Wood glue is one of the most essential tools for any woodworker. Selecting the right adhesive for your project can make the difference between a piece that lasts for years and one that falls apart. With the variety of options available, it’s important to understand the strengths and limitations of the main types of wood glue.
The most common choice for indoor woodworking is polyvinyl acetate, better known as PVA glue. Easy to use and affordable, PVA glue provides a strong bond for most indoor applications. However, it is not waterproof and thus not suitable for outdoor projects. For exterior woodworking or pieces exposed to moisture, polyurethane glue is a better option. Polyurethane glues resist water, though they can be messier to work with.
Beyond PVA and polyurethane, other specialty glues have their uses. Epoxy creates an ultra-strong bond and can fill gaps in misaligned joints. Cyanoacrylate glue, also called super glue, affixes pieces in an instant but does not provide lasting shear strength. The ancient hide glue requires heating but can be reversed with sufficient heat and moisture. With knowledge of their different qualities, woodworkers can select the ideal adhesive for durable and long-lasting projects.
The variety of glues available means every woodworking project can get the bonding solution it needs. In this article, we will explore the leading types of wood glue so you can confidently choose the right adhesive for superior results.
Polyvinyl Acetate (PVA) Glue
Also called yellow glue or white glue, polyvinyl acetate (PVA) is the most popular and versatile glue for DIY woodworking. Major brands like Elmer’s, Gorilla Glue, and Titebond offer PVA-based wood glues.
PVA glues are inexpensive, non-toxic, and readily available at any hardware store or home center. The thick, syrupy consistency makes application easy with a brush, roller, or glue spreader. PVA dries clear with a glossy finish that blends into the wood seamlessly. It cleans up easily with water if excess squeeze-out needs to be removed.
Once fully cured after 24 hours of clamping, PVA forms an incredibly strong bond suitable for indoor and outdoor applications. It creates a joint stronger than the wood itself. The shear strength exceeds that of hide glue, cyanoacrylate, and even polyurethane in most cases.
While water-resistant when dry, PVA glue has limitations in extreme damp environments. For water immersion projects like boats, polyurethane or epoxy adhesives are a better choice. The open time of 10-20 minutes also requires keeping joints clamped for longer versus cyanoacrylate glues. And PVA glue’s viscosity prevents use in very close-fitting joints.
Overall, PVA wood glue is the ideal all-purpose adhesive for the vast majority of carpentry, joinery, and hobbyist woodworking. Its versatility, strength, low cost, and convenience make it a staple product for every workshop.
Cyanoacrylate (CA) Glue
Also referred to as super glue or instant glue, cyanoacrylate (CA) glue provides an ultra-fast bond by rapidly polymerizing when pressed between surfaces. On porous materials like wood, it will start to grab and harden within 5-60 seconds of application.
The quick bonding allows you to tack small wooden parts in place almost instantly. Hobbyists value CA glue for assembling wood models and attaching dowels, pins, and rods when speed is paramount. It can temporarily hold pieces together for easier clamping of slower-curing wood glues.
Thin CA glues penetrate into gaps through capillary action for an ultra-strong bond. They work exceptionally well for bonding leather, rubber, plastic, metal, and more to each other and wood. Medium and thick CA viscosities bridge larger gaps. Activator sprays containing sodium hydroxide can decrease cure times to just a few seconds.
However, limitations of cyanoacrylate glue include brittleness and relatively low bond strength for load-bearing wooden joints. It does not provide the shear or tensile strength of an epoxy, PVA, or polyurethane bond. The rigid cyanoacrylate will fail before the wood substrate does. For critical structural joints or large projects, CA is not the ideal adhesive.
CA glue also lacks gap-filling abilities, though using it as a sealant prior to applying a thicker glue can improve end results. Super glues have little moisture resistance as well. But for sheer speed in temporarily tacking parts, its rapid cure time can’t be beat.
Epoxy Glue
Epoxy adhesives are formed by mixing two components – a resin and a hardener – in the proper ratio which triggers a chemical reaction. This reaction causes the liquid or putty to harden into an extremely rigid plastic polymer.
