Glues and Gluing: Part Two
In the second of this short series of articles on glues and gluing, I’ll be looking at a few more common adhesives that ought to be in your workshop.
For some years, the only glue I had used was the very readily available white PVA. For the most part, it’s great stuff. But then a job will toss you a googly and I found I needed something that worked better. It may not be used regularly, but from time to time, you’ll be glad that you’ve got the right adhesive to hand.
As mentioned in the previous blog, urea formaldehyde (UF) glues have certain limitations. But the overriding advantage is the extremely long open time or usability factor before it starts to set. Conversely, the time taken to make an initial bond is referred to as the ‘grab time’ and can be just a few minutes with some modern glues. When there’s a complicated glue-up in process, an open time of an hour or two (in cool conditions) is a huge advantage.
Water Resistant & Waterproof Glues
Brief mention was made of UF glue’s capacity to resist water, but this doesn’t mean that they are entirely waterproof. For example, if a garden gate were to be made, a UF glue or an adhesive such as Titebond III, would be appropriate as the work isn’t soaking wet all the time. A good degree of water resistance is all that’s needed.
Projects that are continuously immersed, such as a boat hull, require an epoxy adhesive. West System is probably the most well-known for this particular use. These adhesives are true resin epoxies and are ideal for larger projects as well as providing a variety of fillers to bulk out the glue for different applications. For smaller jobs, phenol formaldehyde is a good choice or a polyurethane glue. These have a fast ‘grab time’, are gap filling and 100% waterproof. They also stick to a wide variety of materials.
The big disadvantage with polyurethane glue is that any overspill that contaminates your hands is difficult to remove so it needs to be applied with some care! The alternative is to use latex gloves. Very small gluing jobs can be tackled with twin tubes of two part epoxy, either traditional slow setting or a rapid variety. They’re also very good for gluing dissimilar materials together such as wood to metal, where a permanent and very strong bond can be achieved.
Hot Melt Glue
I’ve had a hot melt glue gun in the workshop for decades and it’s another one of those indispensable gluing systems. But great care should be taken, as the hot glue ejected from the nozzle is very hot! It will instantly stick to anything, including plastics, which are notoriously difficult to glue. Once the glue’s cold, the joint’s complete. Hot melt glue is great for model making and all sorts of other applications where a strong, instant bond is needed. The picture shows the Heath Robinson extraction hood for my lathe made from an old plastic funnel and a section of 100mm clear tube. This is entirely glued together with hot melt adhesive.
Even quicker are ‘super glues’, or cyanoacrylates, which were first developed during the Vietnam war for medical use. They’re available in different viscosities and some can be made to set almost instantly by using an accelerant. As with polyurethane glue, care needs to taken when using them, as they have a great affinity for human skin.
The last type of glue, which is worthy of inclusion, is the impact variety. These are useful where large surface areas need to be glued. For example, gluing a hard wearing laminate to a ply or mdf substrate. They will also stick a very wide range of different materials together. In recent years, this type of glue has received a bad press with regard to certain types, which rely on a solvent evaporation before the surfaces to be joined, are brought together. If this type of glue is used in the workshop, there must always be adequate ventilation. It doesn’t take long for the fumes to take detrimental effect. There are now impact adhesives that are solvent free, and equally as effective, but without the obvious H&S disadvantages.
The modern woodworker is really quite spoilt for choice these days regarding the adhesives at his or her disposal. Many adhesives will join a variety of different materials. Some may have a longer or shorter ‘grab’ time; some a longer or shorter ‘open’ time; and many are waterproof to a greater or lesser extent. Used with care, they’ll stick similar or different materials together with an extremely powerful bond. In many instances the bond is so great it’s almost impossible to separate them again.
The last article in this short series will deal with ways of applying glue. Also it will look at effective strategies for removing unwanted glue from a project once it has been applied.