Testing durability of treated wood according to EN 252 – Interpretation of data from Nordic test fields (NT TR 591)

  • Report #: NT TR 591
  • Approved: March 2006
  • Author(s): Marie-Louise Edlund, Fred Evans, Keld Henriksen
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  To evaluate the effectiveness of new wood preservatives intended for treated wood in ground use there is an European standard, EN 252. The test shall run for five years before any interpretation of the results can be made. Due to environmental concerns, the use of wood preservatives based on copper, chromium and arsenic (CCA) has been restricted in recent years. As a consequence of restrictions, several chromium and arsenic free preservatives based on fungicides regarded as more environmentally acceptable have been registered for use in the Nordic countries. Experience from our field tests shows that some preservatives perform quite well in field tests during the first five years but fail during the next five year period, while other perform quite good even during longer time in field. The aim with the study was to find early signs to predict preservatives service life by using other evaluation procedures than those described in EN 252. The aim has not been reached. To find the early signs of failure the field test according to EN 252 must be coordinated with other relevant methods to overlap weaknesses in EN 252. Some changes of the standard could give a better understanding of the performance of the tested wood:
  • Additional stakes must be treated to analyse the penetrating properties of the preservatives.
  • The test must be carried out in more than one field with different dominating wood destroying micro-organisms. The quality of the fields must be declared. Preferably the stakes shall be exposed to all kinds of wood destroying micro-organisms.
  • Test reports must include both index of decay with standard deviation and number of attacked stakes with different grading for the whole test period.
  • Testing according to EN 252 must be combined with other relevant test methods.
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