The use of wood is increasing for both ecological reasons and because of greater knowledge of its proper use. The untreated naturally grayed appearance of the wood is interesting. Since the aging processes are different depending on the method of protection, method of installation, the place of installation, the orientation of the sides, etc., we have developed a preparation that removes or greatly reduces those effects and unifies the appearance of wood in all places and methods of installation. The basic solution was composed of demineralized water and iron (II) sulfate (FeSO4). Boric acid (Ba) and quaternary ammonium compounds (QUAT), which are used for biocidal protection, were added in various combinations and concentrations. The preparations were tested on larch (Larix decidua Mill.) and spruce (Picea abies Karst.) wood. We used larch wood only for external exposure. Then we immersed the samples in various combinations of solutions for ten minutes before testing. Half of them were than exposed to UV. We also did a test of resistance to decaying fungi. We measured an average weight loss of 17.16 % in untreated samples. The best wood protection was achieved with 5 % FeSO4 + 0.2 % Ba + 0.2 % QUAT. In addition, this preparation performed its best in short-term immersion, long-term immersion and exposure at 100 % humidity. The average iron content was about 990 ppm after treatment and measured on XRF, and it almost halved after the first week. After 9 months the final content was somewhere around 80 ppm. Iron sulfate reacts with wood, and in a few days the samples gain a gray patina similar to natural aging. After one week, treated samples are already darker than untreated samples after 9 months.
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