Characterization and Monitoring of Surface Weathering on Exposed Timber Structures With a Multi-Sensor Approach

The goal of this work was to understand and model the combined effect of time, geographical location, and exposure on the physical–chemical mechanisms of wood weathering in structures. Series of wooden samples were exposed to natural weathering in seven locations varying in climatic conditions, including Italy and north Germany. The set of samples was exposed for 4 years, collecting representative samples each year. Four exposure directions (north, south, east, and west) were investigated. Measurements of samples included: photogrammetry, near and mid infrared spectroscopy, color, gloss, roughness, and elemental composition (x-ray fluorescence spectroscopy). Results showed that the surface degradation mechanisms caused by weathering were affected by the site of exposure. The wood samples weathered in the Italian sites, in Udine and Macerata, were most degraded. The most significant changes were observed in samples exposed to the south direction. The original algorithm for calculation of “the weathering indicator”, by merging the multi-sensor data and linking these to the surface performance indicators was developed. Finally, the subjective visual assessment by the expert person was compared with parameters obtained by measuring the weathered surfaces with various sensors. A good correspondence between weathering indicator Wind and subjective quality index was established.