Mark Palma takes a look at what’s on offer and what products will work best for your needs
Going to the store and buying glue is a daunting task. I walk down that aisle and just stare. They all claim to be the perfect adhesive and will glue pixie dust, unicorn hide and anything in between. Having experienced sticky messes, glues that didn’t dry or pieces that fell apart under the weight of gravity I am now sceptical of the package claims. More than once I just grabbed the same brand I always do and crossed my fingers that I made the right choice. So let’s see if we can add a couple of adhesives to our ‘toolbox’ that let us achieve a better outcome when we try to join two surfaces together.
PVA adhesive
What we often think of as ‘yellow wood glue’ is an incredibly versatile adhesive. For most wood joinery applications this is the best choice. Having said that, think of PVA adhesives as a ‘family’ of products, not a single bottle of glue. PVA woodworking glue started out as a standard formula. Water-resistant varieties (Type II) and outdoor water resistant (Type III) exist. Fast-setting formulas allow you to glue up moulding and small parts that are difficult to clamp. If your assembly time will exceed 8–10 minutes, extend time glues allow an extra 5 minutes to get your project in clamps. If you are using dark woods (such as walnut), the dark tinted version may help hide the glue line better. A clear version is also available for situations where you do not want the yellow tint. An example of this application is if you do a lot of veneering, if you work with melamine, particle board or MDF, a special formulation of PVA glue exists for these more difficult to bond wood products.
In my shop I do a lot of general-purpose woodworking and furniture making. I do not use a lot of sheet goods (plywood, MDF, etc.), instead mainly making my projects from domestic hardwoods. Most of my work is intended to end up indoors. I also do a lot of woodturning and cutting boards, with those pieces intended to be used and hand washed. I keep a bottle of Type II and a fast-setting glue on hand. If I am doing a large complex project (like a desk I recently built) I switch to an extended time Type II. I find that Type II works great on inside work, gives better water resistance and seems to apply just like traditional PVA. I use a wet rag to wipe up excess glue on my projects. A few hours later I take a utility knife tip to any little squeeze-out I find in corners.
PVA has a two-year shelf life from when it is made. Learn how to read the date code on the bottle. I try to buy glue in quantities that I will use up every 3–6 months. Keep PVA glue from freezing. Wipe dust off your work before gluing as glue will stick to wood dust, rather than your boards, and weaken the joint. PVA glue is not intended to fill gaps or fix bad joinery. If you can get a razor blade into the joint you are probably at the edge of what is an acceptable gap.
Using proper clamping pressure is critical to achieving a strong joint with PVA glue. The trigger-style, one-handed clamps, and spring clamps do not provide optimal clamping pressure for glue-ups. Bar clamps, pipe clamps, F-style clamps, parallel clamps, C-clamps and wood clamps are all better choices. Spacing of clamps matters, so try to space clamps every 200–255mm and near each end. If you have to bridge longer distances a caul will spread the clamping force more evenly. A slightly convex board clamped on each end will exert force into the centre of the span. I leave clamps on for 24 hours. The glue manufacturers usually recommend less, but glue takes 24 hours to cure and by leaving them in clamps I don’t mess with the project before I should.
White craft glues
If your woodworking involves small parts, cloth, paper, leather, mosaic tiles, glass, china or other unusual materials these adhesives are great. I make a lot of toys and holiday decorations and use these adhesives throughout those projects. Unlike CA glue, white glues are more flexible and seem to survive drops and daily life. They also allow fixing things around your home and may increase your overall tool allowance.
When you have a small piece of trim or moulding that is impossible to clamp, these adhesives can be held in place with your fingers or a piece of masking tape. The high tack and quick initial set of these glues are just the thing. They dry clear, can be painted or stained and solve a lot of life’s little problems. A couple of drops lets you glue plugs into countersinks, adhere wood knobs onto drawers, and fixes lifted veneer ends and small lifted slivers of wood.
Adhesives for laminating
If you do bent lamination or want to add curved elements to projects there are adhesives that can help you achieve success. If you use regular PVA glues they can sometimes ‘creep’ or spring back. Leaving your lamination in clamps a full 24–36 hours to allow the adhesive to fully cure can help with this situation. Using a specialised form of PVA adhesive is another way to minimise this problem.
