Gluing-Up

Clamping and Curing Times
 
With the exception of cyanoacrylates, contact cements and quick-set epoxies, virtually all glues require pressure to achieve the best bond. Aliphatic & polyvinyl resins should be clamped for about an hour -- slow set epoxies, mastics and liquid hides, 2-4 hours -- and liquid hides and urea glues 12-16 hours.

The curing times of glues vary from one minute for hot-melts to 24 hours for practically every other commonly used glue. Most woodworkers would agree that virtually all glue-ups should be left for 24 hours before machining or applying a finish.  These curing times, can, of course, be affected by temperature. The warmer it is, the faster the glue will set-up. Applying glue below the manufacturer’s recommended temperature will prevent the glue from flowing into the wood grain properly, resulting in a weak joint. Also, glues that normally dry clear, could dry “milky” if the temperature is too low.

Joint reinforcement
 
A joint that’s been properly glued-up will be stronger than the wood itself  when dry.  Still, glue joints should be reinforced whenever possible. Reinforcement adds to the gluing surface and strengthens the glue bond. 

This reinforcement can be done in various ways by using biscuits, dowels, splines or glue blocks. Joints can also be made stronger by choosing specific types of joints such as dovetails, tongue-and-groove, mortise-and-tenon, finger-laps, half-laps and others are stronger than a standard butt joint for one reason -- they increase the amount of gluing surface in the joint substantially. Nails and screws help some, but they make better clamping devices than joint-strengtheners.

Some valuable gluing tips

1. Choose the right glue for the job (see table)
2. Never glue up damp or green wood
3. Prepare your mating surfaces properly.  Be sure they’re clean, dry and free of foreign materials.
4. Always spread glue evenly
5. Avoid applying too much or too little glue
6. Clamp glue joints snugly, but not too tightly
7. Some projects can be glued without clamps, but clamping is almost always recommended for the best bond
8. Check your glue’s shelf life before use

Table of Glue Types, Uses and Limitations