Wacker Catalyst T 51® – Curing Agent for ELASTOSIL® M Condensation Silicones & Polyester Casting

Premium condensation catalyst for professional mould making and reproduction applications

Wacker Catalyst T 51 is the standard curing agent (Part B) for the condensation-curing ELASTOSIL® M silicone rubbers, such as Elastosil M 4511, M 4512, M 4514, and M 4541. This reddish-brown, low-viscosity catalyst based on an organotin compound and silicic acid ester has a density of 0.92 g/cm³ and a dynamic viscosity of 50 mPa·s at 23 °C. T 51 has been specifically optimised for excellent chemical resistance to polyester resins, which considerably extends the service life of the mould. The standard dosage is 5% by weight of Part A (100:5 ratio). Less catalyst extends the pot life and demoulding time and allows air bubbles more time to escape; more catalyst accelerates curing but increases shrinkage and mould ageing. At a 5% dosage with Elastosil M 4514, the pot life is approximately 60 to 90 minutes and the demoulding time is 8 to 12 hours at 23 °C and 50% relative humidity.

Key Benefits

• Dosage 5% (100:5) – fixed, easy-to-measure weight ratio to Part A for reliable curing.
• Density 0.92 g/cm³ and viscosity 50 mPa·s – low-viscosity, mixes quickly and evenly with the base component.
• Excellent polyester resistance – significantly extends mould life when casting polyester resins.
• Can be blended with Catalyst T 47 – pot life and demoulding time precisely adjustable; at 95:5 (T 51 : T 47), the pot life drops to approximately 30 minutes, and the mould can be demoulded after approximately 4 hours.
• Reddish-brown colour – provides visual mixing control, so you can see when the catalyst is evenly distributed.
• Long shelf life – can be stored stably, even in larger quantities, provided it is kept dry and cool.

Typical Applications

• Curing Elastosil M 4511, M 4512, M 4514, and M 4541 condensation silicones.
• Mould making for casting polyester resins.
• Reproduction moulds for plaster, concrete, and artificial stone.
• Moulds for wax, candles, and low-melting metal alloys.
• Blending with Catalyst T 47 for accelerated curing in time-critical production.

Processing Instructions

1. Stir the condensation silicone (Part A) thoroughly before use to distribute any sedimentation.
2. Weigh out the catalyst at 5% of the weight of Part A, i.e. 5 grams of T 51 per 100 grams of silicone. You can use 0.5% less or more: less extends curing (more time for de-aeration), more accelerates it but increases shrinkage. Never use too little catalyst, otherwise the silicone will not cure (properly).
3. For faster curing, you can blend T 51 with Catalyst T 47, for example in a 95:5 ratio (per 100 grams of Part A: 4.75 grams of T 51 with 0.25 grams of T 47).
4. Mix the catalyst carefully and evenly into the silicone until the colour is uniform.
5. Process the mixture within the pot life and never prepare more than you can process within that time.
6. Wait until the mixture is fully cured before demoulding.

Note: pot life (working time) and demoulding time are highly dependent on the mix ratio and humidity. With more catalyst or higher humidity, both pot life and demoulding time will be shorter. Below 40% relative humidity, the silicone surface may remain tacky; in this case, increase the humidity in the room.

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

Shelf life: if stored in sealed packaging, dry and cool, the shelf life is at least the period stated on the label. Exceeding this does not automatically render the product unusable; check its properties before use.

This product is intended for business customers. For larger quantities or customised products, please contact us at info@siliconesandmore.com.

Professional Support

Are you unsure about the correct dosage or blending with T 47 for faster curing? Our specialists are happy to advise you on the best catalyst combination for your application. Feel free to contact us.