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

Efficacy of Hydrophobic Coatings in Protecting Oak Wood Surfaces during Accelerated Weathering

The durability of transparent coatings applied to an oak wood exterior is relatively low due to its anatomic structure and chemical composition. Enhancement of the protection of oak wood against weathering using transparent hydrophobic coatings is presented in this study. Oak wood surfaces were modified using UV-stabilizers, hindered amine light stabilizer (HALS), and ZnO and TiO2 nanoparticles before the application of a commercial hydrophobic topcoat. A transparent oil-based coating was used as a control coating system. The artificial weathering test lasted 6 weeks and colour, gloss, and contact angle changes were regularly evaluated during this period. The changes in the microscopic structure were studied with confocal laser scanning microscopy. The results proved limited durability against weathering of both tested hydrophobic coatings. The formation of micro-cracks causing the leaching of degraded wood compounds and discolouration of oak wood were observed after 1 or 3 weeks of the weathering test. Until then, an oil-based coating film had protected the wood sufficiently, but after 6 weeks the wood was fully defoliated to its non-homogenous thickness, which was caused by the presence of large oak vessels, and by the effects of specific oak tannins. Using transparent hydrophobic coatings can prolong the service life of the exteriors of wood products by decreasing their moisture content. Without proper construction protection against rainwater, the hydrophobic coating itself cannot guarantee the preservation of the natural appearance of wood exteriors

Effect of the Number of UV-Protective Coats on the Color Stability and Surface Defects of Painted Black Locust and Norway Spruce Woods Subjected to Natural Weathering

This paper utilized 12 coating systems, based on an acrylate and a hydrophobic polymer, with the addition of light pigments, nano-sized polyvalent metal (AsS-chelate complex) for ultraviolet protection, and iodopropynyl butylcarbamate fungicide. This study deals with the impact of the number of coats on the color stability and the surface defects of painted black locust (Robinia pseudoacacia L.) and Norway spruce (Picea abies Karst L.) woods after up to three years of natural weathering, at a slope of 45°. The best coating system was created from three coats, which consisted of two pigmented acrylates (PerlColor) and one transparent hydrophobic water-repellent (AquaStop). The total color change, ΔE*, of the weathered surfaces was approximately two times lower when the application involved a pigmented coating system compared with a transparent one. The color stability of the surfaces and their resistance to defects was better when the coating system was applied to black locust wood compared with spruce wood. Smoother surfaces of wood before painting resulted in a higher resistance against cracking and other defects caused by natural weathering; however, the effect of the initial wood roughness on the color stability of painted woods during natural weathering was usually negligible

Effects of Wood Roughness, Light Pigments, and Water Repellent on the Color Stability of Painted Spruce Subjected to Natural and Accelerated Weathering

This study examined the color stability of painted Norway spruce (Picea abies) samples subjected to natural and accelerated weathering, using Duncan’s tests and correlation analyses. The following effects were studied: (1) the different initial roughness of the wood; (2) use of transparent or lightly-pigmented top-coat layers; and (3) the presence of the final water-repellent layer. Natural weathering at a 45° slope in an industrial zone lasted 104 weeks, whereas accelerated weathering in Xenotest with 0.55 W/m2 UV irradiation at 340 nm and sprayed water lasted 12 weeks. The color stability of painted spruce, measured in a CIE-L*a*b* system, was not, in the majority of cases, significantly affected by the initial roughness of the wood, the type of top-coat (WoodCare UV or PerlColor) layer, or presence of the final water repellent (AquaStop) layer. The light pine or larch pigments in the top-coat layers had positive color stabilizing effects. In their presence, the darkening (-L*) and total color differences (E*) of the painted samples dropped ca. 2.5 times during exterior weathering and ca. 5 times during Xenotest weathering. Samples painted with transparent coatings turned a reddish shade (+a*) during the Xenotest, while those exposed to the exterior absorbed dirt and became more blue (-b*)

BACILLUS SUBTILIS FOR IMPROVING THE SPRUCE WOOD IMPREGNABILITY

Impregnation of spruce and other conifers is very difficult due to aspiration of pits in tracheids. In this experiment, freshly cut and instantly debarked Norway spruce logs were pre-treated with the bacterium Bacillus subtilis at their ponding for 1, 3, 6 and 9 weeks under laboratory conditions at 30 °C or under outdoor conditions during the summer at 5 to 35 °C. Significant increases of the permeability and the impregnability of spruce sapwood were observed already after 3 weeks of its ponding due to bacterial attack and opening of pits in tracheids. Applied bio-treatments did not have a significant influence on selected mechanical properties of spruce wood. This method could be effectively used for poles and other round products from spruce or other conifers before their impregnation with preservatives or modification substances. However, its use for squared spruce timbers is not convenient because tracheids in the bacterially treated heartwood zone remained unchanged

