Wood glue is often advertised as being stronger than the wood they join. But is that really true? Wood glues have become stronger and stronger in the past ten years and we have come to a point where a lot of carpenters just stopped using wooden joints when gluing wood together because the bond that the wood glue creates is strong enough so that wooden joints aren´t needed as much anymore.
As a whole, wood glue is stronger than wood. Most types of wood can withstand a force between 1000 PSI (Pounds per square inch) and 200 PSI while most wood glues withstand between 3000 PSI and 4000 PSI. If a glued joint breaks it´s the wood that gave in most of the time and not the glue.
So as you can see, wood glues are indeed stronger than wood. But that doesn´t mean that simply glueing wood is necessarily the best way to join two pieces of wood. There are a few things that can strengthen a glued connection and ensure that the wood won´t break as easily when put under stress.
The Strongest Glue for Wood
There are quite a few different types of glue that can be used to glue wood. The most well-known glue is probably PVA glue. It´s also known as regular wood glue or white glue. But it may come as a surprise to you that PVA glue isn´t the strongest glue that can be used to glue wood.
In total, the strongest glue for wood is two-part epoxy with a strength of between 3000 PSI (Pounds per square inch) and 4000 PSI. PVA glue can generally have a strength of up to 3800 PSI and Polyurethane glue can have a strength of up to 3900 PSI.
But you should not simply choose the strongest glue for every single one of your projects simply because it is the strongest glue. Depending on your project simple PVA glue might be more than enough.
Epoxy resin is actually the worst choice for gluing most wooden projects even though it is the strongest glue.
The Different Types of Glue for Wood
There are a bunch of different kinds of glues that you can use for gluing wood but the three most used types are PVA glue, Polyurethane, and two-part Epoxy.
It really depends on your project what kind of glue is best for you. I will quickly go over all three of these glues so that you can choose for yourself which one is best for your specific project.
When to Use PVA to Glue Wood
PVA glue (also knows as regular wood glue or white glue) is probably the most often used glue for joining wood together.
It is easy to apply and use and it is very strong!
Regular PVA glue has an average strength of around 3000 PSI while stronger PVA glues can be as strong as 4000 PSI.
PVA glue is the go-to glue for gluing wood. There are a lot of different PVA glues from water-resistant over quick dring to extremely strong ones. I usually use regular wood glue for most of my projects and only use water-resistant glue for outdoor projects.
I usually use Gorilla wood glue for outdoor projects and Elmer’s wood glue for indoor projects. Gorilla wood glue is also quite a bit stronger than Elmer’s glue so I tend to use it for some projects where I need a stronger bond but usually, Elmer’s glue is just fine.
When to use Polyurethane Glue to Glue Wood
Polyurethane is another very popular wood glue. It is very strong with around 3500 PSI and stronger versions with 4000 PSI.
It is also very easy to use and while it dries quicker than wood glue its initial strength isn´t as good. Polyurethane glue is also quite a bit more expensive.
I usually only use it very rarely for gluing wood. When I use it then usually to glue smaller pieces of wood or if I want to glue wood to another material. But even then I usually tend to use two-part epoxy more often than polyurethane.
One big advantage that Polyurethane glue has over most wood glues is its water resistance. This is why it is used mostly for outdoor projects.
You can get Polyurethane glue at your local hardware shop or right here on Amazon.
When to Use Two-Part Epoxy to Glue Wood
Two-part epoxy is probably one of the strongest glues out there. It adheres to practically anything and its strength is around 4000 PSI on average.
I personally love to use epoxy resin for projects where I need to glue something that has to survive a lot of stress. Two-part epoxy will survive almost anything but it has one big weakness.
Two-part epoxy dries completely rigid meaning it will not stretch, bend, or move with the material. This can be a problem if you glue wood with it because wood tends to move. So the glued parts could come apart after a while if the material moves too much.
Two-part epoxy is also slightly toxic while it dries so it should only be used in a well-ventilated area!
I personally recommend using Epoxy glue from Gorilla. It dries fast and creates a very strong bond. You can buy it at your local hardware store or right here on Amazon.
How to Apply Wood Glue Properly
Wood glue is very strong but only if it is applied properly. There are a few things that you have to keep in mind when using wood glue.
Before we start with gluing or preparing the surface for the glue application we first have to take a quick look at the surfaces that wood glue can and can´t glue.
For one, wood glue can´t glue wooden surfaces that have been sealed with a topcoat. Wood glue needs to be able to be absorbed, at least partially, by the fibers of the wood in order to stick to it. The only exception here is a two-part epoxy, that will stick to anything, and in some cases, depending on the topcoat, Polyurethane.
