The major defining characteristic of lumber cut from trees that have been infected with the mountain pine beetle is the extent of fungal bluestain in the sapwood. It is reported that bluestained wood has shown increased permeability, and questions arose as to whether the application of an adhesive or a finish coating may be adversely affected. Laminating of wood is a key value-added process and one that is very dependent on the quality of the bond between two or more components. Bluestain is a common phenomenon in the secondary wood processing industry where finishing is part of the value-adding process. The finishing evaluations made in this study were intended to benefit these processors.
Pieces of bluestained and non-stained 2 x 4 in. lodgepole pine lumber were dried to a moisture content typically targeted by the furniture sector — i.e., much drier than lumber used for structural purposes. From this lumber, specially constructed edge-glued panels were made which exhibited bluestained to bluestained joints and non-stained to non-stained joints. This construction method provides bluestained and non-stained joints for the laminating tests, as well as providing a good representation of what will really happen in an industrial setting where bluestain most likely will not be separated from non-stain. Each panel was cut in half, with one half being used for the laminating tests and the other half for the finishing evaluations. The strength and durability of the glue lines were measured. Various finish coatings either used alone or in combinations with others were subjectively evaluated.
The laminating tests show that gluelines in lodgepole pine that contains beetle-transmitted bluestain were not significantly different in strength from gluelines in unstained wood when PVA and PRF adhesives are used. The durability of the bluestained beetle-killed wood gluelines easily met the requirements specified by the ASTM D1101 standard.
Where desired, the appearance of bluestained wood can be enhanced or highlighted by a simple standard clear furniture finish. Bluestain in parts of edge-glued panels can be masked if certain types of finishes are employed. The finishes that gave more consistently good masking results were those containing blue, red, and charcoal tints in the stain, toner, or glaze coatings. Increased permeability of the bluestain did not affect the adherence of any of the finishes.
While the finishing evaluations indicate the possibilities for finishing pine, whether it has bluestain or not, market research is recommended, using the best performing finishes on full-scale furniture pieces, to test consumer acceptance.