Conventional methods of impregnation have to be improved for achieving better penetration of refractory wood species. Basic requirements for an adjustment of treatment schedules are, amoung others, a profound knowledge of the course of pressure changes in the wood during treatment. A new method of pressure measurement was developed which supplies exact and reproducible data. The results show that air pressure spreads more rapidly in wood than water pressure. In pine, water pressure is built up in radial direction within hours an declines slowly after pressure release. In spruce, air and water pressure spread more rapidly in green wood than in dry wood. Water pressure of 5 bar applied in radial direction is not achieved within 8 hours time. 5 minutes successions of pressure and pressure release have no effects at 10 mm depth. These findings call into question the conventional OPM technique of rapid successions of pressure and vacuum, and possibly allow easier treating techniques.

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