Premium Toluene-Free Bonding Primer for Professional Silicone and Industrial Bonding Applications

Wacker Primer G 790 toluene-free is a solvent-based, one-component bonding primer based on reactive silanes and siloxanes. The primer is clear to light yellow, has a density of 0.76 g/cm³ and a kinematic viscosity of 1 mm²/s, with an active substance content of approximately 17%. It is free of toluene and other aromatic solvents. The primer is preferably used with addition-cure silicone rubbers (LSR, XLR® and RTV-2 grades) and promotes a durable chemical bond between the silicone and a wide range of substrates such as metal, glass-fibre-reinforced plastic, wood and various plastics. As the solvent evaporates, a thin primer film forms with the help of atmospheric humidity that adheres firmly to the substrate.

Key Benefits

• ✓ Toluene-free – free of toluene and other aromatic solvents, for a safer processing profile than classic primers.
• ✓ Active substance content 17% – balanced concentration of reactive silanes and siloxanes for a reliable bonding layer.
• ✓ Very thin layer 1–10 µm – at a coating weight of 5–50 g/m², a minimal amount is sufficient, enabling economical and even application.
• ✓ Dilutable to 1:10 – can be diluted with white spirit or ISOPAR® E to improve surface wetting.
• ✓ Low viscosity 1 mm²/s – thin-flowing, suitable for brushing, dipping and spraying.
• ✓ Broad adhesion – suitable for metal, glass-fibre-reinforced plastic, wood, aluminium, polyamide, polyester, polyurethane, acrylate, glass and ceramics.

Typical Applications

• → Bonding layer for addition-cure silicone rubbers (LSR, XLR®, RTV-2) on metal parts and fittings.
• → Pre-treatment of glass-fibre-reinforced plastic (GRP) before overmoulding with silicone.
• → Bonding of silicone to aluminium, steel, lead and iron in industrial constructions.
• → Adhesion to plastics such as PETG, nylon, acrylate, epoxy and PVC.
• → Pre-treatment of wood and ceramics for silicone seals and encapsulations.
• → Applications in insulators, cable accessories and surge arresters in electrical engineering.

Processing Instructions

1. Make the surface to be bonded dry, dust-free and grease-free. Clean first with a non-polar solvent (such as white spirit, boiling range 80–140°C) and then with a polar solvent such as acetone. Very smooth surfaces may be lightly roughened; remove loose particles.
2. After cleaning, allow metals several hours to regenerate their oxide layer before priming.
3. Apply the primer undiluted or diluted (1:1 to 1:10 with white spirit or ISOPAR® E) by brush, dipping or spraying. Apply the layer as thin as possible: 1–10 µm, corresponding to 5–50 g/m².
4. Allow the solvent to evaporate at room temperature. At approximately 40% relative humidity, allow 1–2 hours drying time. At lower temperature or humidity this takes longer.
5. Optionally, adhesion can be improved by heating the primed surface to 100–150°C for up to one hour after drying.
6. Apply the silicone preferably within 5 hours of priming. After that, adhesive strength may decrease. Keep the primed surface free of contamination until then.
7. The primer usually provides good adhesion immediately after vulcanization; maximum adhesive strength is in many cases only reached after about 4 days.

Shelf life: at least 1 year, provided it is stored between 10 and 25°C, dry and protected from direct sunlight. The primer is moisture-sensitive; close the container tightly after use.

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

Professional Support

Unsure whether this primer is suitable for your specific combination of silicone and substrate, or about the correct dilution and processing? Please contact us. Our specialists are happy to advise you on the best bonding solution for your application.