This study analyses the work of adhesion calculated according to the Young-Dupre equation and the work of adhesion calculated based on the interactions at the interface between the coating material in the liquid phase and the wood. It has been shown that the adhesion of coating materials to wood and their ability to spread over the substrate surface are primarily controlled by interactions between the surface forces at the interface. The values of these interactions confirmed that the tested materials should spread spontaneously over the wood surface. There are also discussed the secondary factors that can significantly influence the interactions between the surface forces and, consequently, the final stability of the examined system. The values of surface free energy for the hardened coating materials were considerably higher than the original values of surface free energy for the corresponding liquid coatings - especially due to the several times higher polar component. We also observed a considerable increase of the work of adhesion of the coating materials to the wood due to the hardening process. This increase resulted mainly from interactions between the polar components of surface free energy of the adjacent phases. The increase in adhesion of the coating materials during the hardening process was accompanied by a decrease in the interfacial free energy at the interface with the substrate. Mechanical testing of the stability of the coating material-wood system showed that the failure in the system always occurred in accordance with the calculated values of the work of adhesion of the coating material to the wood and the work of cohesion of the coating material and of the wood substrate.