Brush-on Mould Making
Creating a jacket mould using Mould Master 30
In this guide we will take you step-by-step through the process of making a brush-on silicone mould and rigid support jacket. We’ll look at all the materials you’ll need as well as all the different stages involved.
Key materials required:
• Mould Master 30 Silicone Moulding Rubber
• Mould Master Thixotropic thickening agent
• Mould release agent (e.g, Mouldwax or or Macsil)
Other supplies:
• Sculpting clay or plasticine (for building registration keys and dams)
• Mixing containers and sticks
• Brushes (disposable, suitable for thickened silicone)
• Plaster bandage (or GRP materials: resin, catalyst, chopped strand mat, gloves, etc.)
• PPE: Gloves, apron, safety glasses, respiratory protection for GRP if used
Step-by-Step Procedure
1. Master Preparation
• Secure the master to a flat baseboard using hot glue or double-sided tape
• Ensure the master is clean and free of dust
• Apply an appropriate release agent to the master and surrounding baseboard if the surface is non-porous or has the potential to bond with silicone
2. Building a Clay Wall (Optional)
• For ease and control, a temporary clay wall can be built around the master to control the thickness of the first silicone coat and help avoid undercuts
3. First Coat (Print/Detail Coat)
• Mix Mould Master 30 Part A and Part B at the recommended 10:1 ratio by weight
• Do not add thixo to this first coat
• Brush a thin, even layer of silicone onto the master, working it into all surface details and edges
• Allow this layer to partially cure until tacky before proceeding (approx. 30–60 mins depending on temperature)
4. Build-Up Coats with Thixo
• For subsequent layers, mix fresh batches of Mould Master 30 and add Thixo additive (usually 2–4% by weight) until a non-slump, peanut butter-like consistency is achieved
• Brush on 2–4 additional layers, ensuring even coverage and building to a minimum thickness of 5–10mm overall
• Allow each layer to tack off slightly before applying the next to ensure good interlayer bonding
• Include registration keys made of thickened silicone or clay blobs during final coats to help align the support jacket.
5. Curing
• Allow the silicone to fully cure (typically 12 hours at room temperature; overnight is ideal).
• Once cured, remove any clay supports or temporary walls.
6. Prepare for Support Jacket
• Ensure the cured silicone layer is clean and dry.
7. Support Jacket Options
Option A: Plaster Bandage Jacket
• Wet plaster bandages and apply in overlapping strips across the mould surface.
• Build up to around 10–20mm thickness.
• Allow to set completely (approx. 30–60 minutes).
Option B: GRP Jacket (Glass-Reinforced Plastic)
• Mix polyester resin with the appropriate catalyst.
• Apply a layer of resin followed by layers of chopped strand mat, thoroughly wetting out each layer.
• Build to desired rigidity (usually 2–3 layers is sufficient).
• Allow to fully cure (1–2 hours depending on conditions).
8. Demoulding
• Carefully remove the support jacket.
• Gently peel the silicone mould away from the master, starting at the edges.
• Check for any undercuts or details that may require extra care.
9. Final Inspection and Use
• Inspect the silicone mould for bubbles or thin spots.
• Trim any flashing or unwanted overflow.
• The mould is now ready for use in casting with resins, plasters, waxes, etc.
Safety & Storage
• Always wear appropriate PPE when handling resins and silicones.
• Store silicone and thixo additive in a cool, dry place.
• Clean tools immediately after use.
