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Wood Glue vs. Wood Filler: What’s The Difference

For your latest woodworking endeavor, you’ll need to join two separate planks of wood. If you need to repair some wood, should you use wood glue or wood filler? Wood filler and wood glue seem similar, but what really sets them apart?

Here are some distinctions between wood glue and wood filler:

Wood filler won’t hold wood together, but wood glue will.
Unlike wood filler, wood glue can withstand the elements.
While most wood glues offer some degree of resistance to ultraviolet light, wood filler will dry out and crack if left in the sun.
When comparing wood filler versus wood glue, keep in mind that wood filler actually contains wood fibers.
When it comes to patching up holes and cracks in wood, wood filler is far superior to wood glue.
In contrast to wood glue, wood filler never becomes white when it dries.
Below, I’ll define wood glue and wood filler and discuss their differences in detail. As for whether or not you can use wood glue for wood filler, I’ll go over that, too. If you can help it, don’t miss this!

Glue for wood versus wood filler

What Is Wood Glue?

Let’s start with the basics by defining what wood glue actually is. Wood glue, as the name implies, is an adhesive that can be used to join two different types of wood.

Some varieties of wood glue are also intended to fill up holes and gaps, much as wood fillers. It is understandable why amateur woodworkers would confuse these materials.

There are many different kinds of wood glue available on the market, and the one you choose should be based on the task at hand. Materials like resorcinol-formaldehyde resin glue and urea-formaldehyde resin glue are examples of aliphatic resin glues.

These are certainly well-known terms, but don’t worry; I’ll define them all below.

Aliphatic Resin Glue

Aliphatic resin, the first type of glue, is quite typical. Aliphatic resin employs an aliphatic component to bind to wood; other common names for this product are yellow glue and carpenter’s glue.

Aliphatic resin, also known as “yellow glue,” gets its name because it dries to a yellow color and a creamy, almost soft consistency.

Brands like Lepage and Titebond are frequently seen when searching for aliphatic resin glue. Aliphatic resin has much less creep than white household glues like Elmer’s.

What type of wood glue should be used
Moreover, it sets rapidly between 50 and 110 degrees Fahrenheit (10 and 43 degrees Celsius). While aliphatic resin glue is an unusual option for wood glue, it is not suggested for usage in the outdoors. What happens when wood glue freezes? Click here to find out!

The glue is thick and doesn’t run very easily. Aliphatic resin has excellent resistance to water, fire, and even some moisture. It’s not the best at bonding, but it works well enough, isn’t flammable, and has almost no smell.

Be sure to rinse the glue bottle with running water before using it to cure the aliphatic resin. In addition, you will need to sand any unwanted glue globs off your woodworking item. Wood stain applied directly over glue will not absorb, resulting in an unattractive finish.

Polyvinyl Acetate

Polyvinyl acetate is still another choice, albeit it is not advised. This is due to the fact that PVA glue, also known as craft glue, is typically only used for hobby purposes. It’s the same white glue mentioned in the previous paragraph. In spite of its creepy nature, PVA glue dries quickly and is totally safe to use.

When PVA glue dries, it prevents other wood glues from sticking to whatever it was glued to. Because even PVA glue won’t stick to dried PVA glue, you’re in a jam.

Cyanoacrylate

Superglue and crazy glue are common names for cyanoacrylate, which describes its bonding properties. Esters, such as ethyl cyanoacrylate, are the source of this glue. Small repairs can be made to a woodturning or other woodworking project with cyanoacrylate glue.

Cyanoacrylate is a popular wood adhesive for model making with balsa wood. The strength of this adhesive, in comparison to balsa wood, is the reason for this.

The binding can actually be weakened by using too much cyanoacrylate. Using too much glue weakens the bond, while using too little adhesive also weakens the bond.

Because of its brittle nature, cyanoacrylate is already at a disadvantage. Cyanoacrylate glue can split and come undone if you glue multiple pieces of wood together and then attempt to bend one of them days or weeks later.

One advantage of dealing with cyanoacrylate is that it doesn’t have a powerful odor. Cyanoacrylate, unlike certain other wood glues, does not polymerize quickly. If you wish to use cyanoacrylate to fill a hole in wood, but the glue itself is too leaky or runny, try the gel kind instead.

Cyanoacrylate is extremely sticky and should not come into touch with any exposed skin. The glue dries instantly, so it’s possible to accidentally stick your fingers together if you use too much of it.

Polyurethane

Polyurethane glues like Excel and Gorilla Glue have become standard in the woodworking industry. This glue is not limited to simply wood; it also works on rubber, pottery, sand, glass, plastic, metal, and even fibers in textiles. In that case, it can serve multiple purposes.

To be sure, polyurethane glue isn’t the strongest option, but it can get the job done if you need it to.

Resorcinol-Formaldehyde Resin Glue

Resorcinol-formaldehyde resin glue is superior to polyurethane glue when it comes to adhesion. It is resistant to UV light, mold, mild acids, solvents, salt water, and even boiling water.

Of course, you can’t just open the package and start applying the glue. Instead, it needs to be activated by combining powdered catalyst with liquid resin.

You have to be careful not to leave any traces of the purple-drying resorcinol-formaldehyde resin adhesive behind. It’s not great for your lungs either, so make sure you have plenty of fresh air to breathe while working with this glue.

Urea-Formaldehyde Resin Glue

Urea-formaldehyde resin glue is another comparable material. Urine is the source of the resin known as urea-formaldehyde or urea-methanal. Get over that and you’ll see that, unlike resorcinol-formaldehyde glue, this wood glue doesn’t turn anything purple.

It doesn’t become abrasive, cures in lower temperatures, is inexpensive, and doesn’t creep. For a long time, this glue has also been the gold standard for putting together wooden airplanes.

