Thin radial/longitudinal sections (~100 µ) of Scots Pine (Pinus sylvestris) and lime (Tilia vulgaris), were exposed to deionised water over the temperature range 25-65°C. Losses in wet tensile strength and toughness occurred rapidly at temperatures from about 50°C upwards. After about 2 months' exposure pine lost some 10-30% of its tensile strength and 20-60% of its toughness. For lime the losses were somewhat greater, being about 20-60% for tensile strength and up to about 80% for toughness. Further prolonged exposure for about 18 months led to about 60% tensile strength loss in pine and 80% in lime. For both species some 90% loss in toughness occurred after this period of exposure. Dry tested specimens and those tested wet but at "zero span" retained a much higher proportion of their original strength. These specimens failed mainly by simple intra-fibre fracture, whereas the lime specimens tested wet at finite span, showed marked inter-fibre shear failure. No such clear cut distinction in failure mode could be observed with pine, although in this species also, scanning electron micrography showed marked degradation in the middle lamella region. It is believed that the phenomena reported are due purely to physicochemical processes and that they may contribute significantly to detachment of paints and other finishes from wood surfaces.

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