The surface carbonisation of wooden materials is a traditional Japanese technique known as Yakisugi or Shou Sugi Ban. Yakisugi-treated Japanese cedar is reputed to exhibit enhanced properties, including increased durability, weather resistance, fire resistance, and reduced water absorption (Buksans et al., 2021; Kymäläinen et al., 2020; Kurimoto et al., 2002; Šeda et al., 2021)). However, some studies such as Hasburgh et al. (2021) report less pronounced or inconsistent changes in material properties following surface charring. Beyond its functional aspects, carbonized wood is valued for its aesthetic appeal and is increasingly being used in Europe, particularly for façade applications. A prominent example is the Müritz Museum in Waren, Germany. Nevertheless, the traditional Yakisugi process is largely artisanal in nature and not readily adaptable to industrial-scale production. Industrial implementation poses several challenges, such as achieving a uniformly distributed char layer and ensuring sufficient mechanical stability of the carbonized surface.
One promising approach to address these challenges is the use of a heated metal plate instead of an open flame—a method known as contact charring (Kymäläinen et al., 2017, 2023; Leich & Pfriem, 2025). In the present study, however, it is explored whether the application of commonly used fire retardants could influence the carbonization process in a way that promotes the formation of a stable char layer.
To this end, specimens of spruce (Picea abies) were treated with diammonium hydrogen phosphate (DAP) and magnesium chloride (MgCl₂). Untreated spruce served as reference. The resulting carbonized surfaces were then assessed, characterized and compared determine the charcoal layer thickness, the density profile of the charred wood and the contact angle to evaluate the surface.
Keywords: surface carbonization, wood modification, surface properties
Authors
Tom Franke
Bern University of Applied Sciences – Department of Architecture,Wood and Civil Engineering Biel/Bienne,Switzerland
Elena Nedelkoska
Bern University of Applied Sciences – Department of Architecture,Wood and Civil Engineering Biel/Bienne,Switzerland
Paul Baustert
Bern University of Applied Sciences – Department of Architecture,Wood and Civil Engineering Biel/Bienne,Switzerland
Liam Dorm
Bern University of Applied Sciences – Department of Architecture,Wood and Civil Engineering Biel/Bienne,Switzerland
Pius Giordano
Bern University of Applied Sciences – Department of Architecture,Wood and Civil Engineering Biel/Bienne,Switzerland
Benyamin Khabbaz
Bern University of Applied Sciences – Department of Architecture,Wood and Civil Engineering Biel/Bienne,Switzerland
Theyge Nenz
Bern University of Applied Sciences – Department of Architecture,Wood and Civil Engineering Biel/Bienne,Switzerland
Emanuel Nwachukwu
Bern University of Applied Sciences – Department of Architecture,Wood and Civil Engineering Biel/Bienne,Switzerland
Naim Solthorres
Bern University of Applied Sciences – Department of Architecture,Wood and Civil Engineering Biel/Bienne,Switzerland
Thomas Volkmer
Bern University of Applied Sciences – Department of Architecture,Wood and Civil Engineering Biel/Bienne,Switzerland
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