But generally, gluing already sealed wood is not a good idea without roughing up the topcoat by sanding it with some fine-grit sandpaper.
Wood glue also has a hard time gluing already painted to stained wood. It is generally not recommended to glue stained or painted wood without sanding the surface first. Polyurethane and two-part epoxy, however, can be used to glue painted or stained wood together without any issues.
But I would still not recommend gluing painted or stained wood without sanding it first.
Now that we have that out of the way let´s take a look at how to prepare and apply wood glue properly.
Clean the Surface
First off, clean the surface properly! It is only important to clean the surface from dirt and debris. If the surface only has some wood dust on it then you could actually leave it be and simply apply the glue if you wanted to but I personally still clean every piece of wood that I glue.
Most of the time it is enough to wipe any dust or debris away with a dry towel before you apply the glue. I usually have a dry brush laying around that I use to clean my wood.
Apply the Glue
This is where I see a lot of people go wrong. You don´t have to apply a lot of wood glue to the surface.
More glue does not equal stronger adhesion!
It is more than enough if you apply a thin film on top of the whole surface. I usually spread a few bigger drops of glue over the whole surface and then I use a scrap piece of wood to spread the glue evenly.
Then I wipe the excess away and do the same for the other piece.
You have to work quite fast or the glue will start to dry. So right after you applied the glue press both pieces together and then continue to clamp them together.
Clamp the Pieces Together
Everyone who works with wood knows that you can never have enough clamps! Clamping a complex piece of work together for drying is an art form in itself.
I usually plan how I go about clamping the piece before I apply any glue to the piece. You can use other pieces of wood or sheets of wood to clamp your project together. You can really use anything you like.
Just make sure that the project is clamped properly and that it can´t fall off the workbench while it dries.
Also make sure that the clamps, that you are using, do not damage the pieces that you work on. You can either put a piece of cloth or a piece of wood under the clamps to protect your project from any scratches or dents.
Wood glue should be left to dry overnight, depending on the brand.
How Long Does Wood Glue Last?
A lot of people keep asking me how long their newly build project lasts if they only glue it and don´t use any screws and my answer is pretty much always the same. It depends.
As a whole, projects build with wood glue can last decades. It depends on how much exposure to the elements the project has and how well it was build but wood glue has the potential to last decades. The shelflife of wood glue, on the other hand, is about two years maybe ten when it is stored in optimal conditions.
So you really don´t have to worry about wood glue loosing it´s strength over the years. Wood glue will adhere wood for a very long time without the need to reapply it any time soon.
I had some old wooden wardrobes that were 90 years old that I disassembled and the glue still held them together insanely well.
But wood is a material that moves, so if you use a type of wood that moves a lot or if your project is exposed to the elements then that will weaken the wood glue over the years. So in the end, it really depends on the project and how well it was built.
Wood joints will further strengthen the connection. So if you are worried about the longevity of your project then you can use wood joints to ensure that your project will survive for a long time.
Is Wood Glue Stronger Than Screws?
An interesting question that I get asked a lot. It is almost like an age-old discussion among Hobbyists that no one seems to answer sufficiently.
As a whole, wood glue is stronger than screws especially if wood glue is used together with wood joints. Screws have one big advantage over wood glue and that is speed. It´s easier and faster to simply use screws but the connection will still be stronger when wood glue is used to join wood.
The biggest reason why screws aren´t as good as wood glue is that screws don´t tend to move with the wood when it moves. So screws will loosen after a while. They could even break when under too much stress.
Wood glue, on the other hand, is quite elastic and generally tends to move with the wood when it expands or contracts.
Wood glue works especially well when two surfaces with a lot of surface area are joined.
Can You Use Wood Glue for a Table Top?
It is a little hard to imagine how strong wood glue has become in the last 10 years. That´s probably also the reason why I get asked repeatedly if you can glue this or that with wood glue and if the glue is really strong enough.
As a general rule, wood glue is strong enough for a table top and wood glue can be used to glue a table top to its base but it is recommended to use some sort of joint to ensure that enough surface area is present for the glue to form a strong bond.
Generally, you want to make sure that the base has enough surface area that the table top can properly adhere to. This can be done by using joints, or by using a wide base.
Then you also want to make sure that you apply enough pressure to the pieces after applying the glue to make sure that they adhere properly to one another.
And that´s pretty much it. Gluing a table top to a base is almost exactly the same process as gluing any other two pieces of wood together just on another scale.