Prior to World War II, there were three types of woodworking adhesives in widespread use: animal or hide glues (number one), blood glues (waterproof) and casein (milk-based) adhesives. The increased need for more versatile and more durable adhesives for laminated beams, plywood and other composite products resulted in the development and use of adhesives derived from petrochemicals. Today, we have at least seven major types of woodworking adhesives, and within each type there are numerous brands and variations in properties both working properties and final glue-joint properties.
A note about vocabulary.
Past generations used the word "glue" to refer just to the adhesive made from animal hides and other animal parts, in other words, animal glue. Adhesives referred to all the others, especially those based on petrochemicals. Today, however, common usage trends permit us to term all woodworking adhesives as glues. In fact, have you ever heard a glue-joint called an adhesive-joint? Can you image "Super-Glue" called "Super-Adhesive" instead? But technically, especially for us old-timers, we prefer to use the word adhesive whenever possible, rather than glue. Perhaps it is a privilege of old age?
When choosing an adhesive (see Adhesive properties sidebar on page 22), you first need to determine the properties you need. Remember that for better adhesives, you will pay more; yet the cost of an adhesive is small compared to the cost of the product made or compared to the cost of repairing a glue-joint. Key properties would include:
How much time can be tolerated between the application of the glue and putting the two pieces of wood together with the required pressure? Sometimes, this is called assembly time or open time.
Can the pieces of wood be moved slightly after they are put together without loss of joint integrity or is no adjustment possible?
How fast does the adhesive cure and establish 50 percent or greater joint strength?
How will the adhesive perform as the wood temperature at the time of application varies from wintertime (65 F) to summertime (80 F)?
Can the adhesive bridge any gaps (usually we consider a space greater than 0.006 inch or 1/128 inch to be a gap between the two pieces of wood) and still maintain high strength?
Will the adhesive stain the wood?
Will the finishing system or other processing affect the adhesive?
Will squeeze-out residue affect finishing?
Once opened, will the adhesive in the can, bottle or tube age rapidly?
Is the adhesive waterproof or water-resistant (not quite as good as water-proof)?
How will heat affect the glue-joint?
Note that the strength of the joint for furniture and cabinets is not an issue, as every woodworking adhesive, if properly used, will develop a joint that is stronger than the wood itself, except for animal glues.
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