Exterior wood is exposed to various environmental factors that cause weathering. Weathering is important primarily from an aesthetic standpoint. However, not all parts of the building are equally susceptible to weathering. Parts exposed to moisture will discolour faster than protected parts, such as wood under roof overhangs. To achieve fast and uniform artificial greying, a surface treatment with iron(II) sulphate can be used, similar to natural greying. In this study, we investigated the influence of boric acid and quarterly ammonium in combination with a solution based on an iron (II)sulphate-based solution. We treated spruce samples with different concentrations of iron(II)sulphate and biocides. After treatment, decay and water performance tests were conducted. From the test results, the wettability factor kwa and the inherent resistance factor kinh were determined. Both factors were used to calculate the resistance dose (DRd) according to the Meyer-Veltrup model. The samples were also exposed outdoors. During exposure, colour changes and iron leaching were monitored. The results show that the addition of biocides has no effect on the rate of colour change and the final colour. However, it should be noted that after only one week of exposure, 40% of the iron had leached from the surface. The addition of biocides has a positive effect on the durability of the treated wood, regardless of the low retention of the preservative solutions.

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