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WHAT GOES INTO EVERY CASTAWAY MOULD
We believe you have the right to know exactly what your tools are made from. This page covers the silicone we use, where it comes from, why we chose it, and everything else you'll need to get the best from your Castaway mould.
THE SILICONE
PLATINUM-CURE RTV SILICONE — EU & UK SOURCED
Castaway moulds use platinum-cure RTV (room temperature vulcanising) silicone, sourced exclusively from established EU and UK manufacturers. Not the cheapest option available — deliberately.
Premium platinum silicone from verified EU and UK sources comes with consistent Shore hardness between batches, full traceability from raw material to finished mould, and a quality standard that cheaper alternatives cannot reliably match.
We know exactly where our silicone comes from, who made it, and what's in it. That means you do too.
Silicone type
Platinum-cure RTV
The premium standard — not tin-cure
Curing system
Addition cure
No by-products, negligible shrinkage
Shrinkage
<0.1%
Tin-cure averages 1–3%
Expected lifespan
100+ casts
Tin-cure: 20–30 casts
Origin
EU & UK
Fully traceable supply chain
Compatibility
Jesmonite · Concrete · Resin · Plaster
Water-based and solvent-based
WHERE IT COMES FROM
THE CASTAWAY SUPPLY CHAIN
Every component in a Castaway mould is traceable from source to your door. This is not marketing language — it's an operational commitment that affects every purchasing decision we make.
01
EU & UK — VERIFIED MANUFACTURERPlatinum Silicone
Sourced from established EU and UK RTV silicone manufacturers with documented quality standards and consistent batch performance.
02
UK — BAMBU LAB P2SSupport Frames & Clips
3D-printed in the UK on a Bambu Lab P2S FDM printer using PLA Tough+ filament. Designed and produced in-house — no third-party manufacturing.
03
UK — IN-HOUSE PRODUCTIONMould Making
Every mould is poured, cured, quality-checked, framed, and packed in the UK. No outsourced steps, no unknown processes in the production chain.
04
UK — DIRECT TO YOUDispatch & Delivery
Dispatched directly from our UK base. 3–5 day delivery as standard. You're buying from the manufacturer — not a reseller, not a middleman.
WHAT TO CAST WITH
COMPATIBLE CASTING MATERIALS
Castaway moulds are compatible with all major casting materials. Here's how each one behaves with our platinum silicone.
Jesmonite AC100
RECOMMENDED
Our primary recommendation. Jesmonite AC100 is water-based, non-toxic, and produces exceptional surface detail. Mix at 2.5:1 (powder:liquid) by weight. Use our calculator for exact quantities. Compatible with all pigments, aggregates, and the AC730 topcoat for water resistance.
Supplier
Polysil — UK distributor for Jesmonite
Concrete
COMPATIBLE
Standard concrete and purpose-mixed casting concrete both work well. Vibration is especially important — use a plate for the full 90 seconds to prevent honeycombing. Expect longer cure times. Finished pieces will be significantly heavier than Jesmonite equivalents.
Best for
Large planters, architectural pieces, outdoor use
Resin
COMPATIBLE
Epoxy and polyurethane resins are fully compatible with platinum silicone — platinum silicone releases resin cleanly without a release agent in most cases. Note that some resin formulations generate heat during cure; ensure adequate ventilation.
Note
Check resin manufacturer's guidance on working temperature and pot life
Plaster
COMPATIBLE
Casting plaster cures quickly and is the most affordable testing material. Ideal for trialling a mould before committing to Jesmonite. Plaster pieces are fragile without sealing. Cure time is 30–60 minutes.
Best for
Prototyping, colour testing, decorative pieces
Ciment Fondu
ADVANCED
A high-alumina cement that produces a distinctive dark, almost black finish with exceptional strength. More technically demanding — requires careful water ratio control. The most architecturally interesting of all casting materials for the Castaway range.
Note
Advanced material — research cure inhibition before first use
Tin-cure silicone
NOT COMPATIBLE
Never use tin-cure silicone in contact with platinum silicone moulds. Tin-cure residue causes cure inhibition — the platinum mould surface will remain tacky and fail to cure. This contamination is permanent and irreversible.
Warning
Keep tin-cure and platinum silicone completely separate — different bowls, tools, and work surfaces
EQUIPMENT
TOOLS YOU'LL NEED
A short and honest list of what you actually need to get great results — with no unnecessary upselling.
Vibration Plate
ESSENTIAL FOR BEST RESULTSThe single biggest investment you can make in your casting quality. Any hobbyist vibration plate in the £30–£80 range will work — the Castaway frame sits stably on all standard plate sizes.
Digital Scales
ESSENTIALJesmonite and concrete mixes must be weighed accurately. Kitchen scales accurate to 1g are sufficient for small and medium moulds. For large moulds, a scale with a 2kg+ capacity is needed.
Mixing Containers & Spatulas
ESSENTIALFlexible silicone mixing bowls are ideal — they allow you to flex the bowl to remove dried material. Use a separate bowl for each colour. Never reuse a bowl contaminated with tin-cure silicone.
Castaway Jesmonite Calculator
RECOMMENDEDOur free online tool gives exact AC100 quantities for every mould in the Castaway range. Available in standard and terrazzo modes. No registration required.
Jesmonite AC730 Topcoat
RECOMMENDEDThe gold standard sealant for Jesmonite pieces. Two to three coats on the interior of bowls and planters provides excellent water resistance. Apply with a foam brush and allow full dry time between coats.
Foam Brushes & Pigments
OPTIONALFoam brushes for topcoat application. Jesmonite-compatible pigments from any reputable supplier work well. Start with no more than 5% pigment by weight of the total mix.