The study deals with silicon compounds, namely tetraethoxysilane (TEOS), phenyltriethoxysilane (PhTES) and methyltriethoxysilane (MTES) at concentrations of 23, 16 and 10% in combination with 1.2-1.5% boric acid. The aim with the study was to combine the chemical approach with the necessary biological tests of the impregnated wood. The tested silicon-boron combinations ensured mass loss less than 5% in a standard EN 113 test with P. placenta and T. versicolor; the combinations were also very effective against larvae of H. bajulus at all concentrations. The dynamic of MC of lap joints exposed for 19 months revealed that PhTES and MTES are highly hydrophobic, thus keeping the wood moisture content below 35% during the whole year while TEOS was found not to be hydrophobic and behaving likely untreated samples. PhTES retained very well boron while TEOS was not effective in retaining. The measured static and dynamic MOE correlated very well thus proving that both methods can be employed for testing. The both method showed some decrease in MOE depending on the tested silane and, in case of PhTES, the applied concentration.

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