For the experimental assessment of the diffusion of boric acid and difluorides over a three year period 2 tests were set up. In a test with large spruce blocks (150 x 150 x 300 mm³) 3 different pill types were exposed to 3 different climates: climate room (20°C, 65% r.h.), wet room (20°C, 95% r.h.), and to outside exposure. In a test with open L-joints without paint, with an alkyd paint and with an acrylic paint the same pill types were exposed outside, to the Dutch weather. From both tests it was concluded that the diffusion of difluorides is good under all circumstances and that differences in m.c. did not influence the diffusion to a large extent. The boric acid diffusion rate is much slower and very dependent upon m.c. In unglued samples with alkyd paint the highest m.c.'s were reached and thus the best diffusion.

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