Understanding wood glue + 8 awesome tricks you should know

Understanding wood glue + 8 awesome tricks you should know


Every woodworker is guaranteed to have already worked with it.
Wood glues are in fact indispensable in the workshop of the woodworker.

As with paint, there is also a difference between wood glue for indoor and outdoor use.
Besides that, there are also many differences such as drying times and applications.

In this article, I will cover everything there is to know about wood glue.
I will discuss what types of wood glue are available, and I will go deeper into their application.

In addition, I share with you 8 awesome tricks you should know.

After reading this blog, you will never have problems understanding Wood Glue, and you know perfectly which glue is suitable for your job!

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How does wood glue work?

Wood glue is an adhesive used to firmly bond pieces of wood together.
But how exactly does that type of glue work?

Simply put, bonding occurs when glues penetrate the surface into healthy wood two to six cells deep.

After penetration of the wood, the moisture in the glue evaporates through the wood fibers or wood grain.
This ensures that with sufficient pressure, a super-strong connection is created between the parts to be glued.

The strength comes from the adhesion to the material and its own strength.
With a good glue connection, the wood connection to be glued will be stronger than the wood itself.

Wood glue classes

When you buy wood glue you can see D2, D3, or D4 on the bottle.

These grades are part of the European standard BS EN 204.
That regulates the classification of wood adhesives for non-structural applications.

This subdivision into D-classes is a quick way to notice the different properties of an adhesive.

Understanding wood glue + 8 awesome tricks you should know

You will wonder, what the hell does that “D” mean?
In the case of glues that can be used to glue wood, the ‘D’ stands for durability.

Wood adhesives are divided in this way into 4 main types of sustainability grading.
These go from D1 to D4.

To give a better insight into the differences between these 4 main types, I describe them below:

  • D1: Only use in indoor areas, where the temperature only occasionally exceeds 50 °C for a short time, and the moisture content of the wood is maximum 15%.
  • D2: Indoor use, with occasional brief exposure to running, or condensed water, or occasional high humidity, provided that the moisture content of the wood does not exceed 18%.
  • D3: To be used in indoor areas, with frequent short-term exposure to running or condensed water or heavy exposure to high humidity. Outdoor areas not exposed to weather.
  • D4: Indoor areas with frequent prolonged exposure to running or condensed water. Outdoor areas exposed to weather.

What types of wood glue exist?

PVA Polyvinyl acetate

PVA (stands for “polyvinyl acetate”) glue is best known to most woodworkers.
This is the well-known white wood glue that has the thickness of a paste that dries colorless.

To guarantee a good glue connection with PVA glue, it is very important that the glued parts are clamped together well, and that there is always good contact between both parts.

Therefore, PVA glue is not suitable for filling cracks or bonding uneven surfaces.

Polyurethane

Polyurethane glue normally has a D4 classification.
As I just indicated earlier in this blog, D4 adhesive is a waterproof construction adhesive suitable for wet applications.
In addition, Polyurethane glue is widely used for gluing wood to other materials.

This type of glue is about as strong as PVA glue, but the effect and color are different.
Pay attention when you use this glue because the brown color can leave stains on your wood.

The Polyurethane adhesives are available in one-component and two-component systems, with a second element added to the two-component adhesive to speed up curing.

Polyurethane glue reacts with the moisture in the air, causing it to foam and harden. 
The foam ensures that gaps, cracks, and uneven surfaces are filled.

Both parts to be glued must be clamped tightly so that the foam remains in place during drying.

Epoxy

Epoxy glue is a very strong two-component glue that is also ideal as a filler, because it is liquid and dries very quickly.

Epoxy glue is also widely used for the construction of wooden boats.

In woodworking, epoxy will be chosen over a polyurethane adhesive, if the load on the part will be high and extra strong bonding is required.

I wrote a more in-depth article on epoxy glue.
Go check it out to know all you need to know about using epoxy glue for your projects.

