One is adhesion - the molecular force which makes the glue stick to the wood. For many years, it was assumed that the adhesive formed tiny hardened tendrils within the porous structure of the wood which interlocked the two pieces of wood together, much like hundreds of tiny mortise and tenon joints. This mechanical adhesion does play a small part in the glue joint, but current scientific opinion is that a different type of force called specific adhesion, is much more important. Specific adhesion results from strong molecular attraction between the wood and the glue and for this to occur, the adhesive must penetrate the wood cells and "wet" the fibres.

Second force involved in a glue joint is cohesion - the force that makes the glue stick to itself. This is the solid glue "line" in a joint. It is the strongest when the two pieces to be joined are machined so they mate as closely as possible. This results in a glue line that may only be a few thousandths of an inch thick.

Glues cure in two general ways. One is by evaporation of a solvent that results in hardened glue molecules formed within the structure of the wood. White glues, yellow glues, and animal hide glues cure in this way.

Other glues, like two-part epoxy, urea-formaldehyde and super glues cure when a chemical reaction takes place and the glue molecules undergo a chemical transformation called polymerization, resulting in a hard, rigid structure of more complex molecules. As a rule, these glues are more waterproof than the evaporative glues.

Some newer glues like Maxibond and Liquid Nails are weatherproof glues that cure by both evaporation of solvent and subsequent polymerization of the molecules. This two part process give these glues improved water-resistance and are generally more economical than the epoxies and the plastic resin glues.