Premium shrinkage-free addition-cure silicone for professional mold making and casting resin applications

Wacker Elastosil® M 4642 A/B is a pourable, addition-curing (platinum cure) two-component silicone rubber (RTV-2) that cures shrinkage-free at room temperature. The silicone has a dark red final color, an average hardness of Shore A 37, and a mixed viscosity of approximately 15,000 mPa·s, allowing the material to flow well and accurately reproduce fine details. With a pot life of 90 minutes and a cure time of 12 hours at 23°C (can be accelerated with heat), a mixing ratio of 10:1 (A:B) by weight, and a linear shrinkage of less than 0.1%, this material is ideally suited for dimensionally accurate reproduction. Its exceptional resistance to common casting resins makes it the standard choice for molds of models with undercuts.

Key Benefits

• Tear strength >30 N/mm – withstands strong undercuts and repeated demolding without tearing
• Linear shrinkage <0.1% – dimensionally accurate, true-to-size copies thanks to addition curing
• Tensile strength 7 N/mm² – high mechanical load capacity for long-term mold use
• Elongation at break 480% – flexible enough to demold complex geometries
• Shore A 37 – average hardness with sufficient inherent stiffness for dimensionally stable molds
• Mixed viscosity approx. 15,000 mPa·s – very good flow and detailed reproduction

Typical Applications

• Molds for casting polyurethane, polyester, and epoxy resins
• Prototyping and small series production via vacuum casting
• Reproduction of models with strong undercuts requiring dimensional accuracy
• Composite molding and vacuum bagging for composite materials
• Reproduction of art and museum objects with high detail fidelity
• Molds where inherent stiffness of the form is desired

Processing Instructions

1. Stir component A and component B thoroughly and separately first. The platinum catalyst is in component B.
2. Ensure that component A and B have the same lot number, then mix in a weight ratio of 10 parts A to 1 part B.
3. Mix slowly and carefully using a figure-8 motion to avoid introducing air; also scrape the walls and bottom of the mixing vessel.
4. Preferably degas the mixture under vacuum to remove air bubbles.
5. Pour within the 90-minute pot life in a thin stream and from a low height into the mold.
6. Allow to cure for 12 hours at 23°C. Curing can be accelerated with heat; note that air bubbles will then have less time to escape and the Shore hardness may be slightly higher.
7. Optionally, after demolding, post-cure for 2 to 3 hours at 100°C to completely degas the mold.

Please note: pot life and demolding time are highly temperature-dependent. At higher temperatures, both are shorter.

Inhibition Warning

This is an addition-curing (platinum cure) silicone. Curing can be inhibited (inhibition) by sulfur and sulfur compounds, amines and amine-containing substances, organotin and organometallic compounds, and certain plastics. These substances are found in many latex gloves, some plasticines, lacquers and glues, condensation silicones, 1-component silicone sealant, natural rubber, and 3D printing materials (especially stereolithography). If in doubt about gloves, spatulas, cups, or the model, always perform a small test first. If you still want to use an inhibitory surface, apply a release layer of polyvinyl alcohol.

Shelf Life

Store the silicone in a sealed container between 5°C and 25°C. The shelf life is indicated on the packaging.

Professional Support

Wacker Chemie AG is a global market leader in the development and production of silicones for industrial and technical applications. Do you have questions about the right silicone choice for your mold-making or casting resin application? Contact Silicones and More; we are happy to assist you.