Visuo-tactile and topographic characterizations of finished wood surface quality by French consumers and industrials: acceptability thresholds for raised grain

Abstract

Context: Raised grain occurs on wood surfaces after the application of a waterborne varnish and forces manufacturers to sand the surfaces between coats. Actually, little research has characterised this phenomenon and no techniques have been discovered to avoid its occurrence. Aims: This study aims to identify the topographic parameters that explain the visuo-tactile sensation of raised grain and to define a finished surface quality acceptable to consumers and industry. Methods: Oak (Quercus robur L.) and beech (Fagus sylvatica L.) wood surfaces were planed and sanded in order to have various levels of raised grain. Visuo-tactile analyses were carried out on surfaces having received one coat of varnish to characterise raised grain and having two coats to characterise the acceptable finished surface quality without sanding. Topographic parameters were measured on each type of varnished surface and correlated with the visuo-tactile scores. Results: Raised grain was characterised by the visuo-tactile sensation of protruding peaks and a certain amount of material in the core of the roughness profile for both wood species. Industrials overestimated the surface quality required by consumers. Thresholds of topographic parameters were determined to define acceptable finished surface quality. Conclusion: These findings allowed objective criteria to be defined for describing raised grain and to help industries to optimise their wood machining and finishing processes.