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LEARN · TECHNIQUE GUIDES
HOW TO GET FLAWLESS RESULTS EVERY TIME
From preparation to demoulding, finishing to storage — everything you need to cast with confidence using your Castaway mould.
WHAT THIS GUIDE COVERS
Preparing your material
Vibration plate technique
Surface finishes
Demoulding & cleaning
Jesmonite calculator tool
THE TECHNIQUE
STEP BY STEP — FROM POUR TO FINISHED PIECE
Follow this process consistently and your results will improve with every single cast.
01
ASSEMBLE & CHECK THE MOULD
Fit the silicone into the frame halves and lock the speed clips. Check that the clips are fully seated — they should click firmly into place. Give the assembled mould a gentle squeeze. If there's any flex or gap, check the clip orientation and re-seat. A correctly assembled mould will feel solid and rigid.
02
CALCULATE & PREPARE YOUR MATERIAL
Use the Castaway Jesmonite Calculator to get the exact quantities for your mould. Mix Jesmonite AC100 at a 2.5:1 (powder to liquid) ratio by weight. Mix for a full 3 minutes, scraping the sides of the bowl. The mix should be smooth, lump-free, and pour like thick cream.
03
POUR SLOWLY FROM ONE CORNER
Tilt the mould slightly and pour from the lowest corner. A slow, controlled pour flowing across the mould surface introduces far fewer air bubbles than pouring directly into the centre. Pour until the mould is filled to approximately 2–3mm from the top rim.
04
VIBRATE — 60 TO 90 SECONDS
Place the filled mould on your vibration plate immediately after pouring. Run for 60–90 seconds. You'll see air bubbles rising to the surface and popping — this is exactly what you want. The rigid Castaway frame sits flat and stable on the plate throughout.
05
CURE — DO NOT RUSH
Leave the mould undisturbed at room temperature (18–22°C) for a minimum of 24 hours. The surface should be firm to the touch and no longer tacky before demoulding. Rushing this step is the most common cause of cracking, tearing, and poor surface quality.
06
DEMOULD CLEANLY
Remove the speed clips. Open the frame halves. The platinum silicone will peel away from the cast without force. Wipe the silicone with a damp cloth immediately. Refit the frame for storage.
CASTAWAY WORKSHOP TOOL
JESMONITE CALCULATOR
Take the guesswork out of your mix. Our Jesmonite calculator gives you exact powder and liquid quantities for every Castaway mould — with or without pigment.
OPEN THE JESMONITE CALCULATOR
Enter your mould, select your finish, and get exact AC100 quantities in seconds. Available in standard and terrazzo modes. No registration required.
PROFESSIONAL TECHNIQUE
WHY YOU NEED A VIBRATION PLATE
A vibration plate is the single biggest upgrade you can make to your casting results. Every Castaway mould is engineered specifically to sit stably on a vibration plate — the rigid frame makes this possible.
Without vibration, air bubbles trapped in your mix become voids in your finished piece. With 60–90 seconds of vibration, the vast majority are eliminated.
01
POUR FIRST
Fill the mould as normal, then move it immediately to the vibration plate while the mix is still fluid.
02
RUN FOR 60–90 SECONDS
You'll see bubbles rising to the surface. The frame keeps everything stable throughout.
03
LEAVE TO CURE UNDISTURBED
Once vibration is complete, move to a level surface and leave. No further intervention needed.
FINISHES & EFFECTS
WHAT YOU CAN MAKE WITH YOUR CASTAWAY MOULD
Castaway moulds are compatible with Jesmonite AC100, concrete, plaster, and resin. Here's how different finishes and techniques interact with the mould.
PLAIN JESMONITE
CLEAN · ARCHITECTURAL · VERSATILE
Plain AC100 in white or pigmented colours captures mould detail with exceptional precision. The ribbed, faceted, and twisted surfaces in the Castaway range look particularly strong in a single solid colour where the form is the focus.
TERRAZZO
BOLD · TEXTURED · DISTINCTIVE
Add aggregate to your Jesmonite mix before pouring. The vibration plate is especially valuable for terrazzo — it settles the aggregate evenly and brings trapped air to the surface. The Ribbed Bowl and Incense Holder are particularly striking in terrazzo.
MARBLED / SWIRL
ORGANIC · UNIQUE · PREMIUM
Mix two or more colours and pour them together without fully combining. Each cast is unique. The Swirl Pot is designed to emphasise this technique — its spiral interior channels create additional movement in the finished piece.
CONCRETE
INDUSTRIAL · ARCHITECTURAL · MATTE
Standard Portland cement or purpose-made concrete mixes work well with all Castaway moulds. Vibration is essential with concrete to prevent honeycombing. Expect longer cure times of 48–72 hours minimum.
PLASTER
LIGHTWEIGHT · QUICK · AFFORDABLE
Casting plaster is the fastest and most affordable material to work with. It cures in as little as 30 minutes and captures fine detail well. Ideal for testing a mould and colour combination before committing to a more expensive material.
SEALING & FINISHING
PROFESSIONAL RESULTS
Seal Jesmonite interiors with AC730 topcoat for water resistance — two to three coats is sufficient. For a high-gloss finish, wet-sand progressively from 400 to 2000 grit, then apply cutting compound and wax.
PRO TIPS
COMMON MISTAKES AND HOW TO AVOID THEM
DEMOULDING TOO EARLY
The most common error. Jesmonite feels set on the surface long before it has cured fully. Always wait the full 24 hours — cracking and tearing on demould is almost always caused by rushing this step.
SKIPPING VIBRATION
Without vibration, you will get surface pitting from trapped air. If you don't have a plate, tap the assembled mould firmly on the work surface 20–30 times immediately after pouring.
INCONSISTENT MIX RATIO
Jesmonite mixed too wet will be weak and slow to cure. Too dry and it won't flow properly into mould detail. Weigh your components — never estimate by volume.
STORING WITHOUT THE FRAME
Platinum silicone is flexible. Without the frame fitted, the mould can deform over time. Always keep the frame fitted when the mould is not in use.
USING SOLVENT CLEANERS
Solvents and harsh chemicals damage platinum silicone over time. Clean your mould with warm water and mild soap only. Dry thoroughly before storage.
OVERFILLING THE MOULD
Fill to 2–3mm from the rim only. Overfilling creates a thick, uneven base and can cause overflow. A slightly underfilled piece is far preferable to an overfilled one.