A round robin involving 15 European participants was set up in 2006. The round robin consisted of both a field test according to the double layer test method and a laboratory test with two different preconditioning methods. The laboratory test results were reported in an earlier IRG paper (IRG/WP13-20535) but are included also in this paper in order to facilitate the comparison with the field test results. As expected, the decay generally developed more rapidly at the southern European compared to the northern European field sites. However, the rank order of the different test groups concerning average decay ratings were the same for most field sites – Untreated pine sapwood controls had the highest decay ratings followed by TMT-UC2 (Thermally Modified Timber treated for use class 2 application), TMT-UC3, metal-free organic preservative in low retention, metal-free organic preservative in high retention, CCA in medium retention, and finally CCA in high retention that had very low decay ratings. The best compliance between field performance and laboratory test results is obtained when comparing the average results from the field tests with results from EN 113 tests with Postia placenta after natural preconditioning according to CEN/TS 15397. When evaluating the test methods it was clear that CEN/TS 15397 before the EN 113 test in laboratory seems to give far more relevant results than EN 113 after preconditioning according to EN 84 (water leaching for 2 weeks). The double layer field test does not function the way it was meant after failure ratings were reached for one or more stakes within a test group leading to collapse of the deck. This has occurred not only at the Southern European field sites but also in some cases for mid-European and Nordic test sites. After this type of collapse has been reached it is doubtful whether there is any point with continuing the test and therefore the test has now been terminated in some fields.

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