Creosote gives the best protection against decay for sleepers and poles. However, it has a major drawback - bleeding. Modified impregnation processes to reduce bleeding have been tried. For developing such processes it is important to know the actual temperature and pressure inside the wood. This paper describes measurement of temperature and pressure inside wood during creosote impregnation. The experiments have been performed at a research plant using poles of Scots pine (Pinus sylvestris L.). Boiling under vacuum before impregnation increased the temperature inside the sapwood to 80-90°C within 1½ hours. The pre-pressure of the Rueping process applied in the vessel raised the pressure inside the sapwood immediately to the same level as in the vessel. When the oil-pressure was applied the pressure inside the wood rose more slowly and generally did not reach the level in the vessel. During the final vacuum there was still pressure above atmospheric inside the wood in most of the experiment charges.

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