This paper reports on the effect that organosilicon compounds and potassium carbonate and urea (PCU) have on wood flammability. The study focus on reducing wood flammability by promoting char formation through manipulation of the condensed phase decomposition chemistry. Potassium carbonate is known as an effective fire retardant, however it is easily leached out from wood and increases its hygroscopicity. The aim of the research was to assess the ability of selected organosilicon compounds to reduce potassium carbonate leachability from the treated wood. The study was performed through the mini fire tube (MFT) method, where fireproofing properties of the treated wood were evaluated. Pine sapwood treated with PCU at the retention of ca. 160kg/m3 showed 6% of wood mass loss as a result of combustion in MFT. The fireproofness effect has been reduced due to the ageing procedure and displayed 60% of wood mass loss. It has been shown that some selected silanes or their blends with siloxanes, superficialy applied on treated wood, allowed to retain PCU in wood and maintain its fireproofness. Wood mass loss resulting from sample’s combustion was significantly reduced (ML<10%). AEAPTMOS, VTMOS and a mixture of alkylalkoxysilanes turned out to be most effective agents limiting potassium carbonate leachability and maintaining wood fireproofness.

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