Surface Roughness of Sliced Veneers in Terms of Defects and Wood Structure Variability – Impact of Mild Hydrothermal Treatment

Τhis study deals with the surface roughness and quality of oak sliced veneers and how these characteristics are influenced by the presence of knots, and other defects associated to knots. The variability of roughness is thoroughly examined along the oak stem, exploring also how it differentiates going from one veneer to the adjacent one, cut in different wood depths of the same sawn wood piece in defect and non-defect areas. The expected vertical variability of morphological characteristics did not influence significantly the surface roughness along the stem, which favors the sliced veneers application and performance. The veneers obtained from the edges of the veneer package presented surfaces of high roughness. The smoothest surfaces were recorded in some of the areas on or peripherally of the living intergrown knots. Apart from the cases of large or dead knots that break and result in detrimental cavities, the small live knots do not influence negatively the roughness and therefore, neither the veneer processing demands, nor the overall quality of the final veneer-based product. In order to improve the surface quality of oak sliced veneers and to investigate the response of both defect- and non-defect areas to the hydrothermal modification, two mild and short-term hydrothermal treatments were applied. Among these treatments, only the mildest one (110 ºC) managed to improve significantly the surface quality, concerning both the defect and non-defect areas, while the treatment at 130 ºC did not reveal a significant change of the surface roughness of veneers.