A brief history of the situation in the Netherlands with respect to the preservation of joinery is given. Already in the eighties in the Netherlands many spruce window frames were treated with difluoride pills. One of the possible disadvantages of this kind of diffusing preservatives is the high leaching rate found in laboratory situations. The leaching rate in practice is influenced by many factors of which the condition of the paint systems and the condition of the glue in the joint are the most important. In this research the difluoride content in wood was analysed in samples which were taken from several buildings. An estimation of the remaining difluoride content leached is given. Related to these figures the remaining life of the protecting agent can be calculated. The results show that even in situations with open joints of paint damage the remaining amount of difluoride is still very high after 10 years. This suggests that in practice the leaching of difluorides is of minor importance.

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