Wacker Elastosil® M 4642 A/B – Dark Red Addition-Cure Silicone for Moulds & Casting Resins

Premium shrink-free addition-cure silicone for professional mould-making and casting resin applications

Wacker Elastosil® M 4642 A/B is a pourable, addition-cure (platinum-cure) two-component silicone rubber (RTV-2) that cures at room temperature without shrinkage. The cured silicone is dark red, has a medium hardness of Shore A 37 and a mixed viscosity of approx. 15,000 mPa·s, so the material flows out well and reproduces fine detail accurately. With a pot life of 90 minutes, a curing time of 12 hours at 23 °C (can be accelerated with heat), a mix ratio of 10:1 (A:B) by weight and linear shrinkage of less than 0.1%, this material is ideally suited to dimensionally accurate reproduction. Its exceptional resistance to common casting resins makes it the standard choice for moulds of models with undercuts.

Key Benefits

• Tear strength >30 N/mm – copes with deep undercuts and repeated demoulding without tearing
• Linear shrinkage <0.1% – dimensionally accurate, true-to-size copies thanks to addition curing
• Tensile strength 7 N/mm² – high mechanical strength for long-term mould use
• Elongation at break 480% – flexible enough to demould complex geometries
• Shore A 37 – medium hardness with enough inherent stiffness for dimensionally stable moulds
• Mixed viscosity approx. 15,000 mPa·s – excellent flow and highly detailed reproduction

Typical Applications

• Moulds for casting polyurethane, polyester and epoxy resins
• Prototyping and small-batch production by vacuum casting
• Reproduction of models with deep undercuts that require dimensional accuracy
• Composite moulding and vacuum bags for composite materials
• Reproduction of art and museum objects with high detail fidelity
• Moulds where a degree of inherent stiffness is required

Processing Instructions

1. First stir Part A and Part B thoroughly, each separately. The platinum catalyst is in Part B.
2. Check that Part A and Part B have the same batch number, then mix in a ratio of 10 parts A to 1 part B by weight.
3. Mix slowly and carefully in a figure-of-eight motion so that no air is whipped in; also scrape the sides and bottom of the mixing container.
4. Preferably degas the mixture under vacuum to remove air bubbles.
5. Pour into the mould within the 90-minute pot life in a thin stream from a low height.
6. Leave to cure for 12 hours at 23 °C. Curing can be accelerated with heat; note, however, that air bubbles then have less time to escape and the Shore hardness may turn out slightly higher.
7. Optionally, post-cure the mould for 2 to 3 hours at 100 °C after demoulding to degas it completely.

Please note: pot life and demoulding time depend strongly on temperature. Both are shorter at higher temperatures.

Inhibition Warning

This is an addition-cure (platinum-cure) silicone. Curing can be inhibited by sulphur and sulphur compounds, amines and amine-containing substances, organotin and other organometallic compounds, and certain plastics. These substances are found in, among other things, many latex gloves, some plasticines, lacquers and adhesives, condensation-cure silicones, one-component silicone sealants, natural rubber and 3D printing materials (stereolithography in particular). If you are in any doubt about gloves, spatulas, cups or the model, always do a small test first. If you still want to use an inhibiting surface, apply a barrier coat of polyvinyl alcohol.

Shelf Life

Store the silicone in its closed packaging between 5 °C and 25 °C. The shelf life is stated on the packaging.

Professional Support

Wacker Chemie AG is the global market leader in the development and production of silicones for industrial and technical applications. Do you have questions about choosing the right silicone for your mould-making or casting resin application? Contact Silicones and More – we will be glad to advise you.