How to choose Wood glue?

animal glue

For many centuries, animal glue, especially raw hide glue, has been the main adhesive of choice for many types of woodworking (including furniture and shoe factories). It is made of collagen extracted from animal skin (hidden). Its chemical properties are similar to edible gelatin, and if ingested, it is non-toxic. Nowadays, animal hide glue is still used in special applications: musical instruments (truth factory), replica furniture, and protection grade restoration of antique wood products. The measurement of rawhide glue is based on its gel strength, which is a measure of the number of gram required to press a 1⁄2 inch (13 mm) plunger 4 mm (0.16 inch) into the glue's 12.5% ​​protein solution. 10°C (50°F). The standard grade of glue is 32–512 grams (1.1–18.1 ounces). The strength of 192 grams (6.8 ounces) is the most commonly used strength for woodworking. 251 grams (8.9 ounces) is the highest content commonly used in instrument manufacturing; 135 grams (4.8 ounces) is the lowest material used in ordinary wood products. Glue with a strength of more than 250 grams (8.8 ounces) needs to be over-diluted, so there is too little glue left in the joints to effectively bond, so it is not commonly used. Liquid versions of leather glue are now available; usually, they add urea to keep the glue at room temperature and extend the drying time. Examples of liquid leather glue are Old Brown Glue or Titebond liquid leather. The leather glue will not creep. Just heating and adding more rawhide glue can easily realize the repair of rawhide glue joints.

Urea formaldehyde

Urea-formaldehyde resin adhesives are characterized by low effective cost, low curing temperature, resistance to microorganisms and abrasion, and light color. It will not creep and can be repaired with epoxy resin. It quickly deteriorates in a hot and humid environment and releases formaldehyde (a carcinogen).

Resorcinol formaldehyde

Resorcinol-formaldehyde resin glue is very strong and durable (resistant to immersion in boiling water, weak acid, salt water, solvent, mold, fungus, ultraviolet light, etc.). It must be mixed before use (liquid resin and powdered catalyst). It has a deep purple color and may be offensive in some uses. poisonous. [7] For many years, the US Federal Aviation Administration (FAA) stated: “Certified resorcinol is the only known adhesive recommended and approved for use in wooden aircraft structures, and it fully meets the necessary strength and durability. Sexual requirements". However, in fact, the vast majority of wooden airplanes (mainly amateur airplanes) manufactured in recent decades have changed to use other types of adhesives (mainly epoxy resin systems), which have higher strength and more importantly Yes, less critical technology in perfect application. Compared to resorcinol, most newer adhesives are more tolerant of typical construction errors (for example, small gaps or misalignment between parts) than resorcinol, which can hardly be tolerated by the latter Class daily structure situation. This can cause great difficulties, especially in complex assemblies. However, resorcinol is still used by some manufacturers/restorers and is common in older aircraft.