At most every stage of woodwork construction, there is a need for quality gluing. During the early stages of construction, it may be required to glue several narrow pieces to form a wide panel, as in the case of a table top. In the later stages, it may be necessary to glue subassemblies. Gluing also allows you to use many pieces and parts of boards that would otherwise be scrap. All in all, proper gluing is a must. Also, special gluing operations, such as laminating, veneering, overlaying and marquetry, are important to different segments of the forest products industry, but they will not be discussed in detail in this publication.
During the planning stages, the woodworker decides what pieces are needed and which pieces will need to be glued together. The proper selection of adhesive and its curing process can save alot of headaches, as well as reduce the amount of time the woodworker must be away from other jobs.
So, what needs to be considered when two pieces are to be glued? The first consideration is what type of glue, or adhesive, will be used. An adhesive is a substance capable of holding other materials together by surface attraction. Today, the use of all adhesives is collectively grouped as “gluing.” The decision of which adhesive to use depends on a number of things. Different jobs require different adhesives, so let’s look at some factors which influence the adhesion process.
Since wood is porous, and different woods have different properties, wood is not an easy material to glue. Because of wood’s porosity, it can absorb liquid. Most glues used in the woodworking industry are liquid. Although some are water-based, others are not. Couple this with different ways to glue wood, and the complexities of gluing increase again. Because the properties of wood vary across one piece of wood, the adhesive is absorbed more in one direction than in the other two directions. The absorption of the adhesive is lowest on the edge grain and highest on the end grain. Absorption on the face is somewhere between the edge and end grains. Given these different absorption levels in wood, the simplest method of gluing is to glue two pieces edge to edge. Face-to-face gluing is more difficult, and gluing end grain to end grain is probably the most complicated because the end grain of wood absorbs so much adhesive.
Todd Shupe is the President of Wood Science Consulting, LLC. He is a a well-recognized expert on wood preservation, insects and fungi, wood decay and degradation, and wood species identification. He has a broad background in new product development, quality management, and marketing and sales in both the public and private sectors. For more information please visit DrToddShupe.com.