Epoxy adhesives – High-strength, durable two-component bonds

What is Epoxy?

Epoxy (short for epoxy resin) is a high-performance thermosetting polymer that cures through a chemical reaction between two components: a resin and a hardener. Once cured, it forms a rigid, cross-linked plastic structure with outstanding mechanical and chemical properties. Epoxy epoxy systems are used across a wide range of industries, from aerospace and automotive to marine, construction, and model-making.

Epoxy adhesives are structurally stable two-component adhesives designed for durable, high-strength bonds. They adhere excellently to fibre composites (CFRP/GRP), metal, wood, ceramics and many hard plastics. Depending on the formulation, they are gap-filling, thixotropic or transparent. With the right choice, careful surface preparation and controlled curing, you can achieve reproducible bonds – from repairs to load-bearing joints.

What sets R&G epoxy adhesives apart

• High structural strength: Excellent shear and compressive strength; depending on the type, toughened for improved impact resistance and peel strength.
• Wide substrate compatibility: Ideal for CFRP/GRP laminates, aluminium/steel, wood and ceramics; with limitations for low-energy plastics.
• Process reliability: Defined pot lives and processing windows, room-temperature or heat curing for predictable workflows.
• Gap-filling and dimensionally stable: Thixotropic pastes do not run, are suitable for vertical surfaces and uneven joints; low-viscosity systems for thin, film-forming bonds.

Variants and applications

• Thixotropic 2-component pastes: For gap-filling bonds, edge builds-up, overhead bonding and form-fit with inserts. Good stability, uniform joint closure.
• Fast-curing formulations: Short working times for repairs and assembly, ideal for smaller areas and fixings.
• Toughness-modified types: Increased fracture toughness and peel resistance under dynamic or impact loads.
• Cartridges with static mixers or containers: Clean dispensing, reliable mixing ratio, process-reliable application.

Selection criteria for two-component epoxy adhesives

• Viscosity and thixotropy: Paste-like for gap-filling and vertical surfaces; low-viscosity for thin, uniform adhesive films.
• Pot life and open time: Short for fast cycles; long for complex joints, large-area bonding or insert assembly.
• Temperature resistance and Tg: For thermally stressed applications, plan for post-cure (e.g. 40–60 °C) to increase heat resistance.
• Toughness vs. stiffness: Toughened systems for better impact and peel strength; stiff systems for maximum shear values.
• Substrate: Bonding with epoxy resin works best on metal, CFRP/GFRP, wood and ceramics – on PE, PP, PTFE or silicone, adhesion is insufficient without special pre-treatment.

What is Epoxy used For?

Epoxy is used wherever strong, durable, and chemically resistant bonds or coatings are required. Typical applications include structural bonding of fibre composite parts (CFRP/GFRP), metal assemblies, wood constructions, ceramic repairs, and prototype manufacturing. Epoxy epoxy products are equally at home in professional industrial settings and in precision hobbyist or model-making work.

Surface preparation

• Degreasing: Clean with acetone or isopropanol, wipe with a lint-free cloth; do not use re-greasing cleaners.
• Mechanical roughening: Coarsely sand metal (e.g. 80–120 grit) or fine-blast; sand CFRP/GRP to a matt finish, ideally prepare with sanding cloth; ensure wood is dust-free and dry.
• Clean, dry bonding surfaces: Avoid moisture and dust; bond immediately after preparation; for gelcoat, completely remove release agent residues.

Bonding joint and application

• Recommended joint thickness: 0.1–0.3 mm for film-forming bonds; up to approx. 1 mm gap-filling with thixotropic pastes.
• Inserting spacers: Mix in glass hollow spheres or microspheres (e.g. 0.2–0.3 mm) or use separate spacers to ensure a consistent joint thickness.
• Dosing and mixing: Mixing ratio exactly by weight/volume; stir slowly and thoroughly; use a double-pot mix for containers; use cartridge systems with a static mixer.
• Application and fixing: Apply evenly, join components, remove excess before gelation; fix by applying pressure/clamping until hand-firm.

