Glues and Adhesives
Glues and Adhesives Explained
The majority of glues and adhesives are one of several material types: Epoxy; Urea-Formaldehyde; Polyurethane; Aliphatic Resin Wood Glue (Yellow Wood Glue); Polyvinyl Acetate (PVA) Wood Glue, Cyanoacrylate (Super Glue), Methacrylate (Structural Adhesives) and Silicone Rubber (RTV).
In addition, there are numerous application-specific glues and adhesives (contact cement, construction adhesives, spray adhesives, carpet adhesives, etc.) that will not be part of this discussion. Choosing the correct type of adhesive or sealant is not difficult once the application, materials to be bonded and the sealant characteristics are understood.
Epoxy Adhesives
Products and Brands: WEST System Six10, G/flex; System Three T-88, Silvertip Gel Magic; Permatex PermaPoxy; Gorilla Epoxy; Pettit Flexpoxy; 3M Scotch-Weld Epoxy
- Where to use: Epoxy-based adhesives form high strength, water-resistant bonds on a wide variety of materials, including wood, metals, concrete, ceramics, fiberglass, carbon fiber, plastics and most rigid surfaces.
- Do not use for: UV exposed applications. Does not bond to StarBoard.
- Cure time: Cure takes 2-6 hours, depending upon ambient temperature, and various speed hardeners are typically available.
- Cautions: Avoid prolonged or repeated skin contact. Use only in well ventilated areas.
Two Part Epoxies: Epoxy is one of the most versatile of adhesives since it will readily accept a wide variety of additives including fillers, wood flour, graphite powder, aluminum powder, silica thickeners and a range of colored pigments. Hardeners are available in a variety of speeds (slow, medium, fast) and viscosity. Epoxy is the ideal choice for secondary bonding and repair of fiberglass boats. Epoxy is considered to be a major part in the class of high-performance materials called "structural adhesives" or "engineering adhesives". Epoxy adhesives are used in the construction of aircraft, automobiles, bicycles, boats, golf clubs, skis, snowboards, and other applications where high strength bonds are required. Epoxy readily bonds with a number of fiber reinforcements including fiberglass, carbon and Kevlar.
Pros: Two part epoxies are waterproof when cured (ideal for boatbuilding), versatile, long working time, high tensile strength, heat resistant (up to 175-200 degrees F), good for a number of substrates (not just wood), good for oily wood, long shelf life
Cons: Expensive, unforgiving to use and when mixing, difficult to clean up, long cure time, requires more safety equipment than some other wood glues.
Examples: WEST System, MAS Epoxies, System Three Resins (see the Epoxy Resin section)
5 Minute Epoxy: Similar to the standard two-part epoxies, but optimized for quick cure time. Some brands are waterproof, others are not. All 5 minute epoxies are a 1:1 mix ratio, by volume. Some brands state that fillers may be added.
Pros: Quick curing, short clamping time, easy to mix, good for use on a variety of substrates.
Cons: Quick curing, less work time, not as strong, only System Three and MAS are waterproof, not appropriate for larger applications.
Examples: WEST System G-5; System Three Quick Cure; MAS Rapid Cure; Permatex 5 Minute Epoxy; Gorilla Epoxy
Flexible Epoxy: Flexible epoxy is a toughened, versatile, liquid adhesive used for permanent, waterproof bonding of fiberglass, ceramics, metals, plastics, damp and difficult-to-bond woods. More flexible than standard epoxies and polyester, but much stiffer than adhesive sealants making it the ideal choice for bonding dissimilar materials. It can be modified with fillers and additives, and used to wet-out fiberglass tapes and fabrics. Flexible epoxy resin can be used above and below the waterline in large and small repair jobs, on fiberglass, (including blister repair), wood, steel and aluminum hulls and topside sections with good results.
Examples: WEST System G/flex; Pettit Flexpoxy; Marine-Tex FlexSet
Urea-Formaldehyde Adhesives
Products and Brands: Weldwood Plastic Resin Glue
- Where to use: Bonds a wide variety of woods. Forms a high strength, water-resistant bond.
- Do not use for: Materials other than wood.
- Cure time: 1-4 hours depending upon ambient temperature, mix with water.
- Cautions: Avoid prolonged or repeated skin contact. Use only in well ventilated areas. Do not use containers or tools of copper or copper bearing alloys to mix adhesive.
Urea-Formaldehyde glue is a powdered, pre-catalyzed water-activated adhesive designed to provide strong, durable bonds for wood and wood products. This wood adhesive is an excellent glue for the craftsman, artisan or hobbyist. Urea-Formaldehyde glues are resistant to fungi, bacteria, oil, gasoline, or solvents. It creates a high strength, rigid seal upon curing and is ideal for adhering curved or bent structures. It is a water resistant system when cured, but water-soluble when uncured making for easy cleanup.
Pros: easy to use, long cure time, ideal for veneers, cures at room temperature, less expensive than epoxy
Cons: contains formaldehyde - thus good ventilation, respirators, and gloves are highly suggested, long clamp time, shorter shelf life than epoxy
Examples: Weldwood Plastic Resin Glue (one-part, mixed with water)
Polyurethane Adhesives and Sealants
Products and Brands: Gorilla Glue, 3M Scotch-Seal Polyurethane Adhesive Sealants, 3M Scotch-Weld Urethane Adhesives, 3M 5200, 5200 Fast Cure, 4200 Fast Cure; Sikaflex 201US, 252, Sika-292, Sika-296, Sika-295UV, Sika-521UV, Sika-291, Sika-221
- Where to use: Bonds a variety of materials - metal, stone, wood, ceramics, foam, glass and more.
- Do not use for: Paper products or rubber materials.
- Cure time: 1-2 hours and longer depending upon formulation, one component and two component versions, moisture curing adhesives.
