Nails and screws are generally consider the best for construction projects, from furniture to building homes. You may have not even thought about using wood glue instead of screws. However, it turns out that if you aren’t using wood glue, you may be making a mistake.
Wood Glue and Screw Basics
Before we learn which is stronger, let’s learn a bit more about our contenders, wood glue and screws.
There are several types of wood glue. PVA glue, or Polyvinyl acetate, is the most common type of wood glue. It’s also known as carpentry glue, and is ideal for most wood projects.
Hide glue is made from animal products. It typically needs to be heated and applied with a brush. As the glue cools, it dries and forms the bond.
Epoxy is one of the strongest types of wood glue. It typically takes longer to cure, but creates a very secure bond. It has two components, a resin and hardener. The two are mixed together, and then applied. When epoxy dries, it’s waterproof and very strong.
Polyurethane glues are activated by water. They create a strong bond as well.
There are a seemingly endless list of screw types. Even narrowing down the list to wood screws leaves a dizzying array of choices.
Hardened steel screws are the most popular choice for indoor woodworking projects. They are also known as production screws, construction screws, multipurpose screws. They don’t require predrilled pilot holes. They are strong enough to use on any type of wood, and are even ideal for some metal projects.
However, they aren’t designed for outdoor use. If you are working on an outdoor project, you should go with deck screws. These are essentially production screws with a coating that makes them weather resistant.
Which is Stronger?
It turns out that when used correctly, wood glue is stronger than screws. It’s even stronger than the wood itself.
One experiment performed by Geekpub measured the amount of force necessary to break the bond of wood glue and screws.
They created two sets of two boards with an overlap of 12 inches. The wood glue was allowed to cure for 2 weeks, even though 24 hours is the recommended cure time.
One set of boards used 2 screws to attach them together. The last set used 4 screws. All the boards were the same length. The screws were 3 inches long, and holes were predrilled to avoid stressing the screws.
The test revealed that the screws failed before the wood glue. The board attached with 2 screws failed at 442 pounds of pressure. The boards with 4 screws failed at 520 pounds of pressure.
The first set of boards attached with wood glue failed at 520 pounds. This set had a knot in the wood, which is believed to cause it to fail under less pressure. The second set of boards failed at 590 pounds of pressure.
They also used a control board. This board had not been bonded. It broke at 592 pounds of pressure, essentially the same as the set of glued boards.
Why is Glue Stronger Than Screws?
Glue is stronger than screws because it bonds together a larger surface area. Glue bonds two pieces of wood across a large area. Screws can also connect the two boards in a small area.
In the case of the glue, the boards themselves actually failed, instead of the glue itself. When screws are used, it’s the screws that fail.
Choosing the Right “Tool” for the Job
Whether you choose to use wood glue, screws, or a combination of the two, be sure that you choose the right type for the job you are doing.
Consider whether it needs to be weatherproof, how much weight it will be subjected to, the type of wood, and how much the joint will expand and contract.
Choosing the correct type for your project is arguably more important than the choice between wood glue or screws itself.
When to Use Wood Glue?
Since wood glue is stronger, there are many situations when it’s the perfect choice for your project. It’s ideal for joining most types of joint together.
It’s also ideal if you are attaching a medium to large surface area.
If you are concerned about attractiveness, wood glue is an easy way to prevent unsightly screws in your finished project. Sure, you can use a counterbore, but glue can be an easier way to avoid visible screws.
Lastly, you can choose wood glue for repairs. If a piece of wood has broken off, wood glue is the perfect way to reaffix it.
When Not to Use Wood Glue?
There are situations where wood glue isn’t a great choice.
Wood glue is excellent for most joints, including dovetail and finger joints. Butt joints, however, don’t have a large surface area. Wood glue alone isn’t always enough to hold these joints.
If the piece won’t need to support a lot of weight, wood glue alone can do the trick. However, if you are building a bench, large table, or bookshelf, you’ll want to use both screws and wood glue for these joints.
Another situation where wood glue isn’t a good idea is if you may need to disassemble the piece. Remember, wood glue is forever. Once you attach two pieces with the adhesive, they will not come apart again. If you need to disassemble it at some point, wood glue isn’t a good choice.
Beds are a great example of this. They are typically brought into the bedroom, and then assembled. If you use wood glue to assemble your bed, it will likely need to stay with the house if you ever leave, unless you intend to cut it into pieces.
Wood expands and contracts over time due to temperature and moisture. This creates movement. Wood glue is designed to be very rigid. This means it doesn’t allow the pieces of wood you’ve attached together to move.
Drawer bottoms and table tops are excellent examples of this. They should be designed to expand and contract, which they can’t do if they are glued. This puts stress on the wood, which can cause buckling or cracking over time.
Wood glue works well when you are joining two even surfaces. If the surfaces are uneven, the bond will not work well. Wood glue is designed to be applied in a thin layer. As the two pieces come together, the glue bonds with both surfaces, creating a secure hold.
If there are gaps or uneven surfaces, you’ll need to use screws. Screws have the added advantage of pulling the two pieces together, which can help reduce gaps.
When to Use Screws and Wood Glue?
Experts are divided on whether you should ever use screws and wood glue to secure the same joint. Some claim that this can create a stronger bond than either of them alone. Others believe that the screws can disrupt the glue, and that they shouldn’t be used together.
There are a few situations where wood glue and screws are commonly recommended, however.
As mentioned earlier, butt joints can be secured with wood glue and screws. Of course, you can also simply use screws, and skip the wood glue, unless the joint will be under a lot of stress. In this case, it’s best to apply the wood glue, and then insert the screws.
Stripped screws are one of the most frustrating aspects of wood working. The combination of a screw and wood glue is the perfect fix. Once the stripped out screw is removed, the hole will be a bit bigger than necessary.
Instead of grabbing a larger screw, and risking splitting the wood, apply wood glue to the hole. Then insert a new screw. This will help secure the new screw, and fill in any slight gaps in the hole.
Considering Cure Time
Wood glue may seem faster than screws. After all, you simply brush the glue on, and allow it to dry. However, in the long run, it is often a slower process than screws.
When you use screws, the bond is instant. You can then move on to the next part of the project, without concern about the bond holding. You don’t have to worry about keeping the bond secure until it dries, either.
Wood glue is typically secured with clamps until it dries. Most types are secure enough to remove the clamps within an hour. However, you should wait 24 hours before putting pressure on the bond. This can make construction a much slower project with wood glue than it is with screws.