If you are working with wood, whether repairing or building, there are a variety of items you may need. If you are bonding wood together or repairing broken wood, you might need to use either wood glue or wood filler. The thing to keep in mind, though, is that while both are very useful substances, they are not the same thing.
As such, they are not interchangeable. Let’s figure out when wood glue is called for and when to use wood filler.
Wood Glue and Wood Filler: The Basics
Before we talk about the similarities and differences, let’s first figure out what both wood glue and wood filler are.
What Is Wood Glue?
Wood glue, as the name implies, is of course a type of adhesive.
The traditional type of wood glue is PVA or polyvinyl acetate. These are also known as aliphatic resins. They are great at adhering wood together, but won’t stick to non-porous materials. It is used to bond wood and is often used in combination with nails or screws. Normal PVA glue is not overly moisture resistant, but there are special kinds that are.
The other common type of wood glue is polyurethane glue which actually dries via chemical reaction when it comes into contact with moisture. This type of wood glue is very water-resistant, although it tends to expand as it dries.
What is Wood Filler?
Wood filler, unlike glue, which is an adhesive used for bonding, is a substance designed to fill holes, cracks, and voids in wood that requires repairs.
Wood fillers can be made out of various substances. However, they are commonly made out of pulverized wood pulp that is contained within a binder or resin. This resin then dries rock hard, just as hard as the wood being repaired, if not much harder. One of the benefits is that wood fillers are often sandable and paintable.
Similarities of Wood Glue and Wood Filler
Now that we know what both wood glue and wood filler are, let’s figure out what makes them similar. As you may have figured out by now, they are two very different things.
1. They’re Both Designed for Wood
As the names of both of these substances imply, they are designed for use with wood, and exclusively so. Of course, they don’t serve the same purposes, but they are both commonly used substances in carpentry of all sorts. Both are often used in furniture building and furniture repairs, respectively.
2. The Won’t Adhere to Just Anything
Perhaps the biggest similarity shared between wood glue and wood filler is that they really only stick to wood. They may also stick to other porous materials, very porous materials. This does limit their usefulness, mainly just to wood. They won’t adhere to non-porous materials. You can’t use wood glue or wood filler on slick materials such as plastic, glass, and metal.
3. The Drying/Curing Process May Be the Same
Although not the case 100% of the time, both wood filler and wood glue often cure through simple drying. In other words, they harden through the evaporation of the liquid inside of them. Once all of the moisture has left the substances, what is left is rock hard.
4. They Are Both Workable Once Dry
The other similarity shared between wood filler and wood glue is that they are both workable once dry. Both materials can be sanded and painted once they are fully dry.
Differences Between Wood Glue and Wood Filler
Now that we know what similarities these two substances share, let’s figure out what makes them different from each other.
1. Adhesion Capabilities
One of the biggest differences between wood glue and wood filler is that glue can bond wood together. You can use wood glue to bond two separate pieces of wood firmly together, but wood filler cannot do this. Wood filler, while it will patch holes and gaps just fine, does not have great bonding strength.
2. Weatherproofing
Although not the case 100% of the time, wood glue is usually waterproof and weatherproof, or at least weather- and water-resistant. More often than not, wood filler is not overly so. Wood glue can in some cases be used for outdoor purposes, but wood filler cannot, at least not if you don’t properly seal it from moisture once it has dried.
3. UV Resistance
Another big difference here is that wood glue generally has at least some UV resistance. Wood glue is not the most UV-resistant substance in the world, but still much more so than wood filler. If a wood filler is exposed to sunlight, even in just moderate amounts, it will begin to crack and come undone.
4. One Fills in Gaps, the Other Does Not
Wood filler is quite thick, which means that it doesn’t run down. It stays in place quite well. It is therefore ideal for filling cracks, gaps, and holes. It also dries much harder than the wood itself, thus perfectly repairing wood. Wood glue on the other hand is much thinner and will run down through cracks and gaps. It is therefore not ideal for filling gaps. It also doesn’t dry quite as hard as wood filler.
5. Wood Filler Dries Clear
Wood filler usually dries clear, thus making it ideal for repairs where you don’t want any visual evidence left behind. Wood glue on the other hand, may dry clear sometimes, but may also dry to a yellow color.
6. Wood Filler Has Real Wood in it
The other difference here is that wood filler actually has real wood pulp in it, whereas wood glue has no wood in it whatsoever.
Wood Glue vs. Wood Filler: Which of the Two Should You Use?
Which one of these two substances you use really all depends on what your purpose is. If you are bonding wood together, then it is wood glue that you need. If you are repairing or filling cracks, holes, and gaps in wood, then it is wood filler that you want to use.
Summary
As you can see, both wood glue and wood filler have their specific uses and benefits. Although they are not designed for the same tasks, if you are a carpenter or someone who regularly works with wood, then chances are that at some point in time, you will use both wood glue and wood filler.