Popular Woodworking 2009-08 № 177, страница 50

highly decorated wood furnishings. Early Native Americansused asticky substance to help hold the seams together in theirbirch-bark canoes.

The first commercial glue factory that specialized in manufacturingglue from the hides of animals began in Holland in the early 1700s. [n 1910 a new product called Bakel ite was deve loped. This began t he plastic era and within a year plastic resins were introduced into the market. During World War 11 there wasan urgent need lo develop new synthetic products such as polymers and rubbers that could be used to hold all types of materials together under a variety of conditions.

But it was the Space Age t hat really blasted the adhesive industry inlo lhe stratosphere. Mosl of lhe glues that are now commonly used in the woodshop were developed within the last 60 years.

Today there are many different types of glues includingwhiteand yellow polyvinyl acetate (PVA), hide or animal glues, resin glues such as urea formaldehyde, epoxies, poly urethanes, super gl ue s (cya noac rylate) and contact adhesives.

These seven familiesofgluesare the focus of this article. Each varies in how it dries, gets hard or cures, and all have different characteristics when exposed to heat, water and solvents. Once finally cured, each has a different degree of rigidity or flexibility

in the ways that it transfers and distributes stresses.

Remember, you don't have to limit yourself to just one type of glue throughout the entire project. Variety is the key to using modern adhesives

How Glues Work

In order Tor adhesion to work, some type of action has to take place between the mating surfaces wilh the glue asthe Lie I used to envision that adhesion was purely a mechanical process where the wet liquid glue penetrated the porous surface of the wood through the pressure ofthe clamps. Then when it dried, tlanchored itsel f tothe pores by holdingthem lightly logether. Bui it's a little more involved than that.

There is also a natural phenomenon that takes place through someihingcalled specific adhesion. Specific adhesion is the natural attraction of similar molecules that are held together and can't be pulled apart - imagine two panes of glass and how they cling together. To separate them, the panes would have to he slid apart.

Now imagi ne that those two panes of glass are separately exposed toair, dust and dirt. Once Lhey are broughi back logelher they can easily be pulled apart.

Speci fie adhesion depends on ih ree main factors: intimate contact, compatibility of mating materials and two clean surfaces.

"In the world of woodworking, 'What's the best glue' is one of the toughest questions

If adhesion is the process of glue bonding to the wood, then cohesion involves the buildingofa strongnetwork within the glue, reaching from one piece ofwood to the other.

Glues for the most part complete the job after the glue turns from a liquid to a solid and cures hard. There are basically three ways this occurs. Be aware that some glues cure through multiple curing processes.

Evaporation. Any glue thai contains waier or solvent (such as PVAs and contact adhesives) dries when the fluid ii contains is spread and evaporates into the air or is absorbed into the fibers of the wood. The

One ofthe earliest. Stiff a big player in woodworking today, hide glue is held in high esteem by true period reproduction furniture makers and luthiers.

A trick in reverse. Polyvinyl acetate glues dry as the water evaporates from the emulsion, If you wish to extend your "open time," purchase a glue that indicates a longer open time.

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