Jesmonite is a material prized for its ease of use and the many creative possibilities it offers. Among the various Jesmonite products available, each is designed for specific uses, but all require a few adjustments and good practices to produce perfectly smooth, strong and flawless pieces.
Whilst creating your pieces, you may encounter air bubbles, find that your mixture sets faster than expected, or discover that your creation breaks when removed from the mould. These issues are among the most common challenges faced when starting out with Jesmonite®. Find out what causes these issues and discover our practical tips for avoiding them, so you can create your pieces with greater confidence.
In addition to these tips, don’t forget that Jesmonite offers plenty of scope for customisation. Thanks to pigments and various colouring techniques, you can create objects that perfectly match your style.
Bubble formation
Are you making, or about to make, your first Jesmonite creations, but have noticed that small bubbles have formed in your mixture when removing the piece from the mould? Don’t worry, we’ll give you some tips to prevent this from happening again, or at least minimise it.
Why air gets into your mixture
There are several reasons for this:
- Mixing too vigorously traps air without it being immediately visible.
- Mixing for too long. The longer you mix, the more opportunity there is for bubbles to form.
- Pouring the powder into the liquid too quickly, or moving the mould whilst doing so, traps air at various levels.
- Failing to ensure the material fills the corners and details right from the start allows pockets of air to become discreetly trapped.
As long as this air remains trapped, it won’t disappear: it eventually rises to the surface once the piece has set, leaving unsightly marks.
A few adjustments are all it takes to make a world of difference
Here are the habits to adopt to significantly improve the final result.
When mixing:
- Pour in the liquid first, then the powder.
This prevents dry lumps from forming, so you won’t need to stir for ages to get rid of them. - Mix gently, without any sudden movements.
A steady, controlled motion is enough to blend the mixture evenly without incorporating excess air. - Choose the right utensil for the quantity you’re making.
A spatula is recommended: it allows you to fold in the mixture gently, break up any lumps and remove air without over-stirring. Avoid using a whisk, as it tends to incorporate more air whilst mixing. - Scrape the sides and bottom of the bowl regularly.
This ensures a smooth mixture and prevents dry patches from forming, which would compromise the final texture.
When pouring:
- Pour in a thin stream, always in the same spot.
Allowing the mixture to flow naturally from a single point minimises turbulence and prevents air from becoming trapped in the mixture. - Start with a small amount at the bottom of the mould.
Allowing the mixture to reach the edges and detailed areas right from the start helps to displace air before it becomes a problem. Don’t hesitate to quickly apply a first layer to the bottom and sides of the mould.
Once the mould is full:
- Tap or gently vibrate the mould.
This causes any remaining air bubbles to rise to the surface and escape before the material begins to set. - Use a vibrating table.
Our Jesmonite® vibrating plate gently agitates the mould to help bubbles rise to the surface and escape. It is particularly useful for detailed pieces or when a flawless, professional finish is required.
My mix is setting too quickly
Rapid setting is a characteristic specific to Jesmonite. This material hardens quickly by nature: the best approach is therefore to work in small batches and proceed swiftly once the components have been mixed. Preparation must be immediate and the working time is short. Hence the importance of having everything to hand, mould, pigments and tools, before you even start mixing.
What causes it to set too quickly?
Several factors can speed up the curing process:
- A batch prepared in too large a quantity.
- A workpiece that is too warm.
- A preparation that drags on.
Reminder: the material begins to set as soon as mixing is complete. Every minute therefore counts in the process.
How to save time
Two simple habits can help you buy time:
- Plan everything in advance before mixing: tools, the mould and pigments must be ready beforehand.
- Only prepare the amount needed for the current pour; don’t over-prepare.
Good to know: Jesmonite offers setting retarders suitable for each system, to be used if your project requires more leeway.
The Jesmonite setting retarder: extend the working time
The setting retarder is an additive specially formulated to increase the working time of Jesmonite before it hardens. Available for Jesmonite AC100, AC84 and AC730, it gives you a few extra minutes to mix, colour and pour the material under better conditions, whilst offering greater ease and precision when creating your pieces.
We offer two setting retarders:
- The AC100-compatible retarder: extends the working time by 25 to 30 minutes.
- The retarder compatible with AC84 and AC730: extends the working time from 45 to 60 minutes.
My piece breaks when I remove it from the mould
Breakage when removing the piece from the mould is most often caused by removing it too early or by the piece being too fragile for the shape of the mould. We recommend that you wait until the piece has set sufficiently before removing it, whilst taking care not to leave it in the mould for too long.
Common causes
A thin piece, with protruding details or very delicate areas, is more likely to break when removed. A mixture that is incorrectly proportioned or not sufficiently homogeneous can also make the object more fragile.
How to minimise the risk
Wait until the piece has set sufficiently, then remove it from the mould using slow, steady movements, without applying force to the delicate parts. We advise preparing a clean, well-designed mould from the outset, as good preparation makes removal easier and reduces the impact on the piece.
In practice, the best strategy is to adhere to the recommended setting time, avoid handling the piece whilst it is still warm or pliable, and opt for less fragile shapes for your first creations.
Master Jesmonite with ease using these tips
Minor imperfections encountered during your first Jesmonite projects are perfectly normal and will quickly disappear with a little practice. By using the correct proportions, preparing your materials in advance and following the correct procedures when mixing, pouring and demoulding, you’ll produce cleaner, stronger creations with a professional finish. Each attempt will help you refine your technique and gain greater mastery.
To deepen your knowledge, discover the different stages of production and master all the essential techniques, find out how to work with Jesmonite in detail.
