The purpose of this thesis was to determine and compare the fungicidal properties of a newer biocide based on quaternary ammonium compounds, polymeric betaine, with an existing, commercially known preparation, alkyl dimethyl benzyl ammonium chloride (ADBAC). The efficacy against brown rot (Gloeophyllum trabeum) and white rot (Trametes versicolor) fungi was determined according to the SIST EN 113 (1995) standard. In the test, we used samples of beech (Fagus sylvatica) and pine (Pinus sylvestris), which were vacuum-pressure impregnated with aqueous solutions of both biocides at mass concentrations of 0.1%, 0.25%, and 0.5%. Half of the test specimens were subjected to artificial aging by leaching according to the SIST EN 84 (1996) standard, which simulated washing out by rain. Additionally, we tested the effectiveness of polymeric betaine as a coating agent against blue-stain fungi according to the SIST EN 152-1 (1996) standard and during a 4-month exposure to external conditions. It was found that the efficacy of both preparations is strongly linked to the concentration used. At concentrations of 0.1% and 0.25%, the protection was insufficient, while at 0.5%, both biocides achieved comparable efficacy with a mass loss below 5%. Although leaching reduced the efficacy, the minor differences suggest, that the fixation into the wood itself is effective. The surface application of polymeric betaine was noticeably more effective against blue-stain fungi at 0.25% and 0.5%, but it did not completely prevent staining. As a standalone surface coating, it was not effective under outdoor conditions, as no difference was observed between the protected and control samples.
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