Improvement in Sugi Wood Hardness and Density Through a Thermo-Hydro-Mechanical Densification Process

Sugi (Cryptomeria japonica D. Don) is an important timber resource for the Portuguese forest and construction sectors. Nevertheless, its relatively low density is associated with reduced stiffness and mechanical strength, which limits its suitability for structural applications. In addition, for non-structural uses such as flooring and cladding, its low surface hardness and poor fastener-holding capacity constitute significant disadvantages, restricting its competitiveness in higher-value applications. To address these limitations, a study was undertaken to assess the feasibility of increasing the density of Sugi timber through a densification process. The objective was not only to enhance its density, but also to improve its hardness and, consequently, its suitability for a wider range of construction applications. Thermo-hydro-mechanical densification increased the density of sugi wood from approximately 350 to 500 kg/m3 and improved hardness from values below 6.4 N/mm2 to values above 10 N/mm2, while maintaining good dimensional stability under indoor conditions. These results demonstrate the potential of densified sugi for multilayer parquet flooring and other non-structural interior applications.