Migration of extractives to the wood surface alters the properties of wood as an adherent. Extractives change the wettability and the curing properties of adhesives. A desirable wettability-permeability relationship is sometimes affected by extractives, thus reducing the gluebond strength and performance. Past efforts to determine which of the components of extractives affect adhesion are reviewed. The most common deleterious effect of extractives on finishing is discoloration of coatings and paint films. Another adverse effect is that extractives retard the hardening of finishes. Not all the effects are unfavorable, however. Some extractives significantly improve the durability of the surface-coating and contribute to paint holding. Methods of minimizing the effects of extractives are also reviewed. Their application depends on the wood species involved and on the relative value of the products. Economic principles dictate the feasibility of the methods used.
Hse, Chung-Yun; Kuo, Mon-Lin. 1988. Influence of extractives on wood gluing and finishing- a review. Forest Products Journal 38(1):52-56