The importance of choosing building materials with a low environmental impact increases with increasing energy efficiency of buildings. Wood is an economical material but in use it degrades due to biotic factors. It is vital to develop surface treatments that reduce the environmental load from maintenance and replacement of components. Wood char is a chemically stable, hydrophobic material that could be used as surface “treatment” for cladding boards on building façades. The methods for creating a charred surface layer include open fire, gas flame, and hot plate. Using open fire or flame will flash burn the surface, and because of its heterogeneity, a wooden board will include differently charred regions formed by a variety of temperatures. A flame charred siding will also weather and fade during its lifetime. The hot plate method offers a careful control of process conditions, namely the peak temperature, and avoids heterogeneity from flaming. But will a surface treated in this manner be resistant to weathering? This study aims to compare gas flame charred and hot plate charred surfaces in terms of service durability. The investigated properties are surface wettability, i.e. hydrophobicity towards liquid water, thickness of char layer as well as the pyrolysis layer to predict stability, and transmission of heat inside the wood in certain treatment conditions. The presented results are preliminary and part of a larger project aiming to quantify weathering-related properties of wood surfaces charred in different manners.
Keywords: surface treatment, wood char, weathering resistance
Authors
M. Kymäläinen
L. Rautkari
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