How to Cast Concrete Using Silicone Moulds (Step-by-Step Guide)
- Astrid van Essen
- 2 days ago
- 5 min read
Concrete casting is a brilliant way to create beautiful, durable home accessories like planters, trays, and incense holders. Whether you buy a ready-made silicone mould or make your own, the process is surprisingly accessible — and the results can look just as polished as store-bought décor.
At Botanical Blueprint, we use ready-made silicone moulds and make our own to achieve unique shapes and textures. Using a pre-made mould is a great way to begin if you're starting.
Note: Some of the links in this post are affiliate links. This means if you click through and make a purchase, I may earn a small commission at no extra cost to you. I only recommend products I’ve used or believe will add value to your projects.
Should You Buy a Silicone Mould or Make Your Own?
Buying Ready-Made Moulds
Pre-made silicone moulds are ideal for beginners. They come in all sorts of shapes and sizes, from minimalist trays to quirky planter designs, and they’re designed to handle the weight and texture of concrete. Look for moulds that are:
Thick-walled and durable
Labelled for use with concrete or casting materials
Flexible enough to release the piece easily
Making Your Silicone Moulds
Making your mould is worthwhile if you have a specific shape in mind or want to replicate an object. It allows for creative freedom and helps you stand out if you create pieces to sell.
You’ll need a ‘master’ (the object you want to replicate), a sturdy container to hold the silicone, and good-quality moulding silicone. This method is more hands-on but offers total control over design and sizing.
Recommended Silicone Brands for DIY Mould Making
If you’re planning to make silicone moulds, here are some reliable brands to try:
Smooth-On (Mold Star 15 or OOMOO 25) – Easy to mix, great for detail, widely used by makers
Polycraft (GP-3481 or Silskin) – UK-based, cost-effective, suitable for general moulding
Tomps Silicone Rubber – Offers brush-on and pourable options, with thickeners available
What to Look For
Mix Ratio – 1:1 mixes are easiest for beginners.
Working Time – Go for a silicone that gives you at least 10–20 minutes to pour
Shore Hardness – Shore A 20–30 is ideal for most decorative concrete work
Curing Time – Choose a fast-curing product if you want quicker turnaround (1–24 hours)
Tips for Beginners
Start Small – Try moulding a tealight holder or a coaster first
Seal Porous Masters – Use shellac or clear sealant to prevent sticking
Pour Slowly – A thin stream helps avoid air bubbles
Support Your Mould – Use a tray or box to prevent silicone from warping
Use a Release Agent – Even with silicone, this helps prolong mould life and ease demoulding
Release Agents for Concrete & Silicone Moulds
1. Smooth-On Universal Mould Release
Type: Spray
Best For: Silicone, latex, polyurethane moulds
Why It’s Good: Industry-standard, easy to apply, works with both silicone and concrete
Type: Aerosol spray
Best For: Concrete casting, especially with silicone or polyurethane moulds
Why It’s Good: Creates a consistent, dry film — ideal for repeatable clean releases
Type: Spray (available in 400ml cans)
Best For: Silicone rubber moulds used with plaster, concrete, or resin
Why It’s Good: UK-based and formulated for concrete applications
Type: Multi-purpose silicone spray
Best For: Light-duty use with concrete, resin, and rubber
Why It’s Good: Budget-friendly option, but may need more frequent application for detailed work
Type: Professional mould release
Best For: Highly detailed concrete or resin casting
Why It’s Good: Excellent results, though more expensive — good for complex or commercial use
Step-by-Step: How to Cast Concrete Using Silicone Moulds
1. Prepare the Master and Mould Housing
If you’re making your mould, place your master in a container (like a cut bottle or mould box) to hold the silicone around it.
2. Apply Release Agent (Optional but Recommended)
Spray the master and container lightly with mould release spray, especially if the master is porous.
3. Mix and Pour the Silicone
Mix according to the manufacturer’s instructions. Pour slowly into one corner, allowing the silicone to rise and surround the item without trapping air.
4. Let It Cure and Remove the Silicone
Let the silicone set completely. Curing time varies between 1 to 24 hours. Once cured, remove the mould housing and gently peel the silicone from the master.
5. Set Up for Concrete Casting
Place your silicone mould in a supportive tray or frame to keep its shape. If desired, apply a light coat of release agent.
6. Mix and Pour the Concrete
Mix your concrete to a pourable, oatmeal-like consistency. Slowly pour into the mould, tapping gently to remove any trapped bubbles.
7. Allow to Cure and Demould
Leave the concrete to cure for 24–48 hours. Once hardened, flex the silicone to release the cast piece.
8. Clean and Store the Mould
Rinse the mould with mild soap and water. Avoid abrasive tools. Store flat, in a cool and dry place, away from direct sunlight.
Concrete Casting at a Glance
Step | Description |
Prepare Master | Choose or create your item and build a container |
Apply Release Agent | An optional step to protect the mould |
Mix and Pour Silicone | Mix well and pour slowly |
Cure and Demould | Let the silicone set and peel away |
Set Up for Casting | Place the silicone mould in a supportive tray |
Mix and Pour Concrete | Pour concrete and remove air bubbles |
Cure and Demould | Let it set for 1–2 days before removing |
Clean and Store Mould | Wash and store properly for reuse |
Final Thoughts
Silicone moulds make concrete casting easy, repeatable, and creatively fulfilling. Whether you choose the ready-made route or try making your own mould, the key to success is preparation, patience, and practice.
At Botanical Blueprint, we use these techniques to create our concrete home accessories—and with the right tools, you can, too.
Would you like to shop finished pieces or see what goes on behind the scenes? Explore the Botanical Blueprint collection for more.
Frequently Asked Questions
1. Do I need to use a release agent with silicone moulds? Not always, but it’s highly recommended — especially for detailed casts or repeated use. It helps protect the mould and makes it easier to demould without damaging delicate edges.
2. Can I reuse my silicone moulds for concrete casting? Yes, silicone moulds can be reused many times if you clean them properly and store them out of direct sunlight. Regular use of a release spray also extends mould life.
3. What type of concrete should I use for casting? For detailed work, use a fine concrete mix or Portland cement. Standard ready-mix concrete works well for larger, simple shapes. Aim for a smooth, pourable texture—like thick oatmeal.
4. How can I prevent air bubbles in my concrete? Pour slowly in layers and gently tap or vibrate the mould after pouring. This helps trapped air rise to the surface for a smoother finish.
5. How long should I wait before demoulding concrete? Most small to medium casts can be demoulded after 24–48 hours. Always check the hardness before removing. Let the piece cure further outside the mould for maximum strength.
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