Jesmonite® Terrazzo Effect: How-To Guide for Makers

What is a Jesmonite® terrazzo effect?

Terrazzo is a speckled surface built from small chips set into a contrasting base. Traditionally it used marble or stone fragments in cement for floors and worktops. In decorative casting you recreate the same idea at a smaller scale for coasters, trays and dishes.

The key thing to understand is that real terrazzo chips are something you make yourself from Jesmonite®. You cast a thin sheet, let it dry, and break it into small pieces. Those handmade chips are what give a genuine Jesmonite® terrazzo its character, and making a few colours means every piece comes out unique.

Jesmonite® AC100 is the usual choice for indoor decorative terrazzo. It’s a water-based variant made for interior casting, it takes pigment easily, and it sands beautifully. Because it’s water-based, you don’t need gloves to work with it, which makes it a forgiving place to start.

What you’ll need

Gather everything before you mix. AC100 gives you a comfortable working window of about 10 to 15 minutes (a little less if the room is above 25 °C), so it helps to have your tools ready, there’s no need to rush, but a tidy bench keeps things relaxed:

• Jesmonite® AC100 Jesmonite® base and Jesmonite® liquid, both for your chips and for the base cast.
• Liquid pigments if you want coloured chips or a coloured base.
• A silicone mat, plastic sheet or a sheet of paper to cast your chips on.
• A silicone mould, browse the silicone moulds range, or the coaster and tray moulds to start.
• Mixing cups, a spatula or stirring stick, and a digital scale.
• P150 sandpaper and a sanding block for finishing.
• An acrylic sealer to finish the surface once it’s fully cured.

A digital scale matters more than you’d think. Jesmonite® is mixed by weight, not by eye, so accurate measuring is the difference between a solid cast and a crumbly one. The mix ratio for AC100 is 1:2.5 (Jesmonite® liquid to base) by weight.

1Make your terrazzo chips

The chips give terrazzo its character, and they’re easy to make in advance. Here’s how:

1. Mix a small amount of Jesmonite® AC100 at 1:2.5 (Jesmonite® liquid to base) by weight. If you want coloured chips, stir in a little liquid pigment, up to about 2% of the total mix weight is plenty.
2. Spread the mix in a thin layer on a silicone mat, plastic sheet or piece of paper.
3. Let the sheet dry for about 20 to 30 minutes, until firm.
4. Break the sheet into small chips. Aim for a mix of sizes, from fine grit up to flecks a few millimetres across, varied chips look far more natural than uniform ones.

Make several colours if you like, casting one thin sheet per colour. Keep your chips in small pots so you can grab a handful the moment your base is mixed. If you want ideas on which shades to combine, our colour guide is a good place to start.

2Cast the terrazzo

Now for the main event. Work steadily, AC100 gives you time, so there’s no need to panic:

1. Prepare your silicone mould on a level surface with your chips within arm’s reach.
2. Weigh out fresh Jesmonite® AC100 at 1:2.5 (Jesmonite® liquid to base). Not sure how much to make? Our mould product descriptions list the amount you need, or use an online Jesmonite® calculator or the Jesmonite® app.
3. Add the Jesmonite® base to the Jesmonite® liquid and stir until smooth and lump-free, with the consistency of pouring cream. For a coloured base, add a little liquid pigment now and stir it through.
4. Fold a portion of your chips into the mix so they sit suspended through the body of the cast.
5. Pour into your mould, then gently tap or vibrate it on the table to release air bubbles.
6. Leave the piece to set. AC100 can be demoulded after about 30 minutes and is fully cured after 24 hours.

Because the chips are folded right through the mix, the terrazzo pattern shows no matter how far you sand back.

3Sand while soft, then seal

This is the step that transforms your piece, and timing matters.

Sand as soon as you demould, while the cast is still relatively soft and easy to work. Grinding back the top layer slices through the buried chips and exposes their cross-sections as crisp, colourful specks. Wrap your P150 sandpaper around a sanding block, wet it with a little water to keep the dust down, and work the surface in steady circular motions until the pattern is clear and even. For a near-polished feel, follow up with finer wet-and-dry grits.

Seal once the piece is fully cured, after 24 hours. Bare Jesmonite® is porous, so an acrylic sealer in satin or gloss is the right finish for AC100. Sealing brings the colours back out, sharpens the contrast between chips and base, and gives a smooth, professional, wipe-clean surface. Apply thin, even coats and let each one dry before the next, thin coats always beat one thick coat, which can go patchy.

Jesmonite® casts are rigid and hard-wearing once cured, so a well-sealed terrazzo coaster or tray will stand up to everyday use.

A more natural-looking alternative: StoneRoxx and GlassRoxx

If you’d rather skip the chip-making step, there are two ready-made granulates that fold into a fresh Jesmonite® mix in exactly the same way. They give a terrazzo-like look with slightly more natural texture, though strictly speaking they aren’t terrazzo themselves.

StoneRoxx is real granite pieces. Being natural stone, they catch the light differently from the base and add genuine depth and texture.

GlassRoxx is a granulate made entirely from recycled glass, coloured with water-based pigments, so it brings colour and a subtle sparkle to a sustainable studio.

To use either, simply fold them into your mixed AC100 before pouring, then sand and seal as above. They’re a lovely alternative when you want the effect without making chips, but for a true Jesmonite® terrazzo, handmade chips are the way to go.

Terrazzo rewards experimenting. Cast a few thin sheets in different colours whenever you have Jesmonite® left over, and you’ll always have chips ready for your next piece.

Ready to start? Explore Jesmonite® AC100, liquid pigments and silicone moulds, and you’ll have everything you need to make your first terrazzo piece this weekend.