Knot staining resistance of wood coatings
Odpornost premazov proti obarvanju zaradi grč v lesu
Keywords:wood, knot, coating, staining
After wood has been coated and exposed to external climatic conditions and/or elevated temperatures,
staining of the coating film by hydrophilic and lipophilic extractives may occur where knots are located. For this reason, the knot staining resistance of the coating system is very important. In our study, we tested some basic types of white pigmented systems. In doing so, we adapted the method SIST EN 927-7:2020 according to our capabilities, optimized it and critically evaluated whether there is room for improvement of the standardized method. The results of our research showed that the knot staining resistance of coating systems is related to the type of solvent in the coatings, the hiding power of the system and its build-up or dry film thickness. Accordingly, solvent-borne coatings were found to be better, as were those containing more pigments and those with a higher dry film thickness. We have also found that by evaluating the colour difference on the regions with and without knots before exposure and accounting for this in evaluation of colour differences after exposure, we can make a much more objective classification of coating systems according to their effectiveness against knot staining. Based on this finding, we believe that the standardized method needs to be corrected accordingly.
Ahola, P., Derbyshire, H., Hora, G., & De Meijer, M. (1999). Water protection of wooden window joinery painted with low organic solvent paints with known composition. Part 1. Results of inter-laboratory tests. Holz als Roh- und Werklstoff, 57, 45–50. DOI: https://doi.org/10.1007/PL00002620
Buchelt, B., & Wagenführ, A. (2012). Evaluation of color differences on wood surfaces. European Journal of Wood and Wood Products, 70 (1-3), 389–39. DOI: https://doi.org/10.1007/s00107-011-0545-z
De Meijer, M. (1999). Interactions between wood and coatings with low organic solvent content. PhD thesis, Wageningen University, Wageningen.
De Meijer, M. (2000). Comparison between laboratory water permeability test and wood moisture content in full scale window frames. V: Second Woodcoatings Congress. Woodcoatings. Challenges and Solutions in the 21st Century. October 2000 Hague, Netherlands, Congress papers. Hague; Teddington: Paint research association, 23–25.
Derbyshire, H., & Miller, E. R. (1996). Moisture conditions in coated exterior wood. Part 1: An investigation on the moisture transmission characteristics of exterior wood coatings and the effect of weathering on coating permeability. Journal of the Institute of Wood Science, 14 (1), 40–47.
Ekstedt, J. (2002). Studies on the barrier properties of exterior wood coatings. PhD thesis. Stockholm, KTH- Royal Institute of Technology, Department of Civil and Architectural Engineering, Division of Building Materials.
Ekstedt, J., & Östberg, G. (2001). Liquid Water Permeability of Exterior Wood Coatings – Testing According to a Proposed European Standard Method. Journal of Coating Technology, 73 (914), 53–59. DOI: https://doi.org/10.1007/BF02698438
Golob, V., & Golob, D. (2001). Teorija barvne metrike. V: Interdisciplinarnost barve. 1. del. V znanosti, Maribor, 2001. Jeler, S., Kumar, M. (ur.). Ljubljana, Tiskarna Pleško, 199–230.
Kimerling, A. S., & Bhatia, S. R. (2004). Block copolymers as low-VOC coatings for wood: characterization and tannin bleed resistance. Progress in Organic Coatings, 51, 15–26. DOI: https://doi.org/10.1016/j.porgcoat.2004.03.006
Mihevc, V., Knehtl, B., & Žepič, R. (1995). Water-vapour permeability of the wood-coating system of different surface coating systems. Zbornik gozdarstva in lesarstva, 46, 177–190.
Nussbaum, R. N. (2004). The effect of processing and treatment parameters on the discoloration of painted joinery due to resin exudation from knots. Surface Coatings International Part B: Coatings Transactions, 87, 4, 181–186. DOI: https://doi.org/10.1007/BF02699633
Osram (2021). Ultra vitalux 300 W 230 V E27: Data sheet. https://www.osram.com/ecat/ULTRA-VITALU UV-A-UV-A-Ultraviolet lamps-Industry-Specialty Lighting/com/en/GPS01_1028569/ZMP_60829/ (27. 7. 2021).
Pavlič, M. (2009). Lastnosti površinskih premazov v odvisnosti od njihovih interakcij s termično modificiranim lesom. Doktorska disertacija. Ljubljana, Univerza v Ljubljani, Biotehniška fakulteta, 3–59.
SIST EN 927-7 (2020). Barve in laki - Premazi in premazni sistemi za zaščito lesa za zunanjo uporabo - 7. del: Ocenjevanje odpornosti premazov proti obarvanju zaradi grč v lesu. Paints and varnishes - Coating materials and coating systems for exterior wood - Part 7: Assessment of knot staining resistance of wood coatings (EN 927-7: 2020).
SIST EN ISO 11507 (2007). Barve in laki - Izpostavitev premazov umetnemu vremenskemu staranju - Izpostavitev fluorescentnemu UV sevanju in vodi. Paints and varnishes - Exposure of coatings to artificial weathering - Exposure to fluorescent UV lamps and water (EN ISO 11507: 2007).
SIST EN ISO 2808 (2019). Barve in laki - Ugotavljanje debeline plasti (ISO 2808:2019). Paints and varnishes - Determination of film thickness (ISO 2808: 2019).
SIST-TS CEN/TS 16359 (2012). Barve in laki - Premazi in premazni sistemi za zaščito lesa v zunanji uporabi - Ocenjevanje odpornosti premazov proti obarvanju zaradi lesnih grč. Paints and varnishes - Coating materials and coating systems for exterior wood - Assessment of knot staining resistance of wood coatings (CEN/TS 16359: 2012).
Suttie, E., & Ekstedt, J. (2004). Evaluation of a method to determine discoloration of paints on wood due to tannin staining from knots. Surface Coatings International Part B: Coatings Transactions, 87 (1), 57–61. DOI: https://doi.org/10.1007/BF02699566
Van der Wel, G. K., & Adan, O. C. G. (1999). Moisture in organic coatings – a review. Progress in Organic Coatings, 37, 1–14. DOI: https://doi.org/10.1016/S0300-9440(99)00058-2
Vrbec, J. (2021). Optimizacija metode določanja odpornosti premazov proti obarvanju zaradi grč v lesu. Diplomsko delo. Ljubljana, Univerza v Ljubljani, Biotehniška fakulteta: 8–13.
Wegen, W. H., & Hellwig, V. 2000. Artificial weathering of coatings including blue stain infection under laboratory conditions. V: Second Woodcoatings Congress. Woodcoatings. Challenges and Solutions in the 21st Century. October 2000 Hague, Netherlands, Congress papers. Hague; Teddington: Paint research association, 23–25.
Williams, R. S., Jourdain, C., Daisey, G. I., & Springate, R. W. (2000). Wood Properties Affecting Finish Service Life. Journal of Coatings Technology, 72 (902) 35–42. DOI: https://doi.org/10.1007/BF02698003
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Copyright (c) 2021 Matjaž Pavlič, Jure Vrbec, Jure Žigon, Marko Petrič
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