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Guide: making a one-part pour or trowel mould (stone strip)
Making a one-part pour or trowel mould (stone strip)
With this guide you make a one-part silicone mould of a decorative stone or stone strip. You work with two layers of condensation silicone C-20: a thin contact layer for the detail and a thickened support layer for rigidity.
📄 Download this guide as PDFWhat are you going to make?
You make a flexible one-part silicone mould to copy a stone strip or decorative stone, for example in Acrystal or acrylic resin. The mould captures every detail of the original, including the surface texture.
Fig. 1 – A decorative stone prepared for copying. Irregularities have been filled and the stone has been treated with a release agent.
💡 Never mix the silicone for both layers at once. By the time you apply the second layer, the first portion will largely have cured in the pot.
Required materials
🛒 From the webshop
🧰 Supply yourself
- Scale
- Mixing container
- Stir stick or spatula
- Brush
- Release agent (for porous or sticky models)
- Colorant for the B component (optional, to check mixing)
Processing data
| Property | Value |
|---|---|
| Mixing ratio C-20 | A : B = 100 : 2 (2% B by weight) |
| Variation B component | 1.5 to 3% (recommended 2%) |
| Thixo C contact layer | 0.01% (1 drop per 100 grams) |
| Thixo C support layer | 0.6 to 2% (recommended 0.6%) |
| Contact layer thickness | around 0.5 mm |
| Total mould thickness | around 0.5 to 1 cm |
| Demoulding possible after | around 8 hours |
| Full strength after | 3 days |
Preparation
Make sure the model is clean. Remove dirt, dust and unwanted irregularities, because the mould captures every detail. Glossy areas come back glossy in the mould, matte areas stay matte.
Treat the model with a release agent if needed. Treat fresh plasticine or clay with a sealer so the silicone does not contact the porous surface, preventing adhesion and air bubbles.
⚠️ Mind the pot life of the silicone: the working time is around 1 hour. Lay out all materials before you start.
Mix the contact layer (layer 1)
Pour the required amount of Silicone C-20 A into a roomy pot, enough to give the whole model a thin 0.5 mm film. Add 2% Silicone C-20 B in the correct ratio (by weight).
Mix very well with a stir stick, going carefully along the edges of the pot; where the components are not well mixed, the silicone will not cure. Optionally add a colorant to the B so you can see whether everything is mixed evenly.
Now add a very small amount of Thixo C: 0.01%, or one drop per 100 grams. Mix thoroughly again.
⚠️ The contact layer determines the quality of the mould. Do not trap air bubbles, dust particles or other irregularities.
Apply the contact layer
Take a brush or spatula and coat the entire model with a thin layer of silicone. Aim for a film around 0.5 mm thick. Do not apply this layer too thick, so air bubbles can escape easily.
Let everything rest for 1 to 2 hours so the silicone can partly cure.
Mix the support layer (layer 2)
Pour the required amount of Silicone C-20 A into a roomy pot again and add 2% C-20 B. Then add 0.6 to 2% Thixo C; 0.6% is recommended (at 2% the silicone becomes more viscous).
Mix firmly and thoroughly. Let the mixture rest for a few minutes so the Thixo can do its work, then stir gently once more.
⚠️ Apply the second layer while the first is still tacky (sticky, not fully cured). This creates a good chemical bond between the two layers.
Apply the support layer
Spread the silicone onto the model, making sure not to brush in air bubbles. Press well into the cavities with the brush so no air remains. Build the layer up to a total mould thickness of around 5 mm to 1 cm.
Do not tear the first layer while applying. The silicone is thickened enough when you can apply it 1 to 2 cm thick on a vertical wall with a spatula without it running.
Cure and demould
The silicone is sufficiently cured to demould after around 8 hours. After around 10 hours the mould is ready for use, but the ultimate strength is only reached after 3 days.
Carefully remove the mould from the model. The mould is now ready to make casts with, for example in Acrystal or acrylic resin.
Additional information
- Let the mould cure for around 8 hours before demoulding; final strength is guaranteed after 3 days.
- The percentage of Silicone B determines how fast the silicone cures. You can vary between 1.5 and 3%, 2% is recommended. More than 3% may affect strength.
- Always work with clean material: mixing cup, spatula, mould and tools.
- Treat fresh plasticine or clay with a sealer to prevent adhesion and air bubbles.
- Add colorant to the B component before adding it to A; an even color without white streaks tells you everything is well mixed.
- If you add no Thixo, you can also use the silicone as a pouring silicone.
Storage
Store the C-20 components and Thixo C well sealed, dry and at room temperature. Store the cured mould flat and free of pressure so it keeps its shape and stays reusable.
Frequently asked questions
Why two layers with different amounts of Thixo?
The first layer contains almost no thickener so it flows thin and captures all details and air bubbles perfectly. The second layer is thickened so it stays put and gives the mould strength and thickness.
What does tacky mean?
Tacky means sticky, that is, not yet fully cured. By applying the second layer while the first is tacky, the layers bond chemically into one whole.
Can I also pour this silicone?
Yes. If you add no Thixo, the C-20 stays liquid and you can use it as pouring silicone for a one-part pour mould.
How soon can I use the mould?
After around 8 to 10 hours you can demould and use the mould. For maximum strength and lifespan, wait 3 days.