The influence of wood coatings on the moisture buffering capacity of CLT and the indoor environment
Chapter, Doctoral thesis, Conference object
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The objective of the study was to determine the influence of wood coatings for CLT on the moisture buffering capacity and the indoor environment regarding relative humidity and heating demand. Based on the results of a previous screening of a wide range of coatings, three commercial products were chosen: a flooring oil, an alkyd-based interior wall stain and a fire-retardant stain that were considered to provide both, i) high water vapor permeability to maintain wood’s hygroscopicity, and ii) adequate protection of CLT under storage, transport, installation and service. A climate chamber test revealed a good moisture buffer capacity of untreated CLT and a limited one of CLT cladded with gypsum. CLT’s glue lines in the frontal plane were not found to affect moisture dynamics. The flooring oil and the wall stain reduced the practical moisture buffer value by 39% and 10%, respectively, as compared to the uncoated CLT. CLT coated with the fire-retardant stain had an even higher practical moisture buffer value than uncoated wood, which is explained by the stain’s pronounced hygroscopicity. In all elements tested in a heat flux experiment, the theoretical Uvalues were higher than the experimentally obtained and simulated values. Hygrothermal energy simulations using a room of 50 m2 as ‘reference model’ showed that wood’s moisture buffer capacity is beneficial for the indoor environment, by means of passive regulation of RH and lower energy demand for humidification and dehumidification.