- Cautions: Avoid skin and eye contact. The use of protective gloves is highly recommended.
Polyurethanes are offered in both one-part and two-part systems. They are simple, strong and easy to use. Polyurethane adhesives are ideal for the laminating of porous materials like wood. Polyurethanes are water proof, but moistening the surface before applying accelerates the curing process. Polyurethane adhesives are available in flexible and non-flexible formulations.
Polyurethane adhesive sealant products form an extremely strong bond while retaining flexibility and strength above or below the waterline. Watertight bonding / sealing of fiberglass, gelcoat and wood. Alcohol should not be used when preparing surfaces for bonding as it will stop the curing process, causing the adhesive to fail. Polyurethane sealant products are not recommended for use as a teak deck seam sealer. Extended exposure to chemicals (teak cleaners, oxalic acid, gasoline, strong solvents and other harsh chemicals) may cause permanent softening of the sealant.
Aliphatic Resin Wood Glue (aka Yellow Wood Glue)
Products and Brands: Titebond Original Wood Glue
- Where to use: A wood glue designed to work on porous materials only.
- Do not use for: Non-porous materials and surfaces. Not for structural or load bearing applications. This glue is not intended for exterior use or where moisture is likely.
- Cure time: Fast setting.
- Cautions: Avoid prolonged or repeated skin contact. Use only in well ventilated areas.
Titebond Original Wood Glue is ideal for wood, hardboard, particleboard, leather, cloth and most other porous materials. Titebond Original is easy to use, non-toxic and cleans up with water. Also known as yellow glue or carpenter's glue.
Polyvinyl Acetate Adhesives (PVA Wood Glues)
Products and Brands: Titebond III Ultimate Wood Glue, Titebond II Premium Wood Glue; Gorilla Wood Glue; DAP Weldwood Carpenter's Glue
- Where to use: PVAs are suitable for most varieties of wood. Ideal for both interior and exterior applications.
- Do not use for: Non-wood materials and surfaces. Not for continuous submersion or for use below the waterline. Not for structural or load bearing applications.
- Cure time: Clamping time is 20 - 30 minutes and full cure within 24 hours.
- Cautions: Avoid prolonged or repeated skin contact. Use only in well ventilated areas.
PVA Workshop Glues are non-toxic, solvent free and clean up with water, making them safer to use than traditional waterproof wood glues. PVA glues provide a strong initial tack, sand easily without softening and are FDA approved for indirect food contact (cutting boards). May be used for both interior and exterior applications.
Cyanoacrylate Adhesives (Super Glue)
Products and Brands: Permatex Super Glue, Permatex Super Glue Gel; Bondo Super Glue, Loctite Quicktite Super Glue, Gorilla Super Glue
- Where to use: Glues nonporous materials including metal, alloys, plastics, rubber, vinyl, paper, wood, textiles, ceramics and cork gaskets.
- Do not use for: Porous materials and surfaces.
- Cure time: Cures at room temperature on exposure to moisture. Fixture time is 15 - 30 seconds and full cure within 24 hours.
- Cautions: Avoid skin and eye contact. Yes, you can glue your fingers together - don't do it!
Cyanoacrylate or "super-glues" are one-component, solventless, instant adhesives based on cyanoacrylate resin. Super Glues cure instantly, form a waterproof bond and do not require clamping. Two downsides of Super Glues are that they are relatively costly and that the resulting bond is extremely brittle. The thinner the Super Glue is applied, the stronger the bond. The better the fit between the surfaces, the better the bond. Set up times will vary depending upon the type of surface.
Methacrylate Structural Adhesives
Products and Brands: 3M Scotch-Weld DP8005, DP8010; Plexus MA 300, 310, 832, 320, 530, 550, 4020, 425; SikaFast 3121, 3141; Weld Mount AT-4020, AT-2010, AT-1030
- Where to use: Methacrylate adhesives are designed for structural bonding of nearly all thermoplastics, metals, and composite materials.
- Do not use for: Porous materials and surfaces.
- Cure time: 8-24 hours.
- Cautions: Avoid prolonged or repeated breathing of vapor. Avoid contact with skin and eyes.
Methacrylate adhesives have been developed to perform under a wide range of conditions. This has been achieved by improvements in curing, bonding, adhesion and toughening additives. Methacrylates are structural adhesives which defines a class of high performance bonding materials which can withstand high loads under a variety of different stresses for great periods of time. Methacrylate adhesives are often be used in place of mechanical fasteners thereby simplifying assembly and distributing stresses over a greater surface areas.
Silicone Adhesive Sealants (RTV)
Products and Brands: Permatex Clear or Black Silicone Adhesive Sealants; 3M Ultrapro High Temp Silicone Gasket, 3M Marine Grade Silicone Sealant; Boatlife Marine Silicone Rubber
- Where to use: Head plumbing applications, interior & exterior wood, trim sealing and as a gasket adhesive.
- Do not use for: Silicone Sealant is not recommended for the installation of glass, polycarbonate (Lexan) or acrylic (Plexiglas) windows that are not also mechanically fastened. Do not use silicone on any surface to be painted.
- Curetime: a day or less.
- Waterline: used above the waterline only.
- Chemical Resistance: unaffected by most chemicals.
- Cautions: Avoid prolonged or repeated skin contact.
Silicone sealants are mildew resistant, non-sagging, moisture curing products, suitable for above the waterline applications only. Silicone products remain flexible with excellent resistance to the marine environment. Silicone adheres to bare and painted metal, glass, fiberglass, non-oily woods, many plastics and abraded rubber. Silicone sealants typically set in a few minutes while reaching a full cure in a day. Silicone adhesives are among the most durable and flexible products suitable for many sealing and bonding applications.
