STUDIES ON IMPREGNATION PATHWAYS IN WHITE FIR (ABIES-ALBA)

Impregnation pathways in white fir wood were studied based on a capillary rise test with colored water and a vacuum-pressure impregnation with an EP resin contrasted by a fluorescent agent. Microscopic analysis confirmed that primary pathways are the longitudinal tracheids, and structures which influence dominantly all impregnation results are bordered pit pairs. Wood rays are not primarily involved in the transport of impregnation liquids, and normal heartwood is mostly impermeable. In sapwood, liquids extend preferably into the latewood zones, whereas in earlywood only isolated groups of tracheids proved to be permeable. This indicates that pit aspiration is not a homogeneous phenomenon neither within a small sample nor within one tree ring. Consequently, permeability will vary according to the extent of pit aspiration. The gradually better impregnation quality of white fir timber as compared to spruce can be explained only to a certain extent by the existence of wetwood. Additionally, one must assume that pit aspiration in fir is less. This should be used in industrial impregnation by treating fir timber with a somewhat higher pressure to improve impregnation depth, compared to spruce. Because of the more permeable capillary system, danger of wood collapse is limited. No reliable and quick method has been found to predict the treatability of white fir prior to the treating process.