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The impregnation process of Scots pine and beech samples with tannin solutions was investigated. The two materials involved in the process (impregnation solution and wood samples) are studied in depth. Viscosity of mimosa tannin solutions and the anatomical aspect of beech and Scots pine were analysed and correlated. The viscosity of tannin solutions presents a non-newtonian behaviour when its pH level increases, and in the case of addition of hexamine as a hardener, the crosslinking of the flavonoids turns out to be of great importance. During the impregnation of Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.), the liquid and solid uptakes were monitored while taking into consideration the different conditions of the impregnation process. This method allowed to identify the best conditions needed in order to get a successful preservative uptake for each wooden substrate. The penetration mechanism within the wood of both species was revealed with the aid of a microscopic analysis. Scots pine is impregnated through the tracheids in the longitudinal direction and through parenchyma rays in the radial direction, whereas in beech, the penetration occurs almost completely through longitudinal vessels.

The easy leaching of boron from wood preservation formulations has limited the use of this highly active fungicide. The recently discovered adduct with flavonoids allows boron to be retained for longer periods of time within wood and consequently to extend its life. Two different leaching treatments were compared, and the fungal and termite decay were examined. The biological tests showed extremely high resistance of the leached samples against both fungus (Coriolus Versicolor and Coniophora Puteana) and termites (Reticulitermes Santonensis). The retention of 2.5 kg/m³ was determined as the threshold of efficacy of boron in flavonoid-based wood preservative. Furthermore, solid state 13C-NMR analysis of the tannin resin indicated that boron can be covalently fixed to the tannin-hexamine network.