Most people today use ready-prepared adhesives, partly because of their convenience, partly owing to their inherent advantages, and because in some ways they are more easily used. For instance, they are mostly employed cold so that there is no necessity to heat joints and work in a warm atmosphere as in the case of animal glue.
Resin. The most commonly used is urea-formaldehyde, a strong glue, durable, highly water resistant, and used cold. It is obtainable in various forms. One is a syrup with water-like hardener, no setting taking place until the two are in contact. Usually the syrup is applied to one part of the joint and the hardener to the other. One dis-advantage for the small user is that the syrup has a shelf life of about three months only, after which time it becomes rubbery and useless. To avoid this the adhesive is also available in powder form, needing only to be mixed with water whereupon it becomes the normal syrup. It has a shelf life of about twelve months if kept in a tight container.
Another form of resin glue is a powder in which the hardener is embodied, needing only the addition of water to convert it into glue. Resin glues can
be cured by heat, and advantage of this can sometimes be taken when a job is needed quickly or to free apparatus for other work.
P.V.A. This is a white emulsion used as supplied in the container. Certain brands have resin additives. It is used cold and has good strength though it has low water resistance.
Casein. A powder requiring the addition of water. It is used cold and has good strength, but is liable to stain certain hardwoods. It is not so widely used as formerly.
Impact. Sometimes needed for sticking plastic sheeting to wood, but is not used in general woodwork as adhesion takes place immediately the two surfaces have been brought together (after preliminary drying). Thus, the instant grab prevents joints from being fully assembled. It is occasionally useful for some awkward small veneering jobs where the use of a shaped caul would be difficult.
Animal. Obtainable in pearl or cake form, the latter needing to be broken up in sacking. It is placed in the container of a glue kettle and left overnight. The kettle is heated and the glue stirred well. The consistency is right when the brush is raised a few centimeters from the pot and the glue runs down freely without breaking up into drops yet free from lumpiness. It should never be boiled or heated directly over a flame. All parts to be glued should be heated beforehand to avoid chilling.
Epoxy resin. Of limited use for woodwork but sometimes handy for metal inlays. It is highly water resistant.
Paste. This is used only for sticking baize or leather to wood as when lining a table. Ordinary wallpaper paste with only half the normal quantity of water is used.