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.

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