Unlike one-part glues, epoxies require thoroughly stirring the resin and hardener together for at least 3-5 minutes to achieve an even cure. Most have a working time of 10-45 minutes before the mixture starts to harden. Clamping pressure should be applied immediately after mixing.
Epoxy glue forms incredibly strong, waterproof bonds. When used as an adhesive between boards, epoxy withstands over 2,000 psi of tension, versus just 600 psi for PVA glues. The rigid epoxy also transfers stress extremely evenly across the joint.
Thanks to these properties, epoxies excel at filling gaps, cracks, and misaligned joints in wood. Mixed with sawdust, epoxy can invisibly patch damaged furniture. Plastic-safe epoxies like JB Weld bond dissimilar materials like metal and ceramic. Once fully cured, epoxy sands and takes paint or stain like wood.
However, epoxies have downsides including high cost, toxicity, and very long cure times up to 24 hours for full strength. The thick viscosity and slow setting time makes epoxy impractical for general assembly tasks. But when used properly, nothing surpasses epoxy for durability and strength.
Hide Glue
Hide glue is a traditional adhesive made from animal collagen through hydrolysis. It was originally produced by boiling animal hides, bones, tendons, and other tissues. Hide glues were the primary woodworking adhesive for centuries before synthetic options became available.
When liquefied by heating to 140°F or more, hide glue has a low viscosity comparable to water. It penetrates wood pores for good mechanical adhesion. Traditional hot hide glue provides an open time of just a few minutes before starting to thicken and grab. Hide glue joints reach maximum strength once fully cured over 24 hours.
Modern hide glues with extended open times and room temperature use are also available. But in general, hide glues are less convenient to use than modern adhesives. They have low moisture resistance as well.
However, hide glue excels in antique repair. A hot iron or chemical stripper softens hide glue, allowing non-destructive disassembly of furniture for restoration. Its moderate tack also makes hide glue ideal for delicate materials like veneer or inlay.
For general woodworking, hide glues have been surpassed in most applications by PVA and other adhesives. But they still lend themselves well to traditional woodworking requiring reversibility or moisture control.
Polyurethane Glue
Polyurethane glue cures through a chemical reaction with moisture present in the air and wood. It was originally developed in Germany during the 1930s but didn’t gain widespread use until decades later.
Polyurethane glues have excellent water resistance, unlike PVA adhesives. This makes polyurethane the best choice for outdoor projects that will be exposed to rain and other wet conditions. It can even glue end grain-to-end grain joints which are impossible for PVA glues.
The viscosity is similar to conventional wood glue. Polyurethane has an extended open time around 30 minutes versus just 10 minutes for common PVA wood glue. This allows more time for positioning intricate joints.
On the downside, polyurethane glue tends to foam and expand slightly during cure. This expansion can swell into gaps but also purse pieces outward. Careful clamping is required to avoid deformation of the wood surface. Invisible joints demand very precise mating.
Polyurethane glue also costs substantially more than PVA – often 5 to 10 times as much. Combined with the technical difficulties in use, this restricts polyurethane to specialty applications where PVA falls short.
But for critical outdoor projects and unique situations like bonding exotic oily woods, polyurethane is the right choice. Just take care to correctly account for the adhesive’s expansion and limitations.
In summary, the variety of wood glues available gives woodworkers suitable options for any job. PVA tackles most indoor projects while polyurethane excels outdoors. CA offers speed and epoxy provides unrivaled strength. There is a best glue for every task with the proper knowledge. Understand the capabilities of each adhesive and select the ideal one for flawless wood joints that endure.