Ten Essential Oils for Beech Wood Protection - Efficacy Against Wood-destroying Fungi and Moulds, and Effect on Wood Discoloration

This work analyses the anti-fungal efficacy and stability of 10 essential oils, as well as their colour stability, in wood. The efficacy of oils against the decay fungi Coniophora puteana and Trametes versicolor as well as the moulds Aspergillus niger and Penicillium brevicompactum was evaluated first on filter papers treated with 1, 3.5, 10%, or 100% concentrate, and then on beech wood treated with 10% solutions. Accelerated ageing of treated beech samples was done before mycological tests and consisted of heating, leaching followed by heating, and Xenotest followed by heating. The highest growth inhibition of moulds and C. puteana was caused by thyme, oregano, sweet flag, and clove oils, while the savory and birch oils were less effective. These oils are potentially useful for wood protection against brown-rot fungi and moulds, mostly in interior conditions. The essential oils had only a negligible effect against the white-rot fungus T. versicolor, which was more apparent after previous ageing of wood. Some essential oils with a yellow tone (birch, oregano, sweet flag, savory, and tea tree oils) significantly changed (p<0.05) the natural colour of beech wood, but the new colours were relatively stable and underwent only mild changes after accelerated ageing in Xenotest

Influence of different exposition of larch wood facade models on their surface degradation processes

Wood, as a building material, is nowadays more often used outdoors. From the point of view of environment care, wood constructions and use of renewable materials belongs between modern increasing trends in industry. Wooden facades, more often used without surface treatment, are the important part of this trend. In Central Europe, European larch (Larix decidua) and Siberian larch (Larix sibirica) are especially popular materials for wooden facade elements. The aim of this study is to characterize the surface degradation of untreated facade models from both European and Siberian larch wood. The wood species, orientation to the sides of the world and construction type of the facade were the evaluation factors, which were regularly examined during 24 months of outdoor exposure via measuring the changes of surface colour, gloss, wettability and visual appearance in the form of cracks and resin leaking. The influence of all evaluated factors on the measured properties was determined. The results of this work can help to proper use of untreated larch wood on facade elements in practice

Comparison of Selected Properties of Shellac Varnish for Restoration and Polyurethane Varnish for Reconstruction of Historical Artefacts

At present, many historical artefacts and furniture are only reconstructed and not restored. They are preserved in terms of material reparation, but their historical value decreases significantly. This work is focused on the comparison of the resistance of high-gloss polyurethane varnish with traditional shellac varnish. The varnishes were applied to oak wood and exposed to interior artificial accelerated ageing in Xenotest. Before and after ageing, cold liquid-resistance tests were performed on the tested specimens and gloss, colour, and adhesion were also evaluated. The structures of the surfaces were also analysed using a confocal laser scanning microscope. As expected, polyurethane varnish was much more durable than shellac varnish. Interestingly, shellac varnish was fairly resistant to water at the beginning, but this resistance was greatly reduced after artificial accelerated ageing. This illustrates the importance of sheltering the shellac treated artefacts in stable temperature-humidity conditions with the least possible effect of solar radiation

Volatile Organic Compounds (VOCs) from Wood and Wood-Based Panels: Methods for Evaluation, Potential Health Risks, and Mitigation

Volatile organic compounds (VOCs) are contained in various construction materials and interior equipment. Their higher concentrations in the indoor air are associated with negative effects on human health and are disputed in terms of health risk, since people spend a considerable part of their lifetime indoors. Therefore, the presence of VOCs in indoor air is a case of concern regarding sick building syndrome (SBS). From a historical point of view, wood and wood-based panels represent a widely used material. Nevertheless, wood appears to be nowadays a product and a material of a sustainable future. Depending on wood extractives&rsquo; composition and an abundance of diverse wood species, different profiles of volatiles are emitted. In case of wood-based panels, the impact of adhesives and additives that are essentially applied aiming to adjust the panels&rsquo; properties is even enriching this cocktail of chemicals. This paper comprises the issue of VOCs emitted from wood and wood-based panels. The most abundant VOCs were summarized. The options of VOCs for analytical determination from these matrixes are described with their benefits and limitations