Silicone Condensation 35 A-Component – Medium-Hard Casting Silicone for Concrete Moulds & Plaster Moulds

Premium Medium-Hard Condensation Casting Silicone for Professional Concrete Mould and Plaster Mould Applications

Silicone Condensation 35 A-Component is the base component of a medium-hard 2-component casting silicone based on polycondensation (tin-cure, RTV-2) that cures at room temperature. Once cured, the white silicone is flexible and very strong, with a hardness of Shore A 35 to 37 (with B 5) and a tensile strength of 52 kg/cm². With a viscosity of 21,000 mPa·s (with B 5) the material flows well and captures fine detail. The mixing ratio is 100:5 by weight (with B 5, T 21 or T 51), the working time 30 to 40 minutes and the demoulding time 16 to 20 hours with B 5. Linear shrinkage is less than 0.3%. Ideal for sturdy moulds for concrete, plaster and cement and for heavy, detailed objects.

Please note: this is the A-component only. The B-component (curing agent) must be ordered separately. For standard use we recommend Condensation B 5.

Key Benefits

• Medium-hard with Shore A 35-37: – the mould is sturdy and dimensionally stable, even with heavy casting materials such as concrete and plaster (Shore A 33-35 with T 21 or T 51).
• High tensile strength of 52 kg/cm² (5.10 MPa): – strong moulds for casting heavy and detailed objects.
• Tear strength of more than 25 kg/cm (2.45 N/mm): – the mould resists tearing well at edges and undercuts.
• Good flow at 21,000 mPa·s: – the silicone flows into detail and accurately reproduces surface textures (19,000 mPa·s with T 21 or T 51).
• Low linear shrinkage of less than 0.3%: – castings stay dimensionally accurate to the original.
• Simple 100:5 mixing ratio by weight: – mix by hand or mechanically, with a choice of four B-components for working speed and casting material.

Typical Applications

• Concrete moulds for decorative concrete, garden ornaments and precast decorative elements
• Plaster and cement moulds for detailed and heavy objects
• Ornament moulds for restoration and architectural decoration
• Soap and candle moulds that need extra dimensional stability
• Moulds for polyester (with T 51) or epoxy and polyurethane (with T 21)
• Acrylic resin moulds for sculptures and decorative pieces

Choosing the B-Component (Curing Agent)

The B-component determines the working time, the demoulding time and which casting material is best processed in the mould. Values at 20 °C and 50% relative humidity:

• Condensation B 5 (5%): – standard curing agent; working time 30-40 minutes, demould after 16-20 hours, full strength after 3-4 days, Shore A 35-37, elongation more than 200%, tensile strength 52 kg/cm².
• Wacker Catalyst T 21 (5%): – recommended for casting epoxy and polyurethane; working time over 120 minutes, demould after 48 hours, full strength after 7 days, Shore A 33-35, elongation more than 400%, tensile strength 50 kg/cm².
• Wacker Catalyst T 51 (5%): – recommended for casting polyester; working time over 120 minutes, demould after 48 hours, full strength after 7 days, Shore A 33-35, elongation more than 400%, tensile strength 50 kg/cm².
• Wacker Catalyst T 47 (1-2%): – for very fast work; working time 5 minutes, demould after 0.5 hours, full strength after 1 day, Shore A 35-37, elongation more than 200%, tensile strength 51 kg/cm².

Wacker T 47 may be mixed with the other B-components to achieve a working speed of your choice, while retaining the properties of that B-component. Wacker T 21, T 51 and T 47 can only be ordered by business customers.

Processing Instructions

1. Stir the A-component thoroughly in its container so that the material is homogeneous.
2. Weigh A and B accurately by weight: 100 grams of A to 5 grams of B 5, T 21 or T 51, or 100 grams of A to 1 to 2 grams of T 47. You can use 0.5% more or less curing agent: less curing agent gives a longer cure and more time for air bubbles to escape; more curing agent gives a faster cure but also faster ageing and more shrinkage of the mould. Never use too little curing agent, otherwise the silicone may not cure (properly).
3. Mix A and B thoroughly by hand or mechanically until a homogeneous mixture is obtained, scraping the sides and bottom of the mixing cup.
4. Optional: degas the mixture under vacuum to remove entrapped air.
5. Pour the mixture within the working time (30 to 40 minutes with B 5) and never mix more than you can process within that time.
6. Only demould once the silicone has fully cured: 16 to 20 hours at 20 °C and 50% relative humidity with B 5; full strength after 3 to 4 days. Working time and demoulding time depend strongly on the mixing ratio and humidity: more curing agent or higher humidity shortens both.

Brushing, Spreading or Spatulating

If you want to brush, spread or spatulate the silicone, add 0.6 to 2% Thixo C (usually 1%). This thickening agent makes the silicone spreadable. A brushed or spatulated mould must be fitted with a support jacket, for example made of plaster bandage, an epoxy support jacket or acrylic resin with thickener and glass fabric.

Storage and Shelf Life

Store the silicone in a tightly closed container in a dry, cool, frost-free and well-ventilated place. Under these conditions the shelf life is at least 1 year.

Silicones and More, specialist in high-quality mould rubbers and casting materials for professional makers.

Professional Support

Our specialists help you choose the right B-component for your casting material and build sturdy moulds for concrete, plaster and ornaments. Contact us at info@siliconesandmore.com for advice on the right B-component, mixing ratios and building your mould.