Wood Glue
(4 Products)Wood glue is a specially formulated adhesive designed to bond timber and wood-based materials. It works by soaking into the wood's porous surface, then curing - either as water evaporates or through a chemical reaction - to create a strong, lasting bond. It's used in everything from basic crafts to heavy-duty construction projects.
What Is Wood Glue?
Wood glue is a specialised adhesive that bonds wooden pieces into a strong, unified structure. Unlike surface-only glues, it works by penetrating the wood fibres and forming a solid matrix as the water evaporates or the glue cures chemically.
When applied correctly with appropriate pressure, this cured glue line creates a bond so strong that the wood itself is more likely to break before the adhesive does. While unseen, wood glue is a foundational element responsible for the enduring strength of countless wooden structures and objects.
How It Works
Unlike general purpose adhesives, wood glues are designed to work with the unique cellular structure of timber. Their effectiveness relies on several principles:
- Penetration: Most wood glues are liquid and designed to penetrate the porous surface and wood fibres. This creates a deeper, more integrated connection rather than just a surface-level stick.
- Mechanical Interlocking: As the glue cures, it hardens within these wood fibres, creating a strong mechanical lock between the joined pieces.
- Adhesion/Chemical Bonding: The adhesive molecules also form chemical bonds with the wood cellulose, further enhancing the strength of the joint.
- Film Formation: Water-based glues, such as PVA, work by evaporating water. This causes the glue's polymer particles to bond together and form a solid adhesive layer. Other glues, like polyurethane, cure through a chemical reaction with moisture.
For most wood glues (especially PVAs and polyurethanes), achieving maximum bond strength relies on wood-to-wood contact and adequate clamping pressure while the glue cures. This ensures the glue line is thin and the surfaces are held together.
Benefits
- Stronger Wood-to-Wood Bonds: Designed to penetrate wood fibres and create bonds that are often stronger than the wood itself.
- Compatibility with Wood Properties: Formulated to accommodate the natural movement (expansion and contraction) of wood to some extent.
- Tailored Performance: Different types offer specific properties like water resistance, gap-filling, or fast/slow setting times to suit the application.
- Finishability: Many wood glues, once dry, can be sanded, stained, or painted without significantly affecting the final appearance (though it's always best to remove excess wet glue).
- Optimised Viscosity: Generally formulated to have a viscosity that's suitable for application to wood without excessive running or absorption.
Polyurethane Wood Glues (PU Glues)
- These are incredibly strong, versatile adhesives that cure by reacting with moisture present in the wood and the atmosphere.
- Properties: 100% waterproof (typically achieving a D4 rating), excellent for bonding wood to a wide range of other materials (metal, plastic, stone, ceramic), and also effective on oily or resinous woods where PVAs might struggle. They expand slightly as they cure, which can help fill minor gaps (though tight-fitting joints and strong clamping are still essential to prevent the glue from pushing the joint apart).
- Best For: Exterior projects, boat building, bonding dissimilar materials, oily woods, applications requiring a fully waterproof bond.
Safety Considerations When Working with Wood Glue
- Always read and follow the manufacturer's safety data sheet (SDS) and instructions.
- Ventilate the work area, especially when working with solvent-based glues, polyurethanes, or epoxies.
- Wear gloves to protect your skin, particularly with PU glues (which can stain skin) and epoxies (which can cause sensitisation).
- Wear eye protection to guard against splashes.
- Keep out of reach of children.
Frequently Asked Wood Glue Questions
What Are Type 1 & 2 Wood Glues?
Wood glues come in two distinct varieties: Type 1 and Type 2.
The former is waterproof, while the latter offers water-resistant protection. Both can also sustain a moderate amount of heat without breaking down.
How Long Does Wood Glue Take To Dry?
Depending on the wood, climate conditions and glue used, drying time can range from 10 to 30 minutes. While this may seem fast, remember not to confuse drying with curing; while one is completed in a matter of minutes, it takes up to 24 hours for wood glue to cure.
When Should You Not Use Wood Glue?
Bonding Non-Porous Materials:
- Standard wood glues (especially water-based PVAs) work by penetrating porous wood fibres. They will form very weak, if any, bonds on non-porous surfaces like metal, glass, most plastics, or rubber. For these, you'll need specialised adhesives like epoxies, super glues (cyanoacrylates), or contact adhesives designed for those specific materials.
Permanent Outdoor Exposure Without the Right Type:
- Most standard interior PVA wood glues (D1 or D2 rated) are not water-resistant or waterproof. They will fail quickly if exposed to rain, prolonged dampness, or significant moisture.
- For outdoor projects, you must use a waterproof wood glue (e.g., a D4 rated PVA, polyurethane glue, or exterior-grade epoxy). Even then, the wood itself will also need appropriate finishing and protection.
Significant Gap-Filling Requirements:
- Most PVA wood glues have poor gap-filling capabilities. They require tight-fitting joints for a strong bond. If there are large gaps or an uneven fit-up between wood pieces, PVA will not effectively bridge them and the joint will be weak.
- For significant gaps, a two-part epoxy adhesive is often a better choice as it can fill voids while maintaining structural strength. Polyurethane glues can foam to fill some gaps but require very tight clamping to prevent being pushed out.
Structural Applications Beyond Its Strength Rating (Especially for standard PVAs):
- While woodworking PVAs create bonds stronger than the wood itself in many joinery applications, not all PVAs are rated for heavy structural loads or critical structural elements in building construction without specific engineering approval.
- For very high-stress structural timber connections, mechanical fasteners (screws, bolts, timber connectors) are often used in conjunction with, or instead of, glue, or specialised construction adhesives might be specified.
Oily, Waxy, or Contaminated Wood Surfaces:
- Wood glue needs a clean, raw wood surface to penetrate and bond effectively. It will not adhere well to wood that is oily, waxy, greasy, painted, varnished, or heavily contaminated without thorough surface preparation (sanding back to bare wood, cleaning with appropriate solvents).
- For some naturally oily tropical hardwoods, polyurethane glue or epoxy might be more suitable than PVA as they can bond better to such surfaces.
Can I Remove Excess Glue After It Dries?
We've all been there; applying too much glue is a common joinery mishap. Luckily, you can shave hardened glue and remove it using a scraper or sandpaper. However, it is essential to be gentle to avoid damaging the wood surface.
Can I Mix Different Types Of Wood Glue?
It is not recommended to mix different types of wood glue as they may have different curing times and chemical compositions, which can result in an ineffective bond. It is best to use one type of wood glue for a project.
