Wood glue plays the all-important role of bonding pieces of wood. However, despite their undeniable importance, these adhesives tend to thicken, which can make them hard or even impossible to use. So how do you thin wood glue?

Here are several ways to thin wood glue:

  1. Tap the glue container on a wall.
  2. Add water to the glue.
  3. Add a spoonful or two of vinegar to the glue.
  4. Heat the glue in a bowl of warm water.

Thinning wood glue largely depends on the type of glue you’re using. Keep reading as I discuss various ways to thin glue and make it easy to use. I’ll also cover different glue types to help you determine the best method for thinning and how to prevent thickening in the first place.

1. Tap the Glue Container on a Wall

This is the first step that can help make the thinning process a lot easier. And while this method isn’t guaranteed to thin your wood glue consistently, it can help reduce overall thickening and make the glue a lot easier to use.

Take the glue container and gently tap it on the wall. Repeatedly doing so will help loosen the glue’s bonds. However, this method won’t work if the glue has thickened up completely. Either way, it’s a great way to kickstart the thinning process and make your work easier.

2. Add Water to the Glue

Water is arguably the most commonly used thinning method for glues. It works well for water-based glues, especially if you add just the right amount of water. Ideally, you should add water up to 5-6% of the glue’s volume or weight.

There are two ways to go about it. First, you can add water to the glue inside the container (if you plan to use the entire glue), or you can place a bit of glue on a bowl and add 2-3 parts water (depending on how thin you want it to be).

Keep in mind that adding too much water to wood glue will almost certainly weaken the glue’s bonding properties, making it less ideal for use in projects that require firm bonds. 

For instance, if you’re thinning Elmer’s Carpenter’s Wood Glue, you might start by placing the amount of glue you want to thin in a clean container. Next, add a small amount of clean water and stir to see if the mixture delivers the type of consistency you’re after.

If it’s not thin enough, then continue to add a small amount of water and stir, repeating until it’s perfectly thinned. And if you end up thinning the glue more than needed, you can always add a spoonful of the adhesive to the container and mix until it reaches the desired thickness.

3. Add a Spoonful or Two of Vinegar to the Glue

If you’re dealing with wood glue that’s completely thickened, then you might have to get a bit creative and add a spoonful or two of vinegar. While this method isn’t advisable as a first resort, it can help you when looking to salvage glue that’s almost thickening out completely.

The first step when thinning wood glue with vinegar is to place the glue in a clean enough container. You can then add water and stir to see if the glue thins out accordingly. If it’s still thick, you can add a spoonful of vinegar to the mixture and stir for a minute.

If the mixture is still fairly thick, you can add another spoonful of vinegar and stir again. You’ll soon begin to notice the wood glue gradually thinning as you continue to add vinegar to the mixture. 

4. Heat the Glue in a Bowl of Warm Water

This method is ideal for liquid hide glue and not other types of wood glue. You’ll need to be careful when heating the glue as too much heat might end up thickening it as opposed to making it thinner.

When using this method, you’ll first need to heat the water and allow it to cool in a bowl. After the water has cooled down a bit, place your liquid hide glue inside and allow it to stay for 5-10 minutes.

If the water cools and you’re not satisfied with the thinning consistency, add some hot water, but take care not to make the water extremely hot.

Types of Wood Glue

Thinning wood glue is a great way to bring it back to life and increase its adherence. However, when looking at thinning wood glue, it’s crucial to consider the type of wood glue you’re using, as not every method is suitable.

Polyvinyl Acetate Glue (PVA)

Polyvinyl Acetate (PVA) glue is arguably the most common type of wood glue. Some of the common types of PVA glue include Titebond, Gorilla Glue, and Elmer’s glue, which have been used in creating and repairing wooden furniture.

PVA wood glue doesn’t yellow after usage and tends to remain flexible, ensuring it maintains its sheer strength long after application. PVA glue is preferred for its mild nature in the woodworking world as it is both odorless and colorless, making it great for internal and external projects.

Some types of PVA wood glue are water-resistant, while others aren’t waterproof enough to be used on outdoor projects. Either way, the type of PVA glue you use will depend on the nature of your project and the glue’s availability and features.

Polyurethane Glue

Polyurethane glue is usually activated by moisture and is known to be waterproof, making it a great option for outdoor projects. This type of glue cures as a result of a chemical reaction with moisture, making it a perfect fit for bonding oily woods or those with high moisture content.

When using polyurethane glue, it’s crucial to give the glue enough time to cure, especially when dealing with oily woods—cleaning up excess glue after usage is also highly recommended if you want a neat finish.

Cyanoacrylate Glue (CA Glue)

Cyanoacrylate glue is known for its good holding properties but doesn’t rank too well in terms of sheer strength. As a result, CA glue is mostly used to glue wedges to pieces of wood for use as clamping assistance.

You can also use CA glue for furniture repair, trim, inlays, and crown molding since it’s clear and tends to dry quickly. The Bob Smith Insta-Cure is an example of a commonly used CA glue.

Hide Glue (Rawhide Glue)

Also called animal or rawhide glue, hide glue has been around for several years and continues to be used by some traditional woodworkers. Liquid hide glue is commonly used in woodworking and is preferred for its gentleness on wooden surfaces.

Although not the strongest wood type, hide glue can still hold two pieces of wood well enough. However, you’ll need to give the glue more time to cure to ensure a secure bond.

Epoxy Glue

Epoxy glue is made of two parts, a hardener and a resin. Once the two parts combine, they create a strong chemical reaction, thereby creating waterproof glue ideal for filling cracks, holes, and dents in the wood. A point to note, though, epoxy glue doesn’t work too well on acidic surfaces or extremely moist planks of wood.

How to Tell When Wood Glue Is Beyond Thinning

While wood glue can be thinned on most occasions, there are some instances when you’re better off throwing the entire container away, as explained below:

  • When the glue becomes excessively thick: Glues also have their expiration dates, and you’ll know your adhesive is already expired if it’s overly thick and won’t run at all. In such situations, you should discard the container as the glue won’t be of much use.
  • If the glue isn’t adhesive: If you try sticking an object with your wood glue and it doesn’t adhere, then it’s time to get another glue, as thinning won’t help you out.
  • When the glue looks separated and lumpy: If your wood glue becomes separated and lumpy, chances are good that it’s already expired and won’t benefit from being thinned.

How to Store Wood Glue to Prevent Thickening

If you don’t want your wood glue to thicken excessively, then it’s best to check on your storage practices.

As a rule, you should always try to squeeze out excess air from the container before sealing. Another crucial rule to observe is sealing the container tightly before storing the glue in a location with a constant temperature.

Wrapping Up

Thinning wood glue largely depends on the type of glue you’re using. Adding water to water-based glue tends to work best, especially if the glue hasn’t thickened out excessively.

Other methods you can use include taping the container on a hard enough surface to help break the bonds. Some woodworkers swear by adding spoonfuls of vinegar to glue water solutions to thin out the glue.

Whichever method you prefer, it’s best to mix in clean containers. Be sure to properly seal and store wood glue to prevent thickening from occurring.

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