Miloš Pánek

The effect of natural weathering on untreated wood surface

As a result of contemporary ecological and sustainable movements, a number of constructions from wood, as the only renewable building material, is still increasing. In accordance with these trends, wood elements are often left untreated. The presented study is aimed to characterize and compare a surface degradation of untreated wood caused by weathering. Weathering characteristics of softwoods and hardwoods (spruce, pine, Douglas fir, larch, oak, black locust, maple, poplar and alder) during twelve months of exposure in the climatic conditions of Central Europe were determined. All the wood species were characterized by colour and gloss changes and increasing roughness. The lowest discoloration was observed for oak and the highest one for spruce wood, respectively. The lowest changes of roughness were observed for alder, the highest for spruce wood. The depth of colour changes was relatively similar among the softwoods. Regarding hardwoods, it varied more. The values of total colour changes had a significant correlation with the depth values of these colour changes. Maple, alder and poplar samples were characterized by the presence of mould and blue-stain fungi. Douglas fir wood was found to be the most liable for the formation of cracks.

Ultrasonic technique for evaluation of initial stadium of wood degradation in exterior conditions without ground contact

Abstract The experiment evaluate the possibility of using non-destructive measure techniques of the mechanical properties of wood using ultrasonic to determine the initial stages of degradation by biotic and abiotic factors in the outdoors without ground contact. Nine tree species were tested: spruce, pine, Douglas fir, larch, oak, black locust, maple, poplar and alder. Test specimens were exposed to the exterior according to EN 927-3, Prague-Suchdol in the Czech Republic. Measuring changes in velocity of ultrasonic using the apparatus Ultrasonic Timer and moisture content change were measured after 1, 2, 3, 4 and 6 months. Certain ways of detecting the initial stages of damage have been demonstrated to trees oak, larch and spruce. The initial stages of damage by molds at non-durable maple, alder and poplar had not a clear impact on the decrease in the speed of ultrasonic, as well as hairline surface cracks at the Douglas fir.

Colour Stabilization of Oak, Spruce, Larch and Douglas Fir Heartwood Treated with Mixtures of Nanoparticle Dispersions and UV-Stabilizers after Exposure to UV and VIS-Radiation

Colour changes and associated wood degradation in exterior and interior applications influenced by ultraviolet (UV) and visible radiation (VIS) decreases the aesthetic value of the products and shortens the overall life of transparent coatings. The aim of the paper is to achieve colour stabilization of oak, larch, Douglas fir and spruce heartwood via surface treatment with UV stabilizers, hindered amine light stabilizers (HALS), nanoparticles TiO2, ZnO, and mixtures thereof, during exposure to UV and VIS radiation. Colour changes were evaluated during accelerated artificial ageing testing in Xenotest. The distinctly individual character of colour changes in surface treatments due to the underlying wood species was confirmed. A synergistic effect was found when using a combination of active substances compared to substances used individually. The mixture of benzotriazoles with HALS (Tinuvin 5151) in combination with TiO2 and ZnO nanoparticles was confirmed as one of the most effective treatments for colour stabilization of wood due to UV and VIS spectrums.

WATER PERMEABILITY OF EXTERIOR WOOD COATINGS: WATERBORNE ACRYLATE DISPERSIONS FOR WINDOWS

Permeability of coatings for water and water vapor is an important factor in their wood protective function. In this study, the permeability of coatings in terms of liquid water and water vapor absorption and desorption was measured based on different parts of the standard EN 927. This study evaluated the permeability of commercial coating systems and ascertained effects of coating layering on the coating permeability. For this measurement, six different waterborne acrylate dispersions were used as paint on spruce test samples. The results clearly revealed that liquid water and water vapor uptake were affected by coating film thickness, number of coats, and coating composition (producer). It was ascertained that the type of coating pigmentation affected water absorption of coatings and that with a constant coating film thickness, the number of coats affected water vapor absorption and desorption, but not water absorption. Furthermore, it was observed that the number of coats affected the correlation betwe...