Quality of impregnated timber is most often expressed by penetration and retention of the preservative used. Relatively less information is available about the performance of the final product, e.g. decks, panels etc. regarding product’s surface checks, deformations and overall appearance. Together with the timber durability, the above mention features are of esthetical importance in the above ground performance of timber. A comprehensive Nordic project dealing with pre-treatment, impregnation, durability and performance of Scots pine timber impregnated with copper-based preservatives for above ground use (class AB) was recently finished. The results from an above ground trail concerning the quality of timber are presented. The timber was dried in a conventional progressive, batch and high temperature kiln prior to impregnation. A significantly better quality regarding checks, deformations and deviation of the final moisture content, was achieved after conventional batch and high temperature dryings. Three preservatives (Kemwood ACQ 1900, Tanalith E and Wolmanit CX-8) were impregnated. The high temperature drying ensured the best penetration of all preservatives, but the retention was lower compared to conventional progressive and batch kiln dried timber. A part of the planks were conventionally kiln dried after the impregnation, the second part was air dried. Two decks with planks covering the variations in primary drying and preservative used were exposed; the former deck was in the open, the later one was under a shelter. After three years in service the planks were assessed regarding checks, deformations and moisture content. All three preservatives showed satisfactory appearance and no indication of decay was found. The deformations were comparable to those measured directly after final drying; the type of exposure had effect on the checks and moisture content of timber.

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