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Check development on jack pine logs in Eastern Canada
2001 - IRG/WP 01-10387
Logs in storage are subject to check damage. The severity of the problem may vary with various environmental and storage conditions. In this study, an investigation was conducted on the development of checks in debarked and bark-on jack pine (Pinus banksiana) logs in Eastern Canada. In the summer of 1999, jack pine trees were felled, logs were debarked and stored in a sawmill yard. The logs were inspected and sampled every 2 to 4 weeks. The moisture content and the amount and depth of checks presented in each log were determined. Bark-on logs, stored in sunny and shaded environments served as controls. The results showed that the moisture content of debarked logs dropped rapidly, whereas the humidity of bark-on logs stored in a shaded environment decreased much slower. More checks were found on debarked logs than on bark-on ones. On debarked logs, the average number and depth of checks increased proportionally with the duration of storage. However, formation of the deepest check did not correlate with storage time. Fewer checks were detected on logs with intact bark, especially on those stored in the shade.
Dian-Qing Yang, R Beauregard


Evaluation of surface cracks on wood – physical assessment versus subjective sensation
2017 - IRG/WP 17-20617
In the presented studies from the University of Goettingen (Study I) and the University of Hannover (Study II), the assessment of cracks with different methods and their acceptance in general as well as depending on different target groups are investigated. The aim was to determine which factors are relevant for a crack evaluation and which visual impression of a wooden surface is tolerable for consumers. In both studies, the cracks were classified according to ISO 4628-4 (2004). In addition to the evaluation according to the standard, the specimens were evaluated in Study I according to a “school grade system”. The tolerance against cracks and discolouration on wooden surfaces was requested in study II during an interview survey at a DIY-market. The results showed that the number of cracks as criterion for the quality assessment was not decisive, but primarily the crack size. Cracks in claddings are more acceptable than cracks in decking. Furthermore, a uniform discolouration was more tolerated than a stained appearance of wooden surfaces. Both studies showed that the assessment of the quality of a wood surface is strongly dependent on the quality of the starting material. A wood surface with poor starting quality is generally less tolerated with regard to crack formation and discolouration. The estimation of the visual appearance of the test specimens according to a “school grade system” proved to be an adequate, complementary method for assessing the crack performance of wood.
A Gellerich, C Brischke, L Emmerich, L Meyer-Veltrup, P Kaudewitz


Weathering protection of European hardwoods through double modification
2017 - IRG/WP 17-30715
Beech and poplar were thermally modified, treated with melamine resin and both treatments were combined. The weathering performance (cracks and general appearance) of modified beech and poplar was assessed in natural weathering and correlated to material properties such as work in bending (WB) and Brinell hardness. In addition, the equilibrium moisture content after exposure of 12 months and subsequent climatization was evaluated. Melamine treated beech and thermally modified poplar performed best while still showing serious cracks. The melamine treatment increased the equilibrium moisture content, indicating a rather hygroscopic behaviour of the resin. All treated groups showed increased moisture contents after weathering and subsequent climatization. The thermal and melamine treatment decreased the WB substantially. The melamine treatment of the thermally modified wood (double modification) did not further decrease the WB. WB as an indicator of brittleness could not explain the cracking behaviour. Thermal modification decreased the Brinell hardness, whereas melamine treatment increased it. The increased Brinell hardness of melamine treated groups and the double modified groups can be accounted for the stabilized surfaces without erosion.
G Behr, A Gellerich, S Bollmus, H Militz