In 2005 an extensive test program including field tests was set up in order to obtain more data on the durability and long term performance of modified wood and semi-durable wood species. One of the main challenges for modified wood is to predict accurate service life time in UC3 (use class 3, above ground) and UC4 (use class 4, in soil or fresh water contact). So far, data from in-service conditions are rare, while several studies have evaluated the durability in lab or field test exposure. However, there is still a lack of studies comparing replicate modified wood products in both field and lab exposure. This study evaluates the efficacy of modified wood in AWPA E10, three different types of soil in laboratory (ENV 807), three test fields in-ground (EN 252) and two close to ground (horizontal double layer test – HDL) set-ups at two test sites. The test material includes furfurylated, acetylated and thermally modified wood in addition to reference treated and control samples. In laboratory, furfurylated, acetylated and thermally modified pine (212ºC) performed well. The modified wood samples performed at the same level, or better, than the reference CC and CCA preservatives in retentions for UC4 applications. In the horizontal double layer test, five years is still too short time to be able to draw firm conclusions. However, in the most accelerated HDL set-up, all controls have failed or are moderately to severely decayed whereas most preservative treated, furfurylated and acetylated wood are sound or only slightly decayed. After 5 years of testing CCA-preserved wood performs better in-ground in field tests than in lab tests, whereas modified wood generally performs slightly poorer in the field tests. Both in lab and field tests, acetylated wood performs equal to CCA-preserved wood in UC4. Furfurylated wood performs equal to or better than UC3 level preservative treated wood. Thermally modified wood actually performs much poorer than all preservative treated wood references. Finally, natural durability classification of the same treatment in different lab and field tests was rather similar.

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