Modern technology has resulted in a vast range of sophisticated adhesives. Each is designed for bonding specific materials and several types are used in woodworking. You may need additional glues for metals, plastics or inlay materials. It is also a good idea to keep a selection of adhesives for emergency repairs and general maintenance work in the workshop and around the home.
Polyvinyl acetate (PVA)
The most commonly used woodworking glue is PVA, which is a cold-setting adhesive. A good all-round glue with water-resistant properties in some types, it remains slightly flexible, even when set, allowing some movement of timber. It is easy to clean up with a damp cloth or paper towel. However, its high moisture content can make larger areas of veneer difficult as the moisture is absorbed within the veneer, leading to curling. If using cellulose-based polish, you will find the solvents mix with the PVA and can cause unsightly swelling on the glue line, called ‘creep’. Aliphatic resin (yellow) glue is a sophisticated PVA which has a fast initial grab, with a shorter cramping time necessary.
One of the most permanent and reliable of glues is synthetic resin, otherwise known as urea formaldehyde. Many brands are two-part adhesives: the glue is brushed to one joining surface while the hardener or catalyst is applied to the other. For the small workshop, mixing resin glue in powder form with water is easy (the powder incorporates the hardener). A general guide for resin glue shelf life is about three months, in dry conditions.
Polyurethane glue creates an exceptionally strong bond in a wide range of materials besides wood, including metals, ceramics and most plastics. It cures when exposed to moisture in the air, so shelf life is shorter than most other glues. Squeezed-out glue foams as it dries and can be chipped away before sanding. Used extensively for boat building, polyurethane glue is relatively expensive compared to PVA.
Made from the bones and skins of animals, this glue has been used for centuries and is still preferred by antique restorers, musical-instrument makers and those making reproduction furniture. Traditionally, animal glue is used in granule (pearl) or sheet form, soaked in water and heated — usually in an electric glue pot. You can also buy it in liquid form.
Although animal glue requires some preparation, the real advantage is that it is reversible: you can ease joints apart with a pallet knife and hot water. This makes it popular with luthiers, where awkward repairs may be needed later during the life of the instrument. Disadvantages include instances where air conditioning reduces the humidity levels upon which this glue relies. Many genuine antiques have lost their marquetry veneer owing to the dry environment in which they are kept. If in doubt, leave a bowl of water under a radiator to maintain the humidity needed for this type of glue.
Contact adhesive is latex based and relies on both surfaces being coated and meeting when touch-dry about 15 minutes — to form an instant bond. Although unsuitable for most woodworking tasks, it is used widely by kitchen and shop fitters for gluing plastic laminates to worktops and cabinets. In the workshop it is ideal for building projects, such as router tables or jigs, that need a laminate surface for durability. If used for veneering, the tension within the glue can pull veneers open in time and edges are likely to lift slightly, especially where humidity levels are high. You need a more permanent adhesive in cases where wood meets wood.
A two-part adhesive, epoxy resin provides incredible strength when bonding a wide range of materials, including metals and some plastics. Here, you mix glue and hardener in very small quantities, as working time can be just a few minutes before it starts to set. Epoxy is also available in syringe format for dispensing equal amounts of glue and hardener. This option is expensive but invaluable for repair jobs or gluing decorative inlays.
Also known as `superglue’, cyanoacrylate glues create a bond in seconds with the right materials. Useful for small repairs, such as chipped or lifting wood fibres, you only need a few drops. Available in liquid or gel form, cure times of some superglues can be increased by using a spray accelerator. Although it is easy to glue fingers together accidentally, de-bonders will soften and release any joint. This option is very expensive.
An electric glue gun distributes hot-melt glue in a continuous bead, and is very useful for mock-ups and temporary holding purposes, such as turning small items on the lathe. You feed a glue stick into the back of the tool and dispense it by pulling the trigger. Operating temperatures make glue-gun tips very hot, so make sure safety is a priority.
- Unless you are likely to be using large quantities for a project, always buy glue in small packs. Most have a limited shelf life, so you could end up wasting glue that is past its best.