Gluing up multiple layers takes time. Getting glue on every layer, getting the ‘sandwich’ into the form and getting the clamps on may be hard to accomplish with the 8–10 minute open time for traditional PVA glue. Extended glues give you another 5 minutes of working time. If you need more than that, plastic resin glue is a good alternative. You can have up to 30 minutes to get everything clamped up. However, plastic resin glue is not to be trifled with! Read and follow all the safety precautions. Wear gloves, do not breathe in the glue dust, wear eye protection and mix carefully. This glue dries like sharp glass so be careful not to get cut on the cured resin. It will also dull joiner and planer knives, hand planes and chisels. Even carbide tip router bits take a beating with this adhesive. I use a belt sander for initial sanding and will replace the belt often after the project. One last note of caution: this adhesive needs to be used in a very specific minimum temperature range (around 21°C/70°F) for the entire glue-up and 24-hour cure period. So really, read and follow the instructions.
Polyurethane glues
When polyurethane glues first hit the market, I, like lots of others, bought a big bottle and had mixed results. I didn’t read the instructions, and thought it was just a better marketed wood glue (who could resist the strength of a gorilla?). Well, I made a mess of everything. There was this odd ‘foam’ oozing from the joints, it wouldn’t come off my fingers and the glue in the bottle wasn’t usable when I opened it up for another project.
Only years later did I learn to read and follow the instructions and understand how to use this adhesive. Polyurethane glue looks like molasses as you pour it from the bottle. It needs one (or both) surfaces to be wet for it to cure properly. Polyurethane glue is not gap filling so it needs tight joinery to work properly. Use good clamping pressure as you would for a PVA joint. You will note that the bottle is upside down in its holder. You do not want air in the nozzle during storage or the entire bottle will harden. Even with proper storage, 6 months is the lifespan for an open bottle of this adhesive, so I buy small bottles, glue in batches and use it up. You must wear gloves, if you get this on your skin it will not come off. Most importantly, keep this product away from children and pets. If swallowed it will expand within the body and cause serious injury or death. In fact, the manufacturer maintains a dedicated 800 number with medical support on the phone to help with emergencies caused by this adhesive. That should help you appreciate just how much you need to respect this product and follow the safety warnings.
Despite its limitations and risks, in the right application polyurethane glue can give a very strong bond. It sticks to a wide range of surfaces, when cured is waterproof, and creates a somewhat flexible bond. So, on applications like doors (that get repeatedly slammed), pen tubes and bottle stoppers (that get frequently dropped) and other applications where its traits are helpful, consider this product. Most furniture makers do not use it for joints that will show (such as table tops or panels) as the joint seems to be more visible than PVA when dried.
Furniture restoration glues
I do not do much furniture restoration, but every once in a while some piece of old furniture arrives in my shop. Now, I would not touch anything of any provenance, but most of what I see is just old stuff from someone’s grandma’s home. If you have furniture over 75 years old it was probably assembled with hide glue. Hide glue has been around for centuries and, if you are working on old furniture, have the respect to make any repairs with the same type of glue originally used whenever you can. Hide glue has a unique trait that a cured joint can be reversed (the glue can be softened until it lets go without force) by the application of some hot water or steam. This means old dovetailed drawers and chairs can be taken apart, the old glue can be scraped
off, damaged parts replaced and the whole piece glued back together. Since this is made from animal bones, hides and collagen are the base components. So, when you open the bottle be ready for it to stink up your shop! Other than that, and a shorter shelf life, it has little downside. On the opposite end of the spectrum many furniture restorers rely on two-part solid epoxy sticks to replicate missing details on antique furniture. Wear gloves when using this product to protect yourself. It seems harmless like playdough, but it contains dangerous compounds that can harm you. The inner part is one colour and the outer part another. You cut off a piece with a knife, and knead the two parts together. You have plenty of time to push it into place and then sculpt it like clay to replace missing details (like bits the dog chewed off). After it dries it can be carved, sanded and stained (use a gel stain) like wood.
