The Secrets to Fixing, Clamping, and Gluing Wood
With your joints fitting together nicely, the next step in your woodworking project is to glue everything up. Gluing wood sounds easy enough, but there are a few important things to take into consideration.
From choosing the best wood glue for your needs, to deciding whether you require additional fixings or not, each job has different requirements. It’s also essential to know how to properly clamp your wood together during the gluing stage. Doing it wrong can damage your workpiece and stress the joints. Meanwhile, if you apply wood glue incorrectly, you’ll make a mess that can be difficult to clean up.
With all that in mind, in this chapter, we’ll take a look at all you need to know about how to glue wood, as well as fixing, and clamping your work for an unbreakable finish.
Different Types of Wood Glues
There are several types of wood glue to choose from, each with different properties and uses. It’s important to use the right glue for the job to prevent mess and ensure a strong finish that will last. Here are some of the most common types of wood glue.
PVA glue, also known as white glue or carpenter’s glue, is one of the most well-known wood glues. Used in schools and professional workshops alike, it’s an affordable and easy-to-use general-purpose wood glue.
It boasts a ready-made emulsion of polyvinyl acetate (PVA), which is suspended in water. As the water is absorbed into the wood fibers or evaporates, the glue dries and sets, forming a strong bond. Standard PVA glue isn’t waterproof, but you can find exterior grade PVA glue that is. There’s also yellow PVA glue, which is slightly thicker and is resistant to heat and moisture.
In general, PVA glue dries well, is easy to apply with a putty knife or just by squirting into the joint, and it cleans up nicely as it sets clear. It’s an excellent wood glue for a wealth of tasks.
Polyurethane glue is waterproof and extremely strong. These glues are particularly good for gluing end grain. Water-based glues tend to penetrate wood fibers in the end grain, making them swell, then shrink as the water dries out. This can weaken the joint.
However, polyurethane glue expands as it dries. Once it has set, the glue won’t expand or shrink in any way. The glue cleans up well and can be sanded and stained without issue.
Polyurethane glue is a top choice for joints that aren’t quite as tight as you’d like, as the glue will expand to fill any gaps. Be advised that you’ll need proper clamping pressure to ensure the glue doesn’t push the joint apart as it expands.
Also known as cyanoacrylate (CA) glue, a tube of super glue can be handy to have around the workshop. It’s not the best choice for large joints though and is best suited to small elements.
It dries fast, ideal for quick repairs and intricate projects such as toy making. It can work well when repairing furniture and chips of wood that need to be fixed back in place. Instead of a clamp, such jobs work better with masking tape to hold the repair in place until the glue has set.
Hot Melt Adhesive (HMA)
HMA glue is typically available in the form of cylindrical sticks. These are fitted into a glue gun, then as the trigger is pulled and heat is applied, the glue melts and can be applied. It’s easy to use and sets pretty quickly, making it a good choice for jigs that need to be put together fast.
It’s also good for gluing other materials to wood, such as the carpet for a cat stand. HMA wood glue shouldn’t be used for joints though, particularly those that will take a lot of stress over time.
Another type of HMA glue is used in veneering. A thin sheet is laid between the veneer and the wood, then melted using a domestic iron. You can also find edging strips for plywood or chipboard that works in the same way.
Animal glue, such as liquid hide glue, is the traditional adhesive used by the woodworkers of yesteryear. Made from boiled animal collagen (skins and bones), it’s now not very often used in woodworking projects since better alternatives are available.
Animal glues are commonly available in granules that need to be dissolved in water, then heated in a special glue pot. Once set, the glue can be planed and sanded, but can be re-softened by applying heat, making them a poor choice for exterior jobs in hot climates.
Modern liquid hide glue is also ready to use from the tube and does come with a number of advantages. It sets hard and brittle, providing an extremely strong fix. However, it can also be broken relatively easily. With a chisel and a firm hit from the hammer, the glue breaks, releasing the two pieces of wood, which remain fully intact and undisturbed by the glue.
This wouldn’t be possible with many modern types of wood glue, which is a major boon for violin makers, who must dismantle the instruments from time to time to carry out repairs. It can also be handy for furniture makers.
How to Glue Wood Together Properly in 4 Easy Steps
Knowing how to glue wood is an essential skill for any woodworker. Fortunately, with a few pointers, it’s not too difficult. For the best results, preparation is key, as well as choosing the correct wood glue for the job. Follow these four steps and you can’t go wrong.
1. Prepare the Surfaces
To ensure success when gluing wood, make sure the surfaces are properly prepared before you apply the glue. You need clean, smooth, flat, and grease-free surfaces when you glue wood together, so don’t be tempted to rough them up at all!
2. Check Moisture Content
This early check should be done before you start, but it’s worth mentioning. The more moisture there is in the wood, the lower the quality of the finished joint. Some glues simply won’t set properly if the wood has a moisture content of more than 20%.
On the other hand, make sure your wood isn’t too dry. Timber with a moisture content of less than 5% will often soak up the glue too quickly (especially PVA and other water-based glues), providing a less-than-satisfactory joint.
