Wood defects during industrial-scale production of thermally modified Norway spruce and Scots pine

Michael Altgen, Stergios Adamopoulos, Holger Militz*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

11 Citations (Scopus)


This research investigates wood defects, particularly the formation of surface cracks, during the production of thermally modified wood and its exposure to cyclic moisture changes. Boards of Norway spruce and Scots pine originating from different steps within the production of ThermoWood® were collected and wood defects were investigated at macroscopic and microscopic scale. Subsequently, the wood was exposed to capillary wetting cycles to record its sensitivity towards cracking. After the modification process, typical anatomical defects of conventional kiln-drying became more frequent and severe, with the magnitude being to some extent depending on the presence of defects in the raw material. At microscopic scale, damages to ray parenchyma and epithelial cells as well as longitudinal cracks within the cell walls of earlywood tracheids were evident in thermally modified wood. Despite a lower water uptake and higher dimensional stability, thermally modified wood was more sensitive to surface cracking during wetting cycles than unmodified wood, i.e. at the outside face of outer boards (near bark). For limiting surface cracking of thermally modified wood during service life, the use of high-quality raw material, the exposure of the inside face of the boards (near pith) and the application of a surface coating are considered beneficial.

Original languageEnglish
Pages (from-to)14-23
Number of pages10
JournalWood Material Science and Engineering
Issue number1
Publication statusPublished - 1 Jan 2017
MoE publication typeA1 Journal article-refereed


  • cell-wall features
  • light microscopy
  • SEM
  • surface cracks
  • Thermal modification
  • wetting cycles

Fingerprint Dive into the research topics of 'Wood defects during industrial-scale production of thermally modified Norway spruce and Scots pine'. Together they form a unique fingerprint.

Cite this