CA glue
Cyanoacrylate (CA) glue was another product that the marketing geniuses rebranded as ‘super’ glue. This caused the product to be misused by us in our shops. Now, as I get older, hopefully I am getting wiser (a debate among my family) so I am learning what CA works well for, and when another adhesive is better. Clearly it has a place, but it also has limitations.
CA comes in various viscosity forms from thick to thin. The medium and thin variants are staples in my shop. Many brands of CA have a proprietary accelerator that must be used with their product. Others can use any accelerator. Typical application for bonding two pieces together is to put CA on one piece and spray the other with accelerator. They will bond quickly when put together with finger pressure. Alternatively, put CA on one piece and put the pieces together, then mist the assembled joint with a little accelerator.
CA glue bonds dissimilar materials, but cannot be used on cloth (it can create an exothermic reaction and burn your shop down). I like to make furniture and woodturned pieces that retain knots and natural defects. Thin CA glue can soak into the area around knots, punky wood, spalted wood that isn’t as sound as you would like and other areas and help harden the fibres. When I am trying to stabilise these situations I use a small tip and put some CA into the defect. If you can have the wood on a flat surface (that is protected in case the CA leaks all the way through) the CA glue will not run into areas you do not want it to flow into and stain surrounding areas. CA does impact finish penetration so take this into account. When using CA in this way I do not use an accelerator. I put on a thin coat, and walk away. Twenty minutes later (or when I remember) I come back and put on another coat. By not using accelerator I let the CA soak in as deep as it can. I may repeat this process several times, sometimes block sanding the area between applications to see if the defect is responding well to the CA treatment.
Use CA in a well-ventilated area. Note that CA bonds skin all too well so have acetone around in case you bond your fingers together. Accelerator should be used sparingly. Try not to inhale it and be aware of your body if you seem to be sensitive or react to its use.
Epoxy
Epoxies are two-part products that when mixed together in a specific ratio (usually either 1:1 or 2:1) start a chemical process that will harden into an incredibly strong bond. Epoxy creates a waterproof bond (it is used for boat building), can fill gaps that will be structurally as strong as the surrounding wood and will bond almost any surface to any other. River tables, inlays and all types of popular current projects use epoxy to achieve their visual result. It can be tinted, materials can be embedded into it and it can be used as a surface finish.
Epoxies vary as to their clarity and open time. Look for clear epoxies if clarity matters. Five-minute epoxies are fine for small repairs but do not leave much working time for complex joinery or involved repairs. My favourite epoxy is 30-minute clear epoxy that is mixed in a 1:1 ratio. It costs a little more, but it is versatile for the types of woodworking I do and simple to mix correctly. The longer open time allows more bubbles to clear out of the work and there is less stress when mixing and using this product.
There are a series of safety considerations when using epoxy. First, read the instructions and take the time to understand them before proceeding. Wear gloves and other PPE. Use clean, disposable mixing cups (I use those little graduated medicine cups), lolly sticks and put some protection down on your workbench.
Mix thoroughly, but slowly. You do not want to introduce any more air bubbles than you have to into the container. When I am using 30-minute epoxy I will let it rest a few minutes, or pour into a second cup and remix to make sure I have both parts completely incorporated. (The first part you poured into the cup seems to stick to the cup sides and you get an uneven mix.) If I have any mix ins (tint, or some other decorative element) I add it now. The longer your open time the more time there is for bubbles to come to the surface. If you are careful, you can wave a butane torch over the surface and it will cause more of the bubbles to pop and disappear. Have a fire extinguisher nearby if you try this tip.
Pressure-sensitive tapes
These products should not be confused with the inexpensive two-sided ‘carpet tapes’ or foam-backed double-sided tape. Pressure-sensitive tape is stronger, more expensive and designed for woodworking. The thicker cloth-backed tape is for temporarily mounting work. You can use it
to temporarily hold small parts for sanding or finishing. It has several applications for woodturners, such as mounting thin pieces of wood to faceplates. If you make jewellery it may allow you to hold work by taping it to another board for carving or embellishing. In short, it is handy. The thin version of the tape is intended to replace glue in some woodworking situations. I have used it to put laminate end caps on cabinets, mount delicate trim that couldn’t be tacked in place with a small pin nailer and other projects. I also use it for mounting drawer fronts to drawer boxes. A few small pieces of tape allow you to get the drawer front in the right place and hold it securely until you screw it from the back. It is a great problem solver and I have never had it come loose.
