Several test methods are used to determine the efficiency of water repellent treatments on wood. The most common are: contact angle measurement, swelling rate of samples immersed under water and, the increase in mass of wood samples with time or after a fixed period of time either fully immersed under, or partially immersed in or floating on water. In this paper, some fundamental aspects of the latter, gravimetric method are discussed. Several wood species were tested in a water soak test and their mass increase was recorded after 24 hours. The influence of depth of immersion and factors such as axial sealing and water repellent treatment were included as variables. It was tested whether an increase in pressure occurred inside wood samples during complete immersion under water. Water uptake at different depths was found to be wood species depending. Increased pressure inside Pinus sylvestris samples completely immersed under water was observed. This could be attributed to compression of air resulting from the penetration of water during complete immersion.

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