1 INTRODUCTION

One of the factors that can be expected to significantly influence the performance of consolidants used for treating detcriorated wood is their distribution within the wood structure following treatment and removal of the solvents. In porous stone, for example, reverse migration of soluble synthetic resin consolidants can take place during the drying phase following impregnation (Domaslowski 1988). In this process, consolidant solution flows in bulk toward the surface, and the solvent evaporates there, leaving behind a high concentration of consolidant in the surface layers. Such uneven distribution of consolidant may be undesirable.

In wood, fluids can move either by bulk flow or by diffusion. Diffusion can take place by movement of vapor through the void structure or by transport of adsorbed fluid within the cell walls (Siau 1989). In drying wood from the wet state, as it is in the living tree, the major part of moisture movement takes place in the form of diffusion (Arganbright 1989). Bacterially degraded wood typically has increased permeability due to degradation of pit membranes (Blanchette et al. 1990), which would lead to increased amounts of bulk flow. Even in normal wood, bulk flow can have significant consequences, as, for instance, in the development of seasoning stain in redwood (Anderson et al. 1960). In this case water-soluble extractives are carried to the surface where the water evaporates, leaving the extractives behind, causing objectionable patterns of discoloration on the surface.

It was therefore desired to determine, by making a microscopic study of consolidant distribution, whether similar phenomena take place during solvent removal following treatment of deteriorated wood with thermoplastic synthetic resins in solution.