Plain Old Wood Glue is Best
Dozens of glues claim to work well on wood and a variety of other materials. But regular wood glue is the best choice for raw wood-to-wood joinery. Most wood glues are a type of polyvinyl acetate (PVA). Also sometimes called carpenter's glue, wood glue is formulated to penetrate wood fibers, making glue joints that are stronger than the wood itself.
Wood Glue Can Last for Years
You may have heard that PVA glue goes bad after freezing or sitting around for a long time, but the truth is that it might still be OK. Try stirring it with a stick to mix all the glue particles (don't just shake it). If it's a little thick, add some water?up to 5 percent. If glue flows freely from the bottle and feels slippery between your fingers?not stringy or clumpy?it's probably OK to use. But if in doubt, throw it out. It's not worth taking the chance.
Use Waterproof Glue for Outdoor Projects
If your carpentry project might get wet, use glue that stands up to water. Glues labeled 'water resistant' are fine for things that'll only get wet occasionally. For most outdoor projects, however, choose 'waterproof' glue, which comes in both PVA and polyurethane formulas. Both types are plenty strong and stand up to the weather, but polyurethane glue has the added benefit of being able to bond materials like stone, metal and glass. It's messy stuff, though, so wear gloves while using it.
Mask Glue Joints Before Prefinishing
Finishing the parts of your project before you assemble them can be a great time-saver and allow you to get a better-quality finish. But for a strong glue joint, you have to keep the joints free of finish (glue doesn't stick to varnish or stains very well). The solution is to apply masking tape to the surfaces that will be glued. Then remove it to expose raw wood when you glue up the project. Any good-quality masking tape will work. If you'll be using a water-based finish, you'll get the best results with a “no-bleed” tape such as green Frog Tape and ScotchBlue painter's tape.
Apply Wood Glue With a Flux Brush
Flux brushes, available in the plumbing department of hardware stores and home centers, are just right for applying and spreading glue. They work especially well for gluing intricate joints like the ones in the coped door rail shown here. You can store a wet brush for a few days in water and then wash and use it over and over again.
Cover Bar Clamps With Wax Paper
When you use steel bar clamps or pipe clamps, and wood glue comes in contact with the clamp, the moisture in the glue can cause the steel to leave a dark mark on your wood. Lay a sheet of wax paper over the clamps to prevent this “dark spot” problem. It will also catch glue drips that would otherwise get all over your clamps and workbench.
Rub the Joint
One good way to ensure a strong glue joint is to use the 'rub joint' method. Simply apply glue to the edges of one or both boards and rub them together to help spread the glue evenly before clamping.
Add One Board at a Time
When you're gluing several boards together, it can be difficult to get all the top surfaces perfectly aligned. Here's a tip that solves the problem. Rather than glue and clamp all the boards at once, add one board at a time. Let the glue joint set for about 20 to 30 minutes, then release the clamps and add another board. This method will take a little longer. But it makes it a lot easier to keep all of the boards' top surfaces flush, which makes for much easier flattening and sanding of the surface.
Attach Small Pieces With Superglue
Of course you reach for a superglue (cyanocacrylate glue, or CA) to fix a broken teacup handle. But did you know that it works on wood, too? In fact, CA glue is really handy for attaching small trim pieces that would be hard to clamp. Just put three or four drops onto the parts and stick them together. We like the gel version of CA glue because it doesn't run off and make a mess.
Spread Glue With a Notched Trowel
When you're gluing large surfaces, an inexpensive notched plastic trowel works great for spreading the glue. To find one, look in the flooring or tile section of the hardware store or home center. If you're fortunate enough to have a pair of “pinking” shears in the family sewing basket, you can make our own spreader from an expired credit card.
Water Finds Hidden Glue
Once squeezed-out glue has been removed, there's still a chance that some is hiding. And if you don't find it now, you'll see it later when you apply stain or finish. Spray some warm water near glue joints to make hidden glue more visible. The water will also soften the dried glue, making it easier to scrape off.