What Is Wood Filler?

Wood filler is up next, so let’s talk about that. Wood filler can be used to fix imperfections like dents, chips, and nail holes in wood. Open-grained wood may also be absorbed by this product.

Wood filler is an indispensable tool if you frequently work with mahogany or oak.

Ultimately, you’ll need to decide between two distinct wood fillers. Wood filler used to seal cracks and holes will be thicker than filler meant to cover wood pores. The former resembles pancake batter in consistency, whereas the later is denser and more like to putty.

The two terms are often used interchangeably, however wood filler and wood putty are two distinct products. Even more commonly than wood glue and wood filler, these two materials are often mistaken for one another.

If you want to know the difference between wood putty and wood filler, check out my analysis here. Ingredients make all the difference.

Wood filler typically consists of a binder with wood fibers or sawdust, while wood putty typically has a basis comprised of polyurethane, fiberglass, epoxy, or plastic. Wood fillers, once applied, will harden or cure over time. Putty made from wood does not dry out like wood filler does.

Wood fillers like Famowood are common. Wood flour, or wood particles that have been reduced to a powdery consistency, is an ingredient in this product. As a binder, the nitrocellulose lacquer in Famowood is essential. You can use this wood filler, or one like it, on many different kinds of wood. It dries rapidly and causes minimal shrinking.

Some wood fillers, like Wunderfil, actually contain putty. Wood filler can be thinned with water for use in filling in knots and other imperfections in wood.

Otherwise, a dual-purpose wood filler like Wunderfil can be used straight from the bottle to patch up any holes or cracks in your wood. Wood fillings that are thinner than water may contain varnish or oil.

Most wood fillers come in a range of natural wood hues designed to blend seamlessly into the wood you’re working with, and may be purchased in a variety of thicknesses. When they dry, many fillers won’t leave any sort of tinted residue either. There are even some with a shiny, alluring coating.

Check to see if wood filler can support a screw.

What Are the Differences Between Wood Glue and Wood Filler?

Now that you know what wood glue and filler are, we can go into more detail about the differences between the two that we briefly discussed in the introduction.

Wood Glue Is For Adhering, Wood Filler Is Not

As we’ve established, some types of wood glue can be used to fill gaps, so the substance does have some versatility. However, wood glue is typically only used to join other pieces of wood together.

Obviously, wood filler won’t suffice. Although it can hide the defects in rotten or otherwise poor wood, it cannot join the pieces together.
Wood putty, which is not wood filler, is tackier than wood filler, but it is not the same as wood glue.

Wood Glue Is Weatherproof, Wood Filler Isn’t

When it comes to using the product outside, wood glue outperforms wood filler in terms of waterproofing. Water is permitted to be used with wood filler because many wood fillers can be thinned by mixing with water. In contrast to typical wood glue, however, it has not been subjected to submersion testing.

Wood glue is more weather-resistant than wood filler, so use it if you plan to display your finished product outside. Lots of glues are waterproof and weatherproof, therefore your project will be fine if you use wood glue.

Wood Glue Has UV Resistance, Wood Filler Does Not

The UV resistance of wood glue and wood filler is another distinction between the two. As effective as wood fillers are, they can have unintended consequences if treated wood is left in the elements for too long.

It is possible for the wood filler to dry out even further, at which point it would become brittle and crack. The final appearance of your woodworking product may suffer as a result of this.

UVA and UVB rays don’t damage many forms of wood glue. Wood glue is what you need if you’re building a wooden bench to put in your backyard.

Wood Filler Includes Wood Fibers, Wood Glue Does Not

One key distinction between wood filler and wood putty is the presence of wood fibers or even wood flour in the former. There are many different kinds of wood glue available, but none of them actually include wood fibers.

There was once a sort of wood glue available, called casein glue, which was similar to other types of glue but instead of wood grains, it used phosphoproteins like those found in dairy products.

Wood Filler Often Fills in Holes and Gaps Better Than Wood Glue

Wood glue could be used to fill in a gap if absolutely necessary, as we’ve discussed. It’s also possible that it won’t.

Many wood glues have the unfortunate property of temporarily filling a gap when wet, but drying causes the glue to seep deep into the wood. The structural integrity of gap-filling glues may be questionable, especially when compared to wood filler.

Some woodworkers choose to add structural fillers to epoxy resin glue to make the resin even thicker and heavier. This resin now functions more like a wood filler, but only after a great deal of work has been put in. Rather than spending time and effort filling in holes, you can buy wood filler instead.

Keep in mind that wood filler was created for the sole purpose of sealing cracks and gaps between wood grains, no matter how minute. The results will be much superior to those achieved with wood glue.

Wood Filler Dries Clear, Wood Glue Doesn’t Always

Picking the right glue for your woodworking projects requires some thought. Aliphatic resin dries yellow, while polyvinyl acetate residue can be white. For example, resorcinol-formaldehyde resin glue is the most eye-catching because it is purple while wet and stays purple when dry.

Wood filler has the added benefit of drying transparent and looking quite similar to the wood’s natural color. It’s completely discreet; no one will ever know you’ve used it.

Conclusion

As two distinct products, wood glue and wood filler are not compatible with one another. Wood glue is dependable for bonding wood together, and the bonding strength can vary depending on the type of glue used. Gaps in wood can be filled with some wood glues, but usually not very successfully.

Wood filler is intended for smoothing gaps and filling in spaces between wood grains in some types of wood like mahogany. Unlike wood putty, wood filler dries hard. It also contains wood fibers in the formula.

Ideally, you should have both wood glue and wood filler handy in your workshop so you can use either product when the need arises. Best of luck!

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