Please note, you must apply adequate pressure for this product to work. I use a J roller whenever possible and apply as much force as possible. Alternatively, apply clamping pressure to cause the adhesive to fully bond.
Spray adhesives
This is another product where quality matters. If you scrollsaw, this is a great product for mounting patterns to the wood. If you put felt liners in drawers or jewellery boxes this is a way to affix the felt. If you do any upholstery this spray adhesive helps hold foam and batting in place while you are stapling the piece together. Need to put cork into a coaster? This is the adhesive for the job. Read the instructions as they are specific about the distance you should hold the can from the work, and how long to leave the pieces apart to tack before assembly and most importantly safety precautions.
This stuff is flammable, the vapours are powerful and you need to use PPE. The green can shown in photo 17 is a really powerful adhesive. It can be used in place of traditional contact adhesive and will permanently bond laminates to surfaces. It will adhere edge banding on plywood and MDF, bond panels together, affix veneer to substrates and other tough tasks. It is really an industrial product, so treat it with respect. Read the instructions and heed the precautions (which are even more stringent than the above adhesive).
Contact adhesive
If you work with laminate countertops, veneer or other materials where you bond one sheet of something to another, contact cement is a great helper. In addition to the green spray adhesive in the last section, there are contact adhesives for this application.
Read the instructions as they are specific to this type of product and those instructions also vary between brands. Watch the environmental range required for application as it may be hard to maintain when you have all the windows open. There are two basic types of contact adhesive: the old solvent type that needs very good ventilation, is flammable, can cause all types of health problems, and the water-based type that is meant to address those shortfalls. Here is the catch – the old solvent type bonds better and seems to out perform the water-based product. A third type is a form of the pressure-sensitive tape mentioned above and marketed to cabinetmakers for field installation of laminates that cannot be pre-applied in the shop. It is expensive, but works great. I use it whenever I can.
With the exception of the tape and spray type, traditional contact adhesive is sprayed, brushed or rolled onto each surface, so you need enough space to support both during this step. Then when they have partially dried (read the instructions as some require two coats on each surface prior to this next step) the pieces are positioned near each other, but not touching. Some woodworkers use dowels, others slats of wood (and some others old mini blind blades) to keep the two parts from touching, but get everything in perfect position. You only get one shot at this so take the time to get everything in alignment. Once the two surfaces with contact cement touch they are bonded forever. Then remove one spacer and push down the first inch or two, then another, then another, using a J roller to push down firmly and work out any air bubbles. You cannot go back and fix a mistake, so get this right. Once all the spacers are removed most manufacturers require you to roll every inch of the laminate with a J roller, using strong pressure, to make sure everything is bonded together. It is a specialised product that makes a permanent bond that will last for years when properly applied, so put the time into learning how to use the product before you start.
One professional tip, you do not want any debris to get on the side you are applying adhesive to. This includes debris as small as a bristle out of a paintbrush. Have some tweezers handy and make sure you keep the surface clean. Any debris will telegraph through the surface and make an unsightly bubble or bump that never bonds.
Construction adhesives
This may seem like a strange category, but these adhesives can be very helpful for woodworkers. Originally designed to help builders bond sheathing and plywood to joists and studs, it has evolved into a family of products for use in the home shop. These adhesives are strong, flexible, grab instantly and are gap filling. Their downside is that they can leave ugly joints (the adhesive is too thick to disappear between two pieces
of wood so you need to disguise the joint) and do not wash off if spilled on wood or if you have squeeze-out. I use them for jigs, some situations where I will not be able to create a perfect mating surface between the two boards (such as when a bent lamination touches another furniture element), for outdoor furniture (particularly log or twig furniture) or for gluing dissimilar surfaces together. You will not use them all the time, but they are handy, particularity in a small squeeze tube.
PHOTOGRAPHS BY MARK PALMA