8 Awesome wood glue tricks

Tip 1 | Use salt

Do the two parts slide over each other through the used glue during clamping?

Prevent this by sprinkling salt over the glue after you have spread the glue over the workpieces.

The coarse grain of the salt keeps your workpieces in place better.

Be careful not to use too much salt.
According to glue specialists, salt can react with the glue and change the composition, resulting in a weakened connection.

Tip 2 | Spreading wood glue

To spread wood glue on your workpiece, you can buy different tools, such as rollers.

Use an old bank card or membership card to spread the glue.
The sides of these cards are perfectly straight and take away excess glue.

Moreover, these cards are easy to clean.
Just with a dry cloth and they are clean.

However, has the glue dried on the card?
No problem!
Because many of these cards are made of plastic, the glue will easily come off in 1 movement when it is completely dried out. 

Tip 3 | Cover clamps with wax paper/ foil

When wood glue comes into contact with steel bar clamps or pipe clamps, the moisture in the glue can cause the steel to leave a dark stain on your wood.

Or when you use homemade wooden clamps, the glue can cause the workpiece to get stuck to the clamp after the glue has dried.

To avoid this, place a sheet of wax paper or cling film over the clamps.

The protective layer will also catch glue drips, that would otherwise come over your clamps and workbench.

Simple and cheap!

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Tip 4 | Rub the joint

Do you want the guarantee of a strong adhesive bond?
Rub the boards over each other to evenly spread the glue before clamping.
By having the glue all over the surface, you are always sure of the best connection between the two pieces you want to connect.

Tip 5 | Tack before you clamp

Wood glue makes boards slippery and can make it difficult for you when applying clamps.
It is quite a task to keep the boards correctly aligned.
In addition to the solution of the salt that I have just discussed, you can prevent the wood from slipping with a few strategically placed brads. 
You can do this before applying the clamps.

Note, however, that the brads are visible with the finished product and do not use brads if you still have to cut into the wood.

Do you want to work with brads?
Lengthen your workpiece and place the brads at the end of your workpiece.
After the glue has dried, you can cut this piece so that no more brads are visible or present in the workpiece.

TIP:

If you consider buying a nail gun, be sure to watch my blog How to choose the right nail gun for your projects. A complete nail gun guide.
I have used my nail gun for almost every project since I bought it, so I can highly recommend buying one.

Tip 6 | Make woodfiller with woodglue

If your project has small cracks, you can make your own wood filler that matches the color of your project.

Mix some fine sawdust, that you can remove from the sander collection bag, with wood glue into a paste.

For best results, use sawdust of the same wood type as your project.

I wrote another article where I go deeper into wood fillers. Be sure to check out that article.

Tip 7 | Use tape

Painter’s tape is never far away from me when I use wood glue.

I use it in different situations.

Sometimes I use masking tape along both edges of the joint before gluing.
The excess glue will then end up on the tape and will not leave any stains on the wood.
I apply this trick when I use more expensive woods.

Another good trick with painter’s tape is when you need to glue corners.

Place the 2 boards with their 45-degrees cuts against each other.
Connect the 2 boards at the bottom with tape, place the wood glue on the 45-degree cuts, and then simply fold the 2 boards together until you got your 90-degree corner.

You can also use painter’s tape to keep newly glued pieces in the correct position.

For best results, use sawdust of the same wood type as your project.

Tip 8 | Thickening wood glue

As wood glue ages, it tends to thicken.
Because the glue is thicker, it is more difficult to use for gluing.

Many don’t know but you can thin this glue again.

Adding 1 or 2 drops of vinegar to the glue will make it easier to process.

However, be careful not to use too much vinegar because it can change the composition, resulting in a weakened connection.

How to store wood glue?

Most glue manufacturers provide their products with an official shelf life. The stated shelf life of wood glue is usually one to two years.
They use this shelf life to limit liability in the event that poor storage conditions cause product failure.

However, the expected shelf life of many types of glue is higher than those few years.
When you store wood glue under optimal conditions, it can last 10 years or more.

