How to Make Jesmonite® Coasters (Step-by-Step Guide)

Not sure how much to mix? Use our free Jesmonite® calculator — enter the water weight of your mould and it gives you the exact liquid and base amounts.

This guide walks you through the whole process from empty mould to a sealed, drink-ready coaster. Follow the steps in order and you will end up with a smooth, durable set that shrugs off wet glasses.

What you’ll need

You do not need a full workshop. Here is the short shopping list for a set of coasters:

• The material: AC100 is the go-to for indoor decorative casting. It is water-based, non-toxic and beginner-friendly, which makes it ideal for homeware like coasters.
• A coaster mould: browse the coaster & tray moulds for round, square and geometric shapes.
• Colour: a few liquid pigments, a little goes a long way. We also stock powder neon pigments if you want brighter, punchier shades.
• A sealer: an acrylic sealer, available in satin or gloss, to make the surface water-resistant (more on this below).
• Basic kit: accurate digital scales, mixing cups, stirring sticks or a mixer, and P150 sandpaper with a sanding block for tidying edges.

If you would rather not source everything separately, an AC100 starter kit bundles the Jesmonite® base, Jesmonite® liquid and essentials so you can start straight away.

Preparing your mould and mix

Good preparation is what separates a crisp coaster from a bubbly, chalky one. Take a few minutes here before you mix anything.

Work out how much you need. With AC100, measure the amount of water it takes to fill your empty mould, then add about 10% as spare (some mix always stays behind in the cup). Divide that figure by 2 to get your Jesmonite® liquid amount, then multiply the Jesmonite® liquid by 2.5 to get your Jesmonite® base powder. Repeat for the number of coasters you are casting. For a full walkthrough, see our guide on how much Jesmonite® you need.

Check the ratio. AC100 mixes at 1:2.5 by weight, meaning 1 part Jesmonite® liquid to 2.5 parts base powder. The calculation above already gives you both figures; if you want to sense-check quantities, most of our own mould product descriptions list the amount you need, or you can use an online Jesmonite® calculator or the Jesmonite® app.

Set up your space. Make sure the mould sits level so the coasters cure to an even thickness. Have your pigment, stirring stick and a toothpick within reach, because once the Jesmonite® liquid and powder meet you have a comfortable working window of about 10 to 15 minutes (a little less if the room is above 25 °C).

Step-by-step: casting your coasters

Here is the core method. Work steadily and do not rush the mixing stage.

1. Add the liquid first. Pour the measured Jesmonite® liquid into your mixing cup, then add pigment if you want colour and stir it into the liquid.
2. Add the powder. Tip in the Jesmonite® base powder and mix thoroughly until you have a smooth, lump-free, pourable consistency. A high-shear mixer on a drill gives the most even result, but a firm hand and a stick will do.
3. Pour into the mould. Pour slowly, in a thin stream from around 10 cm above the mould, until it is filled to the top.
4. Release the bubbles. Gently tap and vibrate the mould on the table so trapped air rises to the surface, then pop any stubborn surface bubbles with a toothpick. This tapping is the main way to get a bubble-free coaster. Only for moulds with a lot of fine detail, you can first brush a thin layer into the cavity, but for most pieces this isn’t needed. For larger pieces or very detailed moulds, a vibration plate makes releasing bubbles even easier.
5. Level and leave. Check the mould is still level, then leave it undisturbed to set.
6. Demould. AC100 is ready to demould after about 30 minutes. Leaving a cast in the mould too long can make it “sweat” and pick up marks.
7. Sand early, then cure. Sand as soon as possible after demoulding, while the cast is still relatively soft and easier to work. Then let the coasters cure fully for 24 hours before sealing. Jesmonite® keeps getting stronger as it cures over that first day.

Colour and terrazzo options

Plain coasters look great, but this is where you can have fun. A few ideas:

• Solid colour: stir a single pigment fully into the Jesmonite® liquid before adding powder for a clean, even tone. Jesmonite® is opaque, so pigments give you a rich solid colour.
• Marbled: mix two colours in separate cups and swirl them together in the mould without over-stirring.
• Neon accents: neon pigments work perfectly with AC100 (and can be used with AC84 too) if you want brighter, punchier coasters.
• Terrazzo: for that classic speckled look, make your own Jesmonite® chips and fold them into a fresh mix (see our terrazzo guide for the full method). For a quicker terrazzo-like effect, ready-made StoneRoxx granite pieces or recycled-glass GlassRoxx are slightly more natural alternatives that fold into the mix the same way and add texture and colour.

Keep pigment doses modest: you can add up to about 2% of the total mix weight in pigment, and beyond that it can affect how the cast sets. Because a little goes a long way, it is easy to add more but impossible to take it out.

Sanding and sealing for drink use

This step matters more for coasters than almost any other project, because they meet wet glasses, condensation and the occasional spill.

As soon as you have demoulded, sand the edges and back smooth while the cast is still relatively soft and easier to work. Use P150 sandpaper wrapped around a sanding block, working evenly around each edge. If a coaster has rougher spots, start coarser and finish with P150 for a clean feel.

Then seal. Jesmonite® is porous, so an unsealed coaster will absorb moisture and can stain or mark from a cold, wet glass. Apply an acrylic sealer made for AC100, available in satin and gloss, in thin coats, letting each coat dry. Sealing gives you a wipe-clean, water-resistant surface that stands up to daily use. For indoor coasters, an acrylic satin or gloss sealer is the right choice; a penetrating sealer is aimed at outdoor, cement-based casts instead. For the full method (including the handy 50/50-with-water trick), see our guide to sealing Jesmonite®.

Ready to cast your own set? Pick a shape from the coaster & tray moulds, pair it with AC100 and your favourite pigments, and you can have a finished, sealed set ready by the weekend.