Changes in constituents, adhesive bond, and correlation between the thickness swelling, internal bond, compression shear strength of particleboards, MDF boards, OSB and plywood shear strength were studied. The thickness swelling was determined by exposure to a high humidity and dry and by immersion in water. Prior to and after mentioned exposures, we had determined the tensile shear strength, internal bond, shear strength and thickness swelling. The results have shown that while in normal state, particleboards have the best compression shear strength, whereas OSB showed lowest values. When exposed to humidity, particleboards had the highest values, while MDF the lowest. At immersion, the highest values were determined at OSB and the lowest at MDF. We have also performed an SEM analysis with where we confirmed changes in and between constituents (stresses in glue line) as well as constituents failures.