But what are those optimal conditions?

I list the most important for you:

  • Always keep the wood glue in the original packaging.
  • dry, cool cellar is the ideal place to store wood glues.
    You may be able to extend the life of your glue if you have room for it in your refrigerator.
    I can already hear you thinking: how will I explain that to my partner.
  • Do not try to freeze the glue.
    If it does happen, most wood adhesives are designed to withstand at least five freeze/thaw cycles.
    The glue forms, gels with each cycle. Mixing these gels will break these gels down again, but the gels will be more difficult to disperse with each subsequent freeze/thaw cycles.
  • Heat can also cause the polymer to clump and gel.

How do you know if your glue has gone bad?

You must be able to pour glue.
If the glue is stringy or tacky or wants to stick to itself rather than the wood, it’s probably past its peak.

FAQ

FAQ 1 | What does wood glue do?

Wood glue is an adhesive used to tightly bound pieces of wood together.
By penetrating the wood, the connection can become stronger than the wood itself.

FAQ 2 | What is the strongest glue for wood?

Polyurethane glue is one of the strongest types of wood glue.
It can be used for many different materials, such as wood, plastic, stone, metal, ceramic, foam, glass, and concrete.

FAQ 3 | Is wood glue waterproof when dry?

The “D” markings on the wood glue bottles indicate whether the wood glue is waterproof or not.
More info can be found in this blog under wood glue classes.

FAQ 4 | Does wood glue shrink?

Wood glues are around 50% solids and therefore shrink when they dry.
If there is a gap between the to workpieces, the adhesive will shrink when it dries.
It will pull away from one surface or the other, leaving gaps in the glue line.

FAQ 5 | Is PVA the same as wood glue?

PVA is a rubbery synthetic polymer with the formula (C4H6O2)n.
Polyvinyl acetate is a component of a widely used glue type, commonly referred to as wood glue, white glue, carpenter’s glue, school glue, or PVA glue.”

FAQ 6 | How long should wood glue dry before removing clamps?

For most of our wood glues, it is recommended clamping an unstressed joint for about an hour.
Stressed joints need to be clamped for 24 hours.

FAQ 7 | How long is wood glue good for?

As I already wrote in this blog, the shelf life of wood glue by the manufacturers is about 1 to 2 years.
However, wood glue can be stored for much longer under the right conditions.
Be sure to read the “How to store wood glue” section above for more information.

FAQ 8 | Should you sand wood before gluing?

Wood glues work by attaching to cellulose on the wood and the smoother (tighter) the joint, the less adhesive is needed to bond the surfaces.

FAQ 9 | Can you use too much wood glue?

Too much glue will slow down the curing process and you will spill a lot of expensive wood glue.
Make sure that the entire surface is covered with wood glue.
You know when you have used just enough wood glue when it is lightly pushed out over the full length of the joint.

FAQ 10 | What is the difference between white and yellow glue?

The yellow has a higher instant tack.
The yellow does not like to be moved once the pieces are joined. With yellow glues, there is a chemical reaction that occurs that cannot be reversed with the addition of moisture.

FAQ 11 | Is wood glue really stronger than wood?

Yes, the glue is stronger than the wood because it penetrates into the cells of the wood.
You can read more about this in this blog in the section “How does wood glue work?”

FAQ 12 | Can you sand wood glue?

Because the glue penetrates into the pores of the wood, wood glue cannot always be removed.
The only real solution is to sand them away.
In many cases, wood glue can be sanded off quite easily.
Sometimes it is possible to remove wood glue by softening it with acetone.

FAQ 13 | Does glue dry faster in hot or cold?

Because it is a water-based adhesive, it will dry faster if conditions are favorable for the evaporation of the moisture present.

In other words, in warm dry air, wood glue will dry faster than in colder air.

If it is extremely moist, it will slow down the evaporation of the water in the adhesive.

Wood glue also dries faster on porous materials, such as fabric and paper, because these materials allow the water to evaporate through them.


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