Shane quickly discusses the pros and cons of three types of glue
In this video, Shane talks about three categories of glue we use in the furniture workshop all the time:
- PVA (polyvinyl Acetate)
- Animal Glues
There isn’t just one glue to use in all situations. They have different properties, and it can be intimidating to try to wrap your head around it all. While not going into all the details, we have decided to give a quick introduction to three common categories. It is important to know what advantages and disadvantages these glues have so that you can feel confident you are making the best choice.
PVA (Polyvinyl Acetate)
PVA glues are the most common wood glue you will find. If you buy something called “craft glue” or “wood glue” either by a brand like Selleys or Titebond, there is a high chance of likelihood it is a PVA glue. These glues are usually water-based and will appear milky or sometimes brown/yellowish (depending on what has been added to them). In fact, the polyvinyl acetate is mixed into water, but not fully dissolved in it. When it is applied to the timber, the water will soak in or evaporate, leaving the adhesive drying on the surface.
PVA has great bonding power and will bond really well with timber. As you may have seen in Luke’s video about trusting glue strength, once the glue has properly dried, it will be stronger than the timber itself. The water-based nature of PVA along with its bonding strength is what makes it a great go-to for most common repairs and jobs in the workshop. Some PVA glues have additives which make them more water-resistant, and these are often sold as ‘Exterior Wood Glue’
The two downsides to PVA are that it is not very reversible, and many versions will not naturally degrade in the environment well. There are times in woodworking, where we want to be able to take apart of joint later on, and PVA will not make that easy. The best wood adhesives there are protein glues.
Animal (Protein) Glues
Animal based glues are the most common wood glue in history. Glues derived from animal or fish proteins have been used for thousands of years and were what you were referring to if you said the word “glue” until the mid 1900s.
Taking these naturally strong and sticky proteins, we can make a very strong and reversible glue for furniture. The glue is sold in a solid state. You then add water and heat to it until it becomes a thick liquid (similar to honey), and it can be applied to a timber joint with great results. Once the glue has cooled and dried, it will hold with great adhesive and cohesive strength.
The benefit here, is that if you needed to take that joint apart later, you can add warm water and heat to the glue, and it will come undone. Animal glues will also biodegrade more naturally in the environment.
Animal glues can be a little more brittle than PVA, and they do of course come from animals. So if you are vegan, or have other objections to using animal product, this is not the product for you. There are some other natural glues which are not animal based (funori in japan for instance) but we do not cover these in this video.
Epoxy is often our last resort adhesive, or something we use in very specific circumstances. It is known for being very strong and durable with high bonding capacity to a lot of materials.
Epoxies always come in two parts: The epoxy resin and some kind of hardener or catalyst. You have to mix these two components together before applying the epoxy to the timber, but once you do it will start to chemically harden, so your working time can be quite short. The epoxy will be very hard and can fill gaps that the previous glues will struggle with.
It is definitely not reversible though, and does not break down easily in nature. Almost all epoxies will deteriorate and yellow over time without special additives. They can often be too hard or brittle for an object. Wood has a natural flexibility which epoxy doesn’t. This can lead to other breaks, cracks, and adhesive failure later on.
There are many other glues out there, like superglue and polyurethane, but we stuck with these for this video as they are our most commonly used in the workshop. If you are interested to know more about other glues, please let us know in the comments.