Curing and post-treatment

• Room-temperature curing: Hand-firm depending on the system after 30–180 minutes; final strength after 24–48 hours.
• Post-cure: Annealing (e.g. 40–60 °C) increases Tg, strength and media resistance; particularly recommended for thermally stressed applications.
• Finish: Remove any excess material cleanly before curing; can be machined after curing (grinding, milling).

Typical applications

• CFRP/GFRP: Structural bonding of ribs, stringers and flanges, inserts, repairs and reinforcements.
• Metal: Bonding of brackets, frames, covers; hybrid metal-composite bonding.
• Wood and furniture construction: Fibre-reinforced wood bonding, edge builds-up, component reinforcements.
• Ceramics/stone: Fixing and repair of hard, brittle substrates.
• Model making/prototyping: Precise, load-bearing joints in small-batch production and prototype construction.

Advantages and limitations

Advantages:

• High shear strength
• Excellent adhesion
• Good chemical resistance
• Gap-filling formulations available
• Defined processing windows

Limitations:

• Standard formulations are comparatively brittle – peel/impact strength can be improved using toughened types
• Limited adhesion to PE/PP/PTFE
• Transparent epoxies may yellow under UV light

Quality and storage

To ensure quality and shelf life, adhesives should always be stored in a cool, dry place and kept tightly sealed. Direct sunlight should be avoided, and the components should be stored separately. Take care to avoid moisture both on the substrates and in the surrounding environment. Cartridges should be resealed immediately after use to ensure shelf life. Before application, it is advisable to check the viscosity, pot life and workability at the current temperature. A test bond can help to confirm the suitability of the material.

Practical tips

To ensure a consistent joint thickness, the use of microbeads or glass beads is recommended, whilst moderate and even pressure improves the result. Excess material is best removed with a scraper; for a clean finish, the edges can be masked off and finely finished after curing. For optimum adhesion to CFRP or GFRP, it is recommended to prepare the surface with tear-off fabric or to thoroughly sand and clean gelcoat surfaces.

Ensure that the components are conditioned to 20–25°C before bonding and plan for post-curing for high-stress bonds. Always wear gloves and safety goggles and ensure good ventilation, as epoxies can have a sensitising effect. Always refer to the relevant safety data sheet.

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Frequently asked questions (FAQ) about epoxy adhesives

Does epoxy adhesive bond to CFRP/GRP, metal and wood?

Yes, epoxy adhesives are ideal for these substrates. A clean, dry, roughened and degreased surface is required. On PE/PP/PTFE, adhesion is insufficient without special pre-treatment.

What bond joint thickness is recommended?

For film-forming bonds, 0.1–0.3 mm; for gap-filling applications with thixotropic pastes, up to approx. 1 mm. The thickness can be defined using microspheres/spacers.

How do I increase the temperature resistance of the bond?

Select the appropriate system and temper it after room curing (e.g. 40–60 °C). This increases the glass transition temperature (Tg) and long-term stability.

How do epoxy and PU adhesives differ?

Epoxy: structural, high shear strength, rigid; PU: generally more flexible, better peel/impact resistance, some are moisture-curing. Selection depends on the load and substrate.

Are epoxy adhesives suitable for repairs and inserts?

Yes. Thixotropic 2-component pastes are gap-filling and dimensionally stable, ideal for edge builds-up, hole repairs and setting inserts in CFRP/GRP or wood.

Is Epoxy a Glue or Adhesive?

Epoxy is both — and more. While conventional glues rely on mechanical interlocking or simple surface bonding, epoxy adhesives form a true chemical bond with many substrates. They are classified as structural adhesives, meaning they are engineered to withstand significant mechanical loads. Epoxy adhesives are two-component (2K) systems that must be mixed before use and cure through a controlled chemical reaction rather than simply drying.

Is Epoxy Stronger Than Glue?

Yes, in most cases epoxy is significantly stronger than conventional glue. Standard adhesives (such as PVA, hot glue, or contact cement) are generally not suited for load-bearing applications. Epoxy adhesives, by contrast, offer high shear strength and compressive strength, excellent adhesion on demanding substrates, and — when toughness-modified formulations are used — improved peel resistance and impact strength as well. The exact performance depends on the formulation, surface preparation, and curing conditions.