TECHNICAL NOTE number 256 
 
 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE 
 
 FOREST PRODUCTS LABORATORY 
 
 madison 5. Wisconsin February 1953 
 
 HOW TO SELECT A WOODWORKING GLUE 
 
 The variety of types and trade -name brands of glues available to the 
 woodworker often makes selection of the proper glue appear difficult. 
 This choice may be simplified, however, by answering the following 
 four questions with reference to the particular job in mind. It is the 
 purpose of this short discussion to merely raise the questions. The glue 
 user may answer these for his own application by reference to past ex- 
 perience, to literature supplied by the glue manufacturers, and to re- 
 ports of the Forest Products Laboratory (See Technical Notes Nos. 257 
 and 258). 
 
 (1) What sort of glued joint is involved ? The answer to this question 
 requires consideration of the design of the joint, its dimensions, and 
 sometimes the species of wood used. Certain plywood and flat grain- 
 to-flat grain laminated joints are relatively easy to glue with a variety 
 of glues; other types of joints, such as a butt joint of two end-grain sur- 
 faces, may be very difficult or almost impossible to glue satisfactorily 
 with any glue. Some glues, such as soybean glues, are particularly 
 suitable for gluing softwood veneers, some for assembly work with dowels 
 or dovetail joints, and some for heavy laminated constructions. Certain 
 glues may be used in a variety of constructions and types of joints. 
 
 (2) What facilities will be available for the gluing operation ? Or, what 
 working properties will be required of the glue ? Nearly all glues are 
 suitable for industrial use if plants are provided with the necessary 
 equipment, but equipment requirements vary considerably for the differ- 
 ent types of glues. The choice of glues for small-scale operations or 
 hobby work is likely to be more restricted than for large-scale opera- 
 tions because of the limited equipment available. For some glues, equip- 
 ment is required for heating the joints at elevated temperatures in order 
 to develop proper strength, although others may be pressed at normal 
 room temperatures. Consideration must also be given to the equipment 
 needs for measuring out ingredients, mixing glues, spreading glue, and 
 
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 applying and maintaining pressure on the .,_-— xemperature require- 
 ments for the shop, wood, and glue, the length of time required between 
 spreading and application of pressure (assembly period), and the length 
 of time that the joint must be under pressure are important in choosing 
 a glue. The user will also wish to consider the length of time that any 
 glue remains usable (the working life or pot life) once it is prepared for 
 use, as well as the length of time that the glue components may be safely 
 stored before being prepared for use (the shelf life or storage life). 
 Glues also differ in the ease with which they can be cleaned from equip- 
 ment after use. 
 
 (3) How durable should the glued joint be ? When properly used, most 
 currently available glues are capable of giving high original dry-joint 
 strength and of remaining durable under dry, normal temperature con- 
 ditions. However, the resistance of the joints to deterioration in serv- 
 ice varies widely with different glues. In fact, the improved resistance 
 to deterioration of the newer resin glues is a principal reason for their 
 development and increasing use. Generally, different brands of the same 
 chemical type of glue will have similar durability characteristics. Dur- 
 ability of glues thus varies from the relatively low moisture resistance 
 of animal and vegetable glues to the high all-around durability of the 
 phenol-, resorcinol-, and melamine-resin glues, which when properly 
 used give joints that are as durable as untreated wood itself under severe 
 exposure. 
 
 (4) How important is cost? Since prices of glues are continually chang- 
 ing and often depend largely on the quantities ordered, it is impractical 
 to»list exact figures. Costs increase, however, from the relatively low- 
 cost soybean and vegetable glues to the animal, casein, urea-resin, and 
 phenol-resin glues, to the melamine-resin glues, and finally to the re- 
 sorcinol-resin glues, which are most expensive on the pound basis. Cost 
 must be considered, however, in terms of the actual cost per pound of 
 mixed glue, rather than the cost of ingredients as received, and of the 
 amount of glue spread required; that is, the cost to spread a certain 
 area of surface mustbe considered. Wastage due to short pot life, costs 
 of rejected material due to lack of control of the gluing process, and 
 costs of the equipment and manpower needed for commercial processes 
 must also be weighed in comparing glue costs. 
 
 ZM 92361 F Agr iculture-Mad Isor