., Lejeune, F., Charrier, B., Merlin, A., 2003. Color stability of heat-treated wood during artificial weathering. Holz als Roh - und Werkstoff 61, 221–226.

Baysal, E., Degirmentepe, S., Şimşek, H., 2014. Some surface properties of thermally modified Scots pine after artificial weathering. Maderas. Ciencia y tecnología 16, 355–364.

ČSN 49 0604: 1980. Ochrana dřeva. Metody stanovení biocidních vlastností ochranných prostředků na dřevo. Úřad pro normalizaci a měření: Praha, Česká republika,1980.

Deka, M., Humar, M., Rep, G., Kričej, B. Šentjurc, M., Petrič, M., 2008. Effects of UV light irradiation on colour stability of thermally modified. copper ethanolamine treated and non-modified wood: EPR and DRIFT spectroscopic studies. Wood Science and Technology 42(1), 5–20.

Evans, P.D., Urban, K., Chowdhury, M.J.A., 2008. Surface checking of wood is increased by photodegradation caused by ultraviolet and visible light. Wood Science and Technology 42(3), 251–265.

EN 927–3: 2006 Paints and varnishes - Coating materials and coating systems for exterior wood - Part 3: Natural weathering test. European Committee for Standardization: Brussels, Belgium, 2006.

EN ISO 2813:2015. Paints and Varnishes, Determination of Gloss Value at 20°, 60° and 85°; European Committee for Standardization: Brussels, Belgium, 2015.

EN ISO 4287:1998/AC. Geometrical product specifications (GPS). Surface texture. Profile method. Terms, definitions and surface texture parameters. European Committee for Standardization: Brussels, Belgium, 1998.

EN ISO 4288:1997. Geometrical product specifications (GPS) - Surface texture: Profile method - Rules and procedures for the assessment of surface texture. European Committee for Standardization: Brussels, Belgium, 1997.

Feist, W.C., 1990. Outdoor wood weathering and protection. In: Rowell, R.M., Barbour, J.R. (eds) Archaeological wood—properties. chemistry. and preservation. Adv Chem Ser 225. Am Chem Soc. Washington. DC. USA.

Hill, C.A.S., 2006. Wood modification: Chemical, thermal and other processes. John Wiley & Sons. Chichester. UK.

Hon, D.N.S., Chang, S.T., 1984. Surface degradation of wood by ultraviolet light. Journal of Polymer Science: Polymer Chemistry Edition 22(9), 2227–2241.

ISO 7724-3: 1984. Paints and Varnishes—Colorimetry—Part 3: Calculation of Colour Differences; International Organization for Standardization: Geneva, Switzerland, 1984.

Jämsä, S., Ahola, P., Viitaniemi, P., 2000. Long-term natural weathering of coated Thermowood. Pigment & Resin Technology 29, 68–74.

Jirouš-Rajković, V., Miklečić, J., 2021. Enhancing weathering resistance of wood - A review. Polymers 13, 1980.

Kropat, M., Hubbe, M.A. and Laleicke, F., 2020. Natural, accelerated, and simulated weathering of wood: A review. BioResources 15(4), 9998.

Kržišnik, D., Lesar, B., Thaler, N., Humar, M., 2018. Influence of natural and artificial weathering on the colour change of different wood and wood-based materials. Forests 9, 488.

Kucuktuvek, M., Baysal, E., Turkoglu, T., Peker, H., Gunduz, A., Toker, H., 2017. Surface characteristics of Scots pine wood heated at high temperatures after weathering, Wood Research 62(6), 905–918.

Kúdela, J., Ihracký, P., 2014. Influence of diverse conditions during accelerated ageing of beech wood on its surface roughness. Acta Facultatis Xylologiae Zvolen res Publica Slovaca 56(2), 37.

Meyer, R.W. Kellogg, R.M., 1982. Structural uses of wood in adverse environments. Van Nostrand Reinhold Company. New York. USA.

Niklewski, J., van Niekerk. P.B., Marais. B.N., 2022. The effect of weathering on the surface moisture conditions of Norway spruce under outdoor exposure. Wood Material Science & Engineering, 1–11.

Nuopponen, M., Wikberg, H., Vuorinen, T., Maunu, S.L., Jämsä, S., Viitaniemi, P., 2004. Heat-treated softwood exposed to weathering. Journal of Applied Polymer Science 91, 2128–2134.

Pandey, K.K. 2005. Study of the effect of photo-irradiation on the surface chemistry of wood. Polymer Degradation and Stability 90(1), 9–20.

Pánek, M., Reinprecht, L., 2014. Colour stability and surface defects of naturally aged wood treated with transparent paints for exterior constructions. Wood Research 59(3), 421–430.

Reinprecht, L., Vidholdová, Z., 2008.Termodrevo – príprava, vlastnosti, aplikácie (Thermowood – preparation, properties, applications). Technická univerzita vo Zvolene, Slovak republic.

Reinprecht, L., 2016. Wood deterioration. protection and maintenance. Chichester: John Wiley & Sons. Ltd., UK.

Reinprecht, L., Repák, M., 2022. Beech wood thermally modified in the melt of polyethylene glycol. BioResources 17(01), 652-672. 10.15376/biores.17.1.652-672

Sandberg, D., Kutnar, A., Karlsson, O., Jones, D., 2021. Wood modification technologies – Principles, sustainability, and the need for innovation. CRC Press, Taylor and Francis Group, LLC, Oxon, UK.

Srinivas, K., Pandey, K.K., 2012. Photodegradation of thermally modified wood. Journal of Photochemistry and Photobiology B: Biology 117, 140–145.

Tomak, E.D., Ustaomer, D., Ermeydan, M.A., Yildiz, S., 2018. An investigation of surface properties of thermally modified wood during natural weathering for 48 months. Measurement, 127, 187–197.

Ugovšek, A., Šubic, B., Starman, J., Rep, G., Humar, M., Lesar, B., Thaler, N., Brischke, C., Meyer-Veltrup, L., Jones, D., Häggström, U., 2019. Short-term performance of wooden windows and facade elements made of thermally modified and non-modified Norway spruce in different natural environments. Wood Material Science & Engineering 14(1), 42–47.

Yildiz, S., Yildiz, U. C., Tomak, E. D., 2011. The effects of natural weathering on the properties of heat-treated alder wood. BioResources 6(3), 2504–2521.

Zink, P., Fengel, D., 1989. Studies on the colouring matter of blue-stain fungi part 2. Electron microscopic observations of the hyphae walls. Holzforschung 43 (6), 371–374.




How to Cite

Vidholdová, Z., Reinprecht, L., & Pánek, M. (2023). THE EFFECT OF OUTDOOR WEATHERING OF THERMALLY MODIFIED SPRUCE AND PINE WOODS ON THEIR SURFACE PROPERTIES. Acta Facultatis Xylologiae Zvolen, 65(1), 23–34. Retrieved from