Although there is a global awareness that the exploitation of non-renewable materials is unsustainable, there has been limited interest in fully utilizing natural, renewable resources like wood and its products because of the service durability concerns. One such issue is the aesthetical degradation of wooden facades due to the impact of weathering. This research was carried out as an international cooperation project to ascertain the weathering resistance of bio-based façade materials under the Estonian climate. In total, 120 bio-based façade materials obtained from 31 different companies, universities and research institutions from 17 countries were investigated. The specimens were placed on an exposure rack, inclined at an angle of 45° located at 59°23′50.6″ N 24°39′24.0″ E and then subjected to accelerated natural weathering for 2 years. Parameters such as precipitation, UV index, temperature and relative humidity were measured during the period of the natural weathering. The influence of the weathering on the colour change and cracks on the surface of test specimens was evaluated using Minolta Chroma Meter CR-121 (Konica Minolta INC., Tokyo, Japan) and Avongard Check Width Gauge (Avongard Ltd., Gloucestershire, UK), respectively. The results showed that the untreated natural wood façade materials presented the least resistance to weathering, while 63 of the tested materials developed checks. The outcome of this study is essential to the optimization of software-simulating changes in the appearance of façade materials in outdoor conditions.
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