Jesmonite is a material prized for how easy it is to work with and for the many creative possibilities it offers. Among the different Jesmonite products available, each one is suited to specific uses, but all of them call for a few adjustments and good habits to achieve perfectly smooth, strong and flawless pieces.
While you are creating, you may come across air bubbles, find that your mix sets faster than expected or that your piece breaks when you demould it. These setbacks are among the most common difficulties when you are starting out with Jesmonite®. Discover their main causes, along with our practical tips for avoiding them and making your creations with greater peace of mind.
Alongside these tips, remember that Jesmonite offers plenty of customisation options. With pigments and the different colouring techniques, you can create objects that perfectly reflect your style.
Air bubbles forming
Are you making, or about to make, your first Jesmonite creations, only to find when you demould them that small bubbles have formed in your mix? Don't worry: here are our tips to stop it happening, or at least to keep it to a minimum.
Why air gets into your mix
Several factors explain this:
- Mixing too vigorously traps air without it being immediately visible.
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Mixing for too long. The longer you mix, the more chances bubbles have to form.
- Adding the powder to the liquid too quickly, or moving the mould during the process, traps air at different levels.
- Failing to work the material into the corners and details right from the start lets air pockets settle unnoticed.
As long as this air remains trapped, it does not go away: it eventually rises to the surface once the piece has hardened, leaving unsightly marks.
A few adjustments make all the difference
Here are the habits to adopt to significantly improve the final result.
When mixing:
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Pour in the liquid first, then the powder.
This prevents dry lumps from forming, so there is no need to keep working the mix to get rid of them. -
Mix gently, without jerky movements.
A steady, controlled motion is enough to blend the mix evenly without adding unnecessary air. -
Choose the right tool for the amount you are preparing.
A spatula is recommended: it lets you blend the mix gently, break up lumps and push out air without overworking it. Avoid using a whisk, as it tends to incorporate more air while mixing. -
Scrape the sides and bottom of the container regularly.
This ensures an even mix and prevents dry patches that would weaken the final texture.
When pouring:
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Pour in a thin stream, always in the same spot.
A natural flow from a single point limits turbulence and stops air from spreading through the material. -
Start with a small amount at the bottom of the mould.
Working the material into the edges and detailed areas from the outset pushes out the air before it becomes a problem. Don't hesitate to quickly apply a first coat to the bottom and sides of the mould.
Once the mould is full:
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Tap or gently vibrate the mould.
This brings any remaining air bubbles to the surface so they can escape before the mix starts to set. -
Opt for a vibrating table.
Our Jesmonite® vibrating plate gently shakes the mould to help bubbles rise and escape. It is particularly useful for detailed pieces or whenever you are aiming for a flawless, professional finish.
My mix is setting too quickly
Fast setting is inherent to Jesmonite. This material naturally hardens quickly, so the best way round it is to work in small batches and move swiftly once the components are combined. You need to work straight away, as the working time is short. That is why it is so important to have everything to hand before you even start mixing: mould, pigments and tools.
What makes it set too quickly?
Several factors can speed up hardening:
- Preparing too large a batch.
- A room that is too warm.
- Taking too long over the preparation.
Reminder: the material starts to set as soon as mixing is complete, so every minute counts.
How to gain working time
Two simple habits buy you more time:
- Plan everything before mixing: your tools, mould and pigments should be ready in advance.
- Only prepare the amount needed for the current pour, without overdoing it.
Good to know: Jesmonite offers set retarders suited to each system, to use if your project needs more leeway.
Jesmonite retarder: extend your working time
The set retarder is an additive specially formulated to increase Jesmonite's working time before it hardens. Available for Jesmonite AC100, AC84 and AC730, it gives you a few extra minutes to mix, colour and pour the material in better conditions, with more comfort and precision as you make your creations.
We offer two retarders:
- The AC100-compatible retarder: extends working time to between 25 and 30 minutes.
- The AC84- and AC730-compatible retarder: extends working time to between 45 and 60 minutes.
My piece breaks when I demould it
Breakage when demoulding is most often caused by demoulding too early or by a piece that is too fragile for the shape of the mould. We recommend waiting until the piece has set sufficiently before demoulding it, while avoiding leaving it in the mould for too long.
Common causes
A thin piece with protruding details or very delicate areas breaks more easily when it is removed. A mix with the wrong ratio, or one that is not blended evenly enough, can also make the object more fragile.
How to reduce the risk
Wait until the piece has set just enough, then demould with slow, steady movements, without forcing the thin parts. We recommend planning a clean, well-thought-out casting from the start, as good preparation makes removal easier and reduces the strain on the piece.
In practice, the best strategy is to stick to the recommended setting time, avoid handling the piece while it is still warm or flexible, and choose less fragile shapes for your first creations.
Master Jesmonite with ease using these tips
The small flaws you come across in your first Jesmonite projects are completely normal and quickly fade with a little practice. By sticking to the right ratios, preparing your equipment in advance and using the right techniques when mixing, pouring and demoulding, you will achieve cleaner, stronger creations with a professional finish. Every attempt will help you refine your technique and gain greater control.
To deepen your knowledge, explore the different production stages and master all the essential techniques, find out how to work with Jesmonite in detail.
