Choosing the right glue; making it stick. Almost anything that fits together can be glued. It’s a matter of choosing the right glue for the material and of using it properly. But glue is no substitute for a well-made joint; no glue will hold two pieces that don’t fit.
Moreover, a joint must be held firmly until the glue sets. Most wood glues require clamping for several hours. Contact cements bond instantly; no adjustment is possible once contact is made. Try to glue on a dry day. Even if humidity doesn’t weaken the glue you’re using, it might affect the material you’re working on.
Before applying any kind of glue, practice putting the pieces together in the allotted tim. If they are to be clamped, decide what clamps to use, how to use them, and in what order. Then try it without glue.
To keep from marring surfaces, tape small wood blocks on the clamps’ metal jaws. To keep from gluing a piece to the bench, place wax paper or plastic wrap under the joint; sandwich some between the wood blocks and the workpiece too.
If you lack the clamps needed for a job, you can probably improvise with wedges or a tourniquet. To make a tourniquet, wrap twine twice around the piece and tie it. On both sides of the piece, insert wooden pegs (broken pencils will do) between the two strands of twine. Exert pressure by winding the twine with the pegs, alternating sides to keep the pressure even.
When joining wood, apply a coat of glue to each piece and tighten the clamps gradually, first one, then the other to keep the pressure even. Continue tightening the clamps until a thin line of glue emerges, but do not over tighten them; a “starved” joint-one with the glue squeezed out-won’t hold. Wipe off excess glue with a damp cloth. (On wood that is to be finished clear, however, it is better to let the glue dry, then slice it off with a chisel.)
Instant glues and quick-acting epoxies, meant for joining such non-ferrous materials as glass and metal, can usually be taped or hand-held; slow-acting epoxies require some kind of clamping. The formulas of these products vary, as do the setting times and the lists of materials they will join; read and follow the directions on the container.
Caution: The fumes from some glues are dangerous. Always use glue in a well ventilated area, never near open flame. Instant glues bond to the skin; never point a glue tube toward your face.