Scots pine (Pinus sylvestris L.) is one of the most common construction materials for general exterior applications in northern Europe. It has a wide natural geographical distribution, a good availability and it is low-priced compared to other materials. According to EN 350-2 Scots pine heartwood is considered being “untreatable” and having durability class 3. This means that its durability could and should be improved in order to deliver a more durable product with an extended and more reliable service life in outdoor applications. Reports from industry and researchers indicate that the heartwood treatability is not uniform; however, reasons for those differences remain unclear. To increase its durability by means of impregnation would be a contribution to extend the use of both a natural and native material. The aim of this study is a better understanding of the material properties with regard to impregnability. Is there a potential pattern analog to the latitudinal/longitudinal origin or other forest or wood properties such as extractive content? Understanding these factors would help to improve impregnation through better material selection. Scots pine samples from 25 different sites in six countries in northern Europe have been collected throughout autumn and winter 2009/2010. A circle of varying size containing approximately 30 trees was set up in a representative site of each stand. All diameters were measured and arranged in three classes. Three trees of each class were chosen randomly. Only the middle and upper diameter classes were used for studying heartwood permeability. The small diameter class had insufficient heartwood width to be processed. Samples of 20 x 20 x 50 mm were cut and conditioned in a climate chamber. The samples were impregnated with a water-soluble monomer furfuryl alcohol solution (FA) in two standard vacuum/pressure processes and different sealing variations. Results showed a generally low permeability but a few samples had an unexpected high ratio of filling (RoF). Further on, the samples with the highest and lowest treatability underwent an acetone extraction in an ultrasonic tabletop device. A close connection between the percentage of extractives and the treatability of the selected samples was observed. The pattern analog to latitudinal/longitudinal origin seems to exist: Samples from northern stands have lower RoF than samples from the south and those from the east have lower RoF than samples from more western stands.

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