Let It Jell, Then Shave It Off
Look at any woodworkers' forum and you'll likely find a debate about the best way to remove glue squeeze-out. Some woodworkers insist that you should clean it up immediately with a damp rag. Others let it dry completely, then scrape it off. We think that in most cases the best method is to wait about 30 to 60 minutes—just until the glue turns a darker color and changes to a gel—and then shave it off with a sharp chisel. This will remove almost all of the glue without making a mess. You may still have a little cleanup to do, but it's a lot less work than cleaning up wet glue or removing hard glue.
Remove Excess Glue With an Abrasive Pad
It can be difficult to remove excess glue with a rag. And if you don't get it all off the surface when it's wet, the dried glue can show up as light spots when you finish your project. But a synthetic abrasive pad, dampened with water, works perfectly to remove the glue. Dip the pad in a container of water. Unlike a rag, which is hard to rinse glue from, the pad has a loose synthetic weave that releases glue easily. After rinsing out the pad, shake it to remove most of the water. Then use it to scrub off excess glue. When you're done, dry the surface with a clean rag. Green abrasive pads are found with the cleaning supplies at grocery stores, hardware stores and home centers.
Remove Hardened Glue With a Paint Scraper
We've all been there. You glue up your project and then quit for the night. The next day you discover the rock-hard glue and realize that you forgot to scrape off the glue squeeze-out. Don't despair. A sharp paint scraper makes fast work of hardened glue. Either a sharp steel scraper or, better yet, a carbide paint scraper will pop off all those glue beads in a heartbeat.
Tack, Then Clamp
Wood glue makes boards slippery, so it can be hard to keep them lined up correctly while you apply clamps. An easy solution is to hold the parts in alignment with a few strategically placed brads before you apply the clamps. For leg glue-ups like we show here, cut your parts extra long and place the brads where they'll get cut off during the finishing process. Otherwise, just place brads where the filled holes won't be too visible.
The Right Amount of Glue
With a little experience, you'll develop a feel for how much glue is just enough. Too little glue creates a “starved joint,” which will be weak. Too much glue makes a mess and wastes glue. With practice, you'll know just how much to apply. You should see a continuous line of small glue beads. When this perfect glue joint sets a little, you'll find it easy to scrape off the jelled excess, and you'll have very little cleanup to do.
Picking the Best Exterior Glue
An exterior-grade yellow woodworking glue may work fine, especially if it's protected by a coat of paint or somewhere out of the rain. However, for joints that get a lot of weather, use polyurethane glue; it's fully waterproof and bonds wood and other materials well. It's not gap-filling, so be sure to get a good fit and clamp it.
Apply Tape to Control Glue Squeeze-Out
Glue squeeze-out soaks into the fibers of raw wood, leaving blemishes when you later apply the finish.The usual solution for this is to clean it off with a wet rag or sponge. But too much water around the joint can weaken the bond. It's better to stick down masking tape along both edges of the joint before gluing.The excess glue will then squeeze out onto the tape instead of the wood, and you can just peel the glue away when it's dry.
Glue + Sawdust = Wood Filler
When you need wood filler that matches the color of your project, mix some fine sawdust and glue together until it forms a paste, which you can use to fill small gaps and cracks. For best results, use sawdust from the same species of wood as your project; you can get some from the bag on your electric sander. Just don't try this trick for large gaps or patches?they'll stick out like a sore thumb.
Avoid Sunken Joints
PVA glue has lots of water in it, and that water will cause the wood edges at glue joints to swell. If you plane or sand glued-up panels too soon, you could be left with sunken joints after the wood dries and shrinks to its original state. Most water-based glues reach full cure in about 24 hours, but it can take several days for swollen glue joints to shrink back to size. If you're gluing up a fine piece of furniture that you hope will become a family heirloom, wait a few days after gluing up your project before sanding or planing.
Slow-Setting Glue Buys You Time
Most wood glues set up quickly, which can be a blessing or a curse. Sometimes you want a quick bond, but on a complicated glue-up, you might want more time before the glue starts to set up. Slow-setting glues have labels that say 'longer assembly time' or 'longer open time.'