Premium Adhesion-Promoting Primer for Professional Moulding and Encapsulation Applications

ELASTOSIL® AUX G 3243 is a solvent-based primer made from siloxanes and reactive silanes that serves as an adhesion promoter between substrate and vulcanised silicone rubber. The yellow, liquid primer has a density of 0.85 g/cm³ (23°C), a solids content of around 23% and a viscosity of 550 mm²/s. It pre-treats metal, ceramic, glass and various polymer surfaces so that solid ELASTOSIL® R silicone rubber (HCR/HTV, peroxide-curing) adheres durably to them. After the solvents evaporate, a rigid silicone resin film forms on exposure to atmospheric humidity, bonding firmly to a wide range of substrates. The primer can be applied undiluted or diluted up to 1:10 by coating, dipping, brushing or spraying, making it broadly suitable for moulding and encapsulation applications.

Key Benefits

• Broad substrate adhesion – bonds to metal, ceramic, glass and various polymers, enabling the bonding and encapsulation of diverse components.
• Thin working layer of 1–10 µm (5–50 g/m²) – a minimal layer thickness is enough for a reliable adhesion bridge, keeping consumption low.
• Dilutable up to 1:10 – with white spirit or ISOPAR® E, adjustable to the desired application method and layer thickness.
• Solids content around 23% – after the solvents evaporate, a thin, rigid silicone resin film remains as the adhesion layer.
• Multiple application methods – suitable for coating, dipping, brushing and spraying, so processing fits the production line.
• Optional heat post-treatment 100–150°C – increases adhesion on difficult substrates such as smooth metals.

Typical Applications

• Pre-treatment of metal parts before applying ELASTOSIL® R silicone rubber.
• Adhesion bridge on ceramic and glass in technical silicone applications.
• Encapsulating and bonding polymer substrates with solid silicone rubber.
• Preparation of smooth or hard-to-bond surfaces via a thin primer layer.
• Production of technical rubber components requiring durable substrate-to-rubber adhesion.

⚠️ Caution: highly flammable. ELASTOSIL® AUX G 3243 has a flash point of 7°C. From this temperature, flammable vapours may form. Keep away from heat, sparks and open flames, do not smoke and take measures against static electricity.

Processing Instructions

1. Thoroughly clean all substrates with solvents (e.g. white spirit followed by ethanol or acetone); make sure the surface is dry, clean and grease-free.
2. Roughen very smooth surfaces by grinding or blasting; allow metals several hours after cleaning to regenerate their oxide layer.
3. Stir the primer thoroughly before use; dilute if necessary up to a maximum of 1:10 with white spirit or ISOPAR® E.
4. Apply as thin a layer as possible (1–10 µm, i.e. 5–50 g/m²) by coating, dipping, brushing or spraying.
5. Allow the solvent to evaporate for at least 2 hours at room temperature and moderate humidity until a consistent primer film has formed.
6. Apply the silicone rubber preferably soon afterwards, but no later than 2 days. Optionally, heat the primed substrate after solvent evaporation to 100–150°C for up to 1 hour for stronger adhesion.
7. Always carry out preliminary trials; the final adhesion is determined by substrate, silicone type and processing parameters and reaches its maximum only after a few days.

Storage and Shelf Life

ELASTOSIL® AUX G 3243 is moisture-sensitive. On contact with moisture the primer becomes turbid and its adhesive strength decreases. After use, store the primer in a tightly sealed container, cool (10–25°C) and out of direct sunlight. Stir or shake thoroughly before each use. Shelf life is at least 1 year in the unopened original packaging.

About the Manufacturer

Wacker Chemie AG is a world market leader in the development and production of silicones for industrial and technical applications.

Professional Support

Unsure about the right primer or processing method for your substrate and silicone type? Our team is happy to advise on adhesion, pre-treatment and trial setup. Feel free to contact us for personal advice.