Before I began my woodworking project late last year, I knew I had to find a strong joinery technique that would ensure the longevity and durability of the finished product. I have always used screws and rivets to join wood, metal, and other substrates. In this project, I did not want to drill any holes as they would destroy the ultimate vision I had for my project. As such, I began looking into wood glue and whether it would work on metal.
You can glue wood and metal together, although it is harder to form a permanent bond. Epoxy and polyurethane glue are the best types to use, as they form the strongest bond between the two materials. If you don’t mind drilling holes, screws are the best option for attaching metal and wood.
Generally, wood glue is an effective substance that allows two wooden materials to bond without creating annoying holes or gaps. Given that there are so many available options on the market, it is essential to find the ideal product, especially if you want to bond two different substrates. So, without further ado, let’s delve deeper into what wood glue is, how it works, and if it works on metal.
What is Wood Glue, and How Does it Work?
Modern wood glue products are among the strongest adhesives available on the market today. Often, they are more powerful than wood itself since the glue provides a tight bond that lasts for many years. Wood glue is relatively versatile as it allows you to glue all sorts of materials together. From wood to metal to porcelain, you can rest assured that wood glue will improve the quality of the connections on your project and make it look better.
Generally, wood glue is an intriguing substance. When wet, it is available in liquid form, meaning it is easy to spread thinly and move around. Alternatively, when in solid form, it is difficult to remove and very hard. So when you apply a layer of glue between two surfaces that you want to stick together, the wet wood glue penetrates the most exterior layer of the substrates involved.
As it begins to dry, the wood glue starts becoming hard. Eventually, it dries to form a solid material that resides inside and between both substrates simultaneously. Due to the strong nature of wood glue, these two pieces hold onto each other tightly to make one solid piece.
Types of Wood Glue
As mentioned earlier, there numerous wood glue products in the market. Each of them consists of different bonding agents or chemicals, adhesive strengths, and viscosity or thickness. Thus, it is vital to know precisely what you are looking for before making a purchase.
One of the most vital considerations to make when choosing the right type of wood glue is its chemical bonding agents that allow the joinery of the product. With this in mind, let us look at the five main types of wood glue available on the market.
1. Polyvinyl Acetate (PVA) Glue
If you are familiar with carpentry, craftsmanship, or woodworking in general, you are likely to have heard about PVA glue. Polyvinyl Acetate is a rubbery synthetic that is colorless, odorless, and non-toxic on the skin. However, it is known to cause harm when consumed.
Available in yellow and white, PVA glue is a highly soluble substance that creates permanent and flexible bonds. While you can use this product on a wide variety of products, yellow PVA, popularly known as carpenter’s glue, is perfect for outdoor use and white PVA is most suitable for indoor use. Although this glue is robust and durable, it is also worth noting that it does leave behind a residue and does not work well on wood stains.
2. Cyanoacrylate (CA) Glue
Often referred to as crazy or super glue, CA glue is a temporary and quick-drying acrylic resin wood glue used for short-term projects. Although it creates hard and tight bonds, the glue does not penetrate the topmost fibers of the wood. As a matter of fact, it lies on the surface, making it more suitable for providing a short-term fix as you search for a permanent solution.
Additionally, cyanoacrylate glue is best for filling in holes or cracks with sawdust or as a reinforcement. This is the only type of wood glue that does not work well with dry boards and has a short lifespan of one month after opening the tube. Due to its adhesive strength and instant bonding nature at wood temperature, users must wear protective masks and gloves while using this glue.
If the glue gets into contact with your skin, the best way to remove it is by using nail polish remover or a small amount of acetone. It is also worth noting that this glue shatters upon dropping or hitting, thanks to its rigid and brittle bonds.
3. Polyurethane Glue
Polyurethane is a long-lasting plastic resin designed to form flexible bonds, especially when joining wood grains end to end. It is one of the most durable and potent types of wood glue available on the market. Polyurethane glue is also relatively versatile as it can join different materials, like wood, metal, plastic, foam, ceramic, concrete, stone, and glass. It can also be used for natural wood composites and softwoods, as it dries and leaves a natural wood color.
Moisture activates and expands polyurethane-based wood glues, allowing them to swell up and dry relatively quickly. Upon drying, this type of glue is tough and waterproof. However, it can be challenging to get a smooth finish after using this glue as it requires a certain level of woodworking experience and expertise.
4. Hide Glue
As its name implies, hide glue comes from the hides of animal skins and has been in use for many centuries. Generally, there are two types of hide glue; liquid hide glue and hot hide glue. Liquid hide glue is available in a bottle and is relatively easy to use. Unlike hot hide glue, users do not need to prepare liquid hide glue before use. Many people prefer using liquid hide glue as it does not damage any finishes on your project.
Alternatively, you must heat several granules of hide glue with boiling water in a pot before it is ready for use. The heat allows it to melt and liquefy, making it ready to use. Often, it is advisable to apply hot hide glue with a brush as it is more efficient. As the glue cools, it becomes solid and joins two substrates together.
5. Epoxy Glue
Available in two parts; resin and hardener, epoxy glue is a solid and waterproof adhesive that also serves as an effective filler. Both parts of this glue come in liquid form, and when combined, they form a chemical reaction, causing the glue to harden. Depending on the type of materials you are sticking together, the curing time of this glue varies.
As a general rule of thumb, the longer it takes for the epoxy glue to cure, the tighter the bond becomes. So, the more patient you are, the better the results. Additionally, you can use this glue even on two materials that do not match perfectly.
How to Apply Wood Glue to Metal
Wood glue is very simple to use. However, when sticking metal to wood using wood glue, you should make several considerations. Due to the difference in these two substrates, it can be tricky to join them together permanently. Luckily, polyurethane-based and epoxy glues are more than up for the task. Additionally, the bond created is often more robust than the wood itself.
Before applying the glue, you have to ensure that the surfaces are smooth, clean, and dry. You also have to ensure that all the tools you need are in close proximity to avoid wasting time before the glue cures. Brush any rough points in the wood surface and sand the metal’s surface, if necessary.
If you use polyurethane-based glues, you can fill it up in a caulking gun to ensure easy application. Alternatively, if you use the two-part epoxy glue, mix two equal portions of the two parts thoroughly on a disposable container or surface. Apply the mixture on the surfaces evenly. Since the glue takes approximately 5-10 minutes to set, you have sufficient time to adjust the surfaces to the best position.
You can opt to roll or use holding clamps on the surfaces to apply pressure and create a tighter bond. If you choose to roll, you can use a regular paint roller over the surface repeatedly. On the other hand, using holding clamps will aid in sanding down excess parts and apply other substances to the project before it dries. Once you finish applying the wood glue, leave the project in a cool and dry room. You could also leave the project in front of one or two high-powered fans to facilitate faster curing.
Frequently Asked Questions (FAQ)
Can you use super glue on metal and wood?
Yes. Super glue is another popular option for joining metal and wood. It sets quickly and can fix a range of items. However, you have to ensure that both surfaces are dry and clean to assure strong bonding.
Which is the best type of glue to use on metal and wood?
Many professional carpenters prefer using two-part epoxy glues as they provide strong and durable bonds. The glue also allows you to continue working on the task at hand after setting.