Air Bubbles: How to Minimise Air Bubbles in Jesmonite AC100

Air bubbles. They might feel like they’re the bane of your Jesmonite life, but fear not! There are certain tips and tricks you can use to help minimise them. We’ve detailed a couple of easy ways to do this below, so your finished piece remains silky smooth!


  • 1x good quality paint brush 
  • Your mixed Jesmonite AC100 mixture
  • 1x silicone mould


  1. Coat your paintbrush in your fully mixed Jesmonite AC100 mixture.
  2. Brush this across the base of your silicone mould and all around the sides, making sure it’s completely even and covered. You can coat the brush some more if needed.
  3. Finish by slowly pouring the rest of your mixture into the mould, using the ‘tapping and slapping’ method as you pour, which we’re going to go on to below.


  1. Pour a little of your mixed Jesmonite AC100 mixture into the mould then gently ‘tap’ the sides of your mould with your fingers. 
  2. Next lift the mould and gently ‘slap’ it down on your work surface from a height of around 3cm. Keep repeating this, adding a little more mixture each time. You might find – especially when using a flatter mould like a coaster mould –  that it gets harder to ‘slap’ it as you fill it to the top. That’s ok. Just continue to tap the sides until the mould is full. 


  1. Start by holding your cup of mixed Jesmonite at a height of about 10cm away from your mould.
  2. Pour your Jesmonite in a slow, thin stream into your mould from the 10cm height. This will give any tiny air bubbles the chance to pop on the way down.


  1. Remember that what you see on the top of your mould will form the underneath of your piece so you won’t really see it. But if staring at those air bubbles on top is causing you unease, you can pop them using a toothpick before the Jesmonite sets. 

Pro Tip: Try using Jesmonite’s Retarder to slow down the time it takes for your Jesmonite to set. You only need to add 0.01% to your fully mixed Jesmonite, and it will give you more time to work on getting rid of those air bubbles. It’ll also thin out your Jesmonite mixture, meaning less chance of air bubbles forming. 

Now you can enjoy your air bubble-free creations! Let us know how you get on with these tips and if you have any questions feel free to drop us a message on WhatsApp (below) and we’ll do what we can to help.