Comparison of the main types of wood glue
| Glue Type | Description | Strength | Speed | Viscosity | Gap Filling | Moisture Resistance | Cost |
|---|---|---|---|---|---|---|---|
| PVA | Polyvinyl acetate, water-based. Common “carpenter’s glue”. | Strong | Slow drying | Medium viscosity | Low | Medium | Low |
| Polyurethane | Two-part glue that cures with moisture. | Strong | Slow curing | Medium viscosity | Low | Excellent | High |
| Cyanoacrylate | Fast-curing “super glue”. | Weak | Extremely fast cure | Low viscosity | Low | Low | Moderate |
| Epoxy | Two-part adhesive that chemically cures. | Extremely strong | Slow curing | High viscosity | Excellent | Excellent | Very high |
| Hide | Made from collagen in animal hides/bones. | Medium | Slow assembly | Low viscosity when hot | Low | Low | Moderate |
- PVA wood glue is the most widely used adhesive thanks to its versatility, strength, ease of use, low cost, and water cleanup. It creates a durable bond stronger than the wood itself, suitable for indoor and outdoor projects. Limitations include longer clamping time versus CA glue and unsuitability for close-fitting joints.
- Polyurethane glue excels at bonding exotic oily woods thanks to its moisture-cure mechanism. The cured glue resists water far better than PVA. However, polyurethane is more difficult to work with, expands as it dries, and costs substantially more than PVA.
- Cyanoacrylate glue offers unmatched speed in temporarily bonding wooden parts. But it has low overall bond strength. CA glue works well for quickly securing pieces for subsequent gluing. It has little moisture resistance.
- Epoxy glue is the strongest option but also the most expensive. It has excellent gap filling properties. But epoxy requires precise mixing and can take a full day to cure. This makes epoxy less practical for general woodworking tasks.
- Hide glue has historical significance but modern limitations like low moisture resistance and heating requirements restrict everyday use. It remains ideal for antique restoration work.
Types of Wood Glue: Frequently Asked Questions
What is the best all-purpose wood glue?
Polyvinyl acetate (PVA) glue is the best option for most general woodworking purposes. It creates a strong bond, is easy to use, dries fast enough, and has a great price. PVA glues like Titebond are a woodworker’s staple.
Can you use wood glue outside?
Regular PVA wood glue is not waterproof enough for prolonged outdoor exposure. For outdoor projects, a weatherproof glue like Titebond III or polyurethane glue is a better choice.
How strong is wood glue?
Most PVA wood glues create a bond stronger than the wood itself, in excess of 3000 psi. The joint typically fails by breaking the wood fibers, not the glue. Polyurethane and epoxy can be even stronger.
What is the fastest drying wood glue?
Cyanoacrylate (CA) super glues offer the fastest cure, bonding pieces in just seconds. But CA glue has lower overall bond strength. It’s best for quickly tacking parts.
Can you re-glue wood?
Wood can be re-glued effectively if the old glue is removed completely. Scrape off old PVA glue and sand the joint to bare wood. Make sure surfaces are clean and dry before reapplying fresh glue.
What glue works best on metal to wood?
Epoxy provides the strongest bond between dissimilar materials like metal and wood. CA super glue also works well. Ensure the surfaces are sanded and cleaned first.
Is wood glue toxic?
Most common wood glues like PVA, polyurethane, CA, and epoxy are non-toxic when fully cured. Some can irritate skin prior to curing. Always follow safety precautions.
Can wood glue go bad or expire?
Opened PVA glue lasts 1-2 years when stored properly, while cyanoacrylate lasts around 1 year. Epoxy has a shorter shelf life around 6 months. Follow manufacturer expiration dates for best results.
Conclusion
When it comes to assembling beautiful and sturdy wood projects, the right adhesive makes all the difference. Wood glues come in various formulations optimized for different applications and working styles. Versatile PVA glues tackle indoor jobs with ease thanks to their strong bond, fast drying, and water clean-up. Polyurethane excels at outdoor projects, oily exotic woods, and end-grain joints. Epoxy’s unparalleled strength fills gaps that other glues can’t while CA glue bonds in seconds for those in a hurry. Hide glue maintains tradition for reversibility. Whatever your purpose, there is a wood glue that will give you outstanding results. Do your joints justice by matching them to their ideal adhesive partner.
