A wood protecting biofinish is based on a protective and decorative fungal-based coating and a linseed oil impregnation (called Xyhlo biofinish). This biofinish enables the long-term use of wood in outdoor applications without using toxic chemicals. The fire resistant properties of materials used in buildings are very important. Since Xyhlo biofinish is relatively new, only little information is available about its fire behaviour. In this study wood treated with biofinish was therefore provided with an extra treatment consisting of a halogen-free phosphate-based fire retardant to improve the fire resistance. A concerning aspect of the used fire retardant is the ability of leaching. Therefore, the leachability of the fire retardant and the effects of the biofinish on the leachability of the added fire retardant were studied. Pine wood impregnated with linseed oil and coated with biofinish provided with a phosphate-based fire retardant was tested on fire behaviour in a Single Burning Item test and a Small Flame test. Also, the effects of two types of biofinishes (biofinish A and B) on the leachability of the phosphate-based fire retardant were tested in a leachability test based on ENV 1250-2 and EN84. Results showed that wood treated with linseed oil and biofinish supplemented with a phosphate-based fire retardant meets the requirements of the European fire class B-s3, d0 (difficult inflammable). Effects of a biofinish on the leachability of the used fire retardant depends on the type of biofinish treatment. The application of biofinish B on wood impregnated with linseed oil and fire retardant diminishes leaching of the fire retardant in a watery environment. To develop a 100% leach resistant biofinish on wood that is classified as fire class B, improvements of biofinish B, the usage of non-water-soluble fire retardants and fire retardant fixation should be explored.

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