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Silastic™ S Kit (4250 Base & Curing Agent)

SKU: SIL34882

Size: 22kg Kit (20kg Base + 2kg Curing Agent)
Sale price


Silastic S RTV 4250 is an addition cure silicone. It is a high-strength silicone mould-making rubber with very low shrinkage and high tear resistance, ideal for detailed reproduction of surfaces and objects for prototype design and production tooling, as well as artistic and renovation applications. Its low durometer also makes it ideal for pad print applications.

A range of materials can be cast into the cured silicone mould including plaster, Jesmonite, concrete, polyurethane, polyester and other reactive resins.

Silastic S comes in a kit form with the Base and Curing Agent (catalyst). The curing agent is green to assist with correct and thorough mixing.

Features & Benefits

• Mix Ratio: Base to Curing Agent = 100 to 10 by weight

• Outstanding release properties

• If required the product cure can be heat accelerated

• Fast thick section cure at room temperature

• Medium hardness

• High inhibition resistance

• High tear resistance

• Very high elasticity, for easy removal of complex replica parts

• Very low shrinkage and good dimensional stability

• Can be used for high temperature casting applications

• Can be made thixotropic (non-flowable) for vertical surface replication

• Fast RTV cure, very fast cure with even, low heat

• Very low viscosity for easy mixing and de-airing

• Fast, RTV cure

• Low durometer hardness


  • Mixed Viscosity: 13,500 mPa.s
  • Working Time: 40-60 Minutes
  • Curing Time: 7 Hours
  • Hardness: 25 Shore A
  • Tensile Strength: 7 MPa
  • Elongation at break: 850%
  • Tear Strength: 23 kN/m
  • Relative Density: 1.12
  • Linear Shrinkage: < 0.1%

Please Note: All addition-cure silicone elastomers are susceptible to cure inhibition when in contact with certain materials and chemicals. Mixing containers, mould construction materials, masters and release agents should be checked for any inhibition effect before use by properly mixing base and curing agent and applying a small amount against the surfaces. Inhibition has occurred if the elastomer is only partially cured after 16 hours, or has a sticky surface in contact with another material. Amines and sulfur-containing materials are strong inhibitors, as are organotin salts used in condensation-cure silicones. Wet or moist surfaces can cause gas bubbles to form during cure in the silicone adjacent to the substrate surface.

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