The diffusibility of Boron in wood and thus its leaching behaviour in water contact is known since long. Nevertheless quantitative data on the long-term leaching behaviour are rare. Consequently, field exposure tests were started with beam-segments treated with pure boric acid and with poles treated with CCB. Detailed data of more than five years of field exposure are now available. Pure boron treated pine beams exposed to Northern German climate show severe leaching from the outer centimetre. Chemical analysis reveals a still even and effective distribution over the entire cross section including heartwood but with prolonged exposure it can be assumed that the protection level would have been lost. The surface coat showed high effectiveness in the first month but did not prevent severe leaching in extended exposure. After five years now significant differences between coated and uncoated samples could be observed. CCB treated poles out of ground contact lost under the same conditions about 35% of Boron, 2% of Copper and 0, 1% of Chromium.

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