Maintenance procedures of different wood coating systems were studied in field exposure trials with coated balcony constructions. Maintenance coatings were applied on one half of each of the balcony parts after 18 months and assessed after 24 months of total exposure time. It was found that the opaque white coating systems were the most durable ones reaching long intervals of required maintenance. For systems with lower durability on the maintained surfaces further degradation of the coatings was prevented. Different characteristics were observed for film forming and non film forming semi-transparent varnishes. Definitions of a series of limit states for coating systems on wood were suggested including esthetical limits and three levels of durability limits. Film forming coatings can reach two durability limits, i.e. the maintenance interval and the renovation interval. For non film forming coatings there is only one limit state of coating durability where maintenance is needed. The third durability limit is related to the coated substrate, i.e. the wood component, by the onset of decay in wood. Wartungsmaßnahmen von verschiedenen Beschichtungssystemen für Holz wurden in Freilandbewitterungsversuchen mit beschichteten Balkonkonstruktionen untersucht. Wartungsanstriche wurden auf eine Hälfte jedes Balkonteiles nach 18 Monaten Bewitterung aufgetragen und nach 24 Monaten eine Beurteilung durchgeführt. Die deckend weißen Beschichtungssysteme waren am dauerhaftesten und erreichten lange Wartungsintervalle. Bei Systemen mit geringerer Dauerhaftigkeit wurde auf den gewarteten Flächen ein Fortschreiten von Schäden verhindert. Bei filmbildenden und nicht filmbildenden Beschichtungen wurden unterschiedliche Eigenschaften beobachtet. Definitionen von Grenzzuständen von Holzbeschichtungen wurden erstellt und beinhalten ästhetische Grenzen und drei Stufen von Dauerhaftigkeitsgrenzen. Filmbildende Beschichtungen können zwei Dauerhaftigkeitsgrenzen erreichen, nämlich den Wartungsintervall und den Renovierungsintervall. Bei nicht filmbildenden Beschichtungen gibt es nur eine Dauerhaftigkeitsgrenze, die eine Wartung erfordert. Die dritte Dauerhaftigkeitsgrenze bezieht sich auf das beschichtete Substrat, also den Holzteil, und ist durch den Beginn des Holzabbaues gekennzeichnet.

Due to their bio-based character, oil-based coatings become more and more prevalent in wood surface finishing. These coatings impart appealing optical and haptic properties to the wood surface, but lack sufficient protection against water and mechanical influences. The present study reports a simple green route to improve the performance of linseed oil coating by the addition of nanofibrillated cellulose (NFC). In order to achieve surface chemical compatibility with linseed oil, NFC was chemically modified with acetic anhydride and (2-dodecen-1-yl)succinic anhydride, respectively, using propylene carbonate as a solvent. NFC/linseed oil formulations were prepared and applied to wood substrates. The wear resistance of oil-coated wood surfaces was assessed by a newly developed test combining abrasive loading with subsequent contact angle measurement. As revealed by infrared and nuclear magnetic resonance (NMR) spectroscopy, as well as X-ray diffraction (XRD), NFC has been successfully modified without significantly affecting the structure of cellulose. In abrasion tests, all NFC-modified oil coatings performed better than the original oil. Interestingly, NFC only suspended in propylene carbonate, i.e., without chemical modification, had the strongest improvement effect on the coating’s wear resistance. This was primarily attributed to the loose network structure of this NFC variant which effectively prevents the oil from penetration into the wood surface, thus forming a protective NFC/oil composite layer on the wood surface.

Wood moisture content of coated panels of Scots pine sapwood was recorded during 24 months natural weathering in Vienna by logging electric resistance and temperature near the surface. Eight coating systems with various film thicknesses were used, including three solvent borne alkyd stains, three water borne acrylic stains and two water borne acrylic paints. At five sites in Europe wood moisture content of panels coated with three solvent borne alkyd stains, a brown acrylic stain and a white opaque acrylic paint was recorded weekly by changes in panel mass. Fluctuations in wood moisture content were influenced by the film thickness, water permeability and colour of the coating systems used. Degradation phenomena led to decreasing moisture protection of less durable coating systems over time of exposure. The exposure site clearly affected wood moisture content in the panels.