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

Raised grain occurring on wood surfaces after the application of a waterborne varnish was felt by human touch because of protruding peaks and a certain amount of materials in the core of the roughness profile. This tactile sensation was correlated with specific roughness parameters. Characteristics of a finished surface quality that is acceptable to consumers were determined.

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.

Raised grain, Topographic parameters, Waterborne varnish, Visuo-tactile analysis, Planing Sanding

Ramanakoto, M.F., Ramananantoandro, T., Eyma, F. et al. Annals of Forest Science (2019) 76: 26.

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Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request in the Zenodo repository: Ramanakoto MF, Ramananantoandro T, Eyma F, CastaniƩ B (2018). Data about the visuo-tactile preferences of finished surface quality by French Consumers as regards raised grain on woods. V1. Zenodo. [Dataset].

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