It is important to keep a couple of things in mind before gluing a joint. First is that while modern glues are extremely strong, it will not compensate for a poor joint. If joints do not fit properly or the glue is not cured correctly, chances are that the bond will fail. The second point to keep in mind is that less is more. By applying a thin, even layer of glue you will achieve a stronger bond than using a thick layer of glue. The thicker the glue the more cushion and the less effective the joint will be.
Start With A Properly Fitting Joint
In order to achieve a successful joint you make sure that the surfaces of both parts fit correctly. You do not want to rely on clamps to pull warped or locked pieces together. This will place too much strain on the joint and it will actually fail. The trick is not to make the joint too loose or too tight. If the parts need to be forced together, there will not be enough room for the glue to bond the two surfaces. Conversely, a loose fitting joint will cause too much room and the glue will end up being too thick. The perfect joint is one that will allow for a layer of glue that is about the thickness of a sheet of paper. To ensure that the joint receives the proper amount of glue, spread a thin layer of glue on both of the adjoining pieces. You can use a small brush or roller to make sure the glue is the correct thickness; just make sure that the coating is complete and even.
Make Sure the Surfaces Are Clean
Nothing can affect the bond of any joint more than a contaminated surface. It is vital that all surfaces are clean and dry before applying the glue. Oil, waxes and some chemicals like silicone will resist glue. Dust and water on the surfaces can prevent a good contact between the parts, causing the bond to fail. If contaminates are found, lightly sand the joints to remove the contamination, then give the area a light sweep with a tack cloth. It is important that you do not rub the surface with the cloth or you will leave a sticky residue.
What Is Open Time?
Simply put, open time reflects to the length of time glue can safely be exposed to the air before assembly. The open time is different for various glues, so make sure you find this out before to start the assembly. This will let you know how much time you have to complete the process without compromising the strength of the bond. The rule of thumb for most yellow glues is about ten minutes, but environmental conditions can affect the open time.
The temperature and humidity of your workroom must be taken into consideration. In hot and dry conditions, glue will setup quicker. If you have several complicated assemblies with multiple joints, it is critical to factor in the open time. If you feel that the open time may not be adequate for a complicated joint, you may need to break down the joint into smaller sub-assemblies. Beside open time, temperature can also affect the bond. Most types of yellow glue are not effective in colder conditions. The general guideline is that the glue and the surfaces being bonded should be at least 55 degrees Fahrenheit.
Final Assembly and Clean Up
After the joint is glued and assembled, use clamps to hold the joint until the glue has cured. Clamps will ensure that the joint is folded together properly and they will hold the parts in a fixed position until the glue sets. It is important not to use too much pressure on the clamps because you will force too much glue out of the joint, lessening it holding power.
If you have used the proper amount of glue and the correct amount of force on the clamps, a small bead of glue should be visible on both sides on the parts. You may be tempted to wipe off the excess glue immediately, but just be patient. Allow the glue to setup for about 20 minutes; then use a putty knife to scrap away the excess.
There are some that recommend wiping off excess glue with a damp cloth, but I do not agree with this thinking. Using a damp cloth can actually force the excess glue into the pores of the surrounding wood. While this will not be noticeable at first, it will become obvious when applying the finish. Glue will not absorb the finish like the wood and by then it is too late to correct the problem.
Before removing the clamps, check the drying time for the glue you are using. Most yellow glue should remain clamped for at least an hour. After that you can remove the clamps, but you should allow a full 24 hours for the glue to cure completely.
Source by Alan J. Douglas