The most important thing is to ensure all the components that will be glued are covered adequately. Unless otherwise stated by the wood glue manufacturer, it’s best to apply a layer of glue to each part of the joint. Don’t use too much glue, and use a glue brush, putty knife, or even a stick, to spread it evenly. For larger surfaces, you can also use a rubber roller to apply the wood glue.
Take care with mortise and tenon and bridle joints, as the tenon section will often have the glue scraped off as it’s inserted. To remedy this, apply a good amount of glue around the inside edge of the mortise. This way, as the tenon goes in, it’ll drag the glue from the mortise in with it, providing a strong fit.
4. Clamp the Joint
The majority of joints need to be clamped while the wood glue dries. Don’t clamp directly onto your workpiece. Instead, place some scrap wood between the clamp and the wood edges to prevent the clamps from denting or staining the wood.
Place the clamps at the joints and tighten them up, ensuring the joints are closed up nicely. Don’t over-tighten the clamps, as this can cause the wood to bow, but be sure to tighten each clamp evenly. Avoid using too many clamps, one at each joint is generally enough for frames.
After clamping, check the joint and wipe away any excess glue that has been squeezed out with a damp cloth, making sure to check both sides. Sash, or steel bar, clamps are the best for frames, while a C-clamp is great for gluing two pieces of wood together face to face.
How to Glue and Clamp Edge-to-Edge Joints
Edge-to-edge joints require a little extra attention. It’s important that you take care when clamping your boards together for gluing. You will need at least three large sash clamps to do the job, two near the end and one in the center. For larger projects, you may need more.
It’s always best to clamp your board dry before applying glue. This allows you to make sure all the joints are flush, square, and straight. Once you’re happy, apply a thin layer of carpenter’s glue on each jointing edge. Place the first two clamps across the boards and each end of the board. Check for steps, and if any boards aren’t flush, gently tap them down with a mallet and block.
Now turn the board over and apply the third clamp across the middle of the panel. This pulls the joints tight at the center of the panel but also prevents the boards from bowing. Wipe away any excess glue, checking that everything is flush, then leave it clamped up until the glue has set.
You can avoid stressing out about steps and boards not being exactly flush, by making your panel a little thicker than it will finish. Once the glue has set, you can then plane it down flat.
Important Woodworking Fixings
Gluing wood is perhaps the most common way to keep your joints together, but it’s not the only one. Other fixings, most notably nails and screws, are available and come in very handy, especially if you’re building something that might need to come apart again one day.
With the correct wood screws, you can create an extremely strong joint that is easy to dismantle. Besides holding joints together, screws are also commonly used to attach hinges, handles, and other fittings to your DIY projects.
Wood screws come in several variations, depending on the following elements:
- Head type: There are three main types of wood screw heads; countersink, raised, and round. Countersink heads finish flush with the surface of the wood, with a tapered recess for the head to sit in. Raised heads have the same taper, but a domed top leaves the head exposed. Meanwhile, a round head has a flat bottom and a domed top, mostly used for fixing flat sheet material to a wooden surface.
- Screw slot: Traditional screws had a single straight slot across the center of the head. Nowadays, cross-head or Phillips head screws are more common, featuring a crossed slot that is self-centering. You’ll find other types on the market too, with the Pozidriv perhaps the most common. This is similar to Phillips but has a further four notches in the center of the screw head for improved grip.
- Length: Wood screws typically range in length from 1/4″ to 6″, though you’ll find longer and shorter types. When choosing the correct length, select a screw that is about three times longer than the thickness of the material you’re fixing. Be sure that it will also finish at least 1/8″ short of the other surface to prevent the fibers from bulging out.
- Gauge: The gauge of a screw refers to its diameter, ranging from 0 – 20, roughly 1/16″ to 5/16″. Thicker screws provide a stronger fix but can split the wood if pilot holes aren’t drilled.
- Material: Most general-purpose wood screws are made from steel. However, you can also find decorative brass screws and stainless steel screws for exterior use. You’ll also find coated steel screws for a variety of uses.
All wood screws have a shank, a part of the screw without a thread. This design pulls the joint together as the screw is tightened while preventing the screw from overheating and breaking.
Never Use Drywall Screws for Wooden Joints
At first glance, screws all look the same, so you might simply pick up the cheapest bag from your local hardware store. However, drywall screws are threaded the full length which can force two pieces of wood apart when you’re trying to screw them together. Invest in proper wood screws for a better finish.
Nails and Pins
Nails and pins aren’t used as widely as they once were but are still handy to have around. You’ll find plenty to choose from, ranging in length and gauge, as well as head type. Large (up to 6″), round-headed nails are often used in rough carpentry constructions and frames.
Smaller panel pins are great for securing small joints and fixing things like decorative beads to window frames. Tacks with large, flat, round heads, meanwhile, are ideal for attaching fabric to an upholstered frame.
Pins can be driven below the surface of the wood using a nail punch and hammer, and the holes filled in to hide them entirely.
With your joints glued and fixed together, it’s time to start cleaning up your work and getting it ready to decorate. In the next chapter, we’ll take a look at sanding, scraping, and filing wood to ensure a beautiful finish.