Eco resin terrazzo is currently the most-requested technique in our DMs and at our Hyderabad workshops. And it makes sense: the look translates perfectly into small cast objects, the technique is repeatable, and a well-made terrazzo piece photographs in a way that punches far above its production cost.
I'm Anirudh, founder of Artriso. We developed CALSO ONE specifically for casting applications like this, and terrazzo has become one of the defining use cases. This guide covers the full process, from chip-making through to the sealer that makes the final surface read as a finished product rather than a craft project.
The CALSO ONE terrazzo palette
Terrazzo is an aggregated look: chips of one or more colours embedded in a contrasting base. Getting the palette right before you pour saves you from a muddy result.
The base is usually neutral. CALSO ONE Off White is the most common terrazzo base because it photographs as a clean, warm stone tone and makes coloured chips read clearly. CALSO ONE Brilliant White gives crisper contrast for designs where the chips are the visual focus. A charcoal or dark grey base, mixed with black oxide pigment, inverts the look entirely and works well for high-contrast terrazzo where the chips are pale or metallic.
The chips are where colour lives. Three combinations that work reliably in Indian studio aesthetics: Obsidian Black chips on an Off White base for the classic minimal look. Umber Brown plus Ember Red chips together on Brilliant White for a warm, earthy palette that suits Indian interiors. A split of Obsidian Black, a sky blue oxide, and gold mica chips on off white for a contemporary mixed palette that photographs well for gifting and retail.
The proportions matter. 15 to 20 percent chips by weight of the total cast mix is the working range. Below 15 percent the terrazzo effect reads as sparse. Above 25 percent the chips crowd each other and the sanding phase becomes difficult to control.
Phase 1: Making the chips
Good chips are what separate a terrazzo piece that reads as designed from one that reads as accidental. The process is the same as any CALSO ONE cast, but at a much smaller scale.
What you need. CALSO ONE powder, water, oxide pigments or mica powder for colour, a flat smooth surface (silicone baking mat or a laminate sheet works), and something to crush with: a hammer, a heavy rolling pin, or a palette knife for hand-crumbling.
The process. Mix small batches, 100 to 200 grams total, at the standard 3:1 ratio. Add pigment at a high concentration: for chips, you want a solid, saturated colour that will still read when set in a contrasting base. A pale pigmented chip will lose its presence in the final piece. Use a spatula to spread the mix into a flat slab 5 to 8 mm thick on your smooth surface. Aim for a consistent thickness across the slab.
Allow the slab to set for 45 minutes minimum before breaking. The slab will be firm to the touch but still slightly yielding internally. If you break it too early it will crumble unevenly. After 45 minutes, place the slab in a plastic bag and use a hammer to break it, or hand-break it into irregular pieces. Aim for a mix of sizes: fragments the size of a rice grain, fragments the size of a lentil, and occasional larger pieces up to about 10 mm. The variation in size is what makes terrazzo read as natural rather than mechanical.
Mix chip batches of different colours separately and store them in small containers. Once you have two or three chip colours ready, you can work on the cast.
Phase 2: Casting
What you need. CALSO ONE for the base mix (Off White or your chosen base colour), your prepared chips, silicone moulds, a digital scale, and a mixing bowl.
The process. Mix your base batch at 3:1 as normal. Add any base pigment before the chips. Once the slurry is smooth and uniform, fold in the chips. Use a silicone spatula and gentle folding strokes rather than vigorous mixing: you want the chips distributed evenly without settling to the bottom before you pour.
Pour the chip-loaded slurry into your mould steadily. Once poured, immediately tap the mould on your work surface five to ten times firmly. This releases air bubbles and encourages chips to migrate toward the mould surface, which is important because the visible face of most coasters and trays is the side that was facing down in the mould. Chips concentrated near that surface will reveal well in the sanding phase.
For trays and flat objects where the open face is the display face, you can also place a second layer of chips directly on top of the poured slurry and press them lightly below the surface before it sets. This gives maximum chip density at the display face.
Allow to set undisturbed. CALSO ONE demoulds in 45 to 60 minutes for coasters and thin pieces. Allow 60 to 90 minutes for trays. For the terrazzo technique, it is worth waiting the full 90 minutes for any piece over 8 mm depth before demoulding, as the sanding phase applies significant mechanical force to the surface.
Phase 3: Sanding and reveal
The sanding phase is where terrazzo becomes terrazzo. Before sanding, the top face of the piece looks like a plain cast with chips barely visible below a skin of base colour. After sanding, the chips are exposed at the surface and the characteristic terrazzo speckle appears. This is the most satisfying step in the process.
What you need. Wet/dry sandpaper: 120 grit and 320 grit minimum, 180 and 400 grit if you want a finer sequence. A spray bottle of water. A sanding block for flat pieces, or an orbital sander for larger trays. A dust mask: sanding eco resin produces fine mineral dust.
The process. Wet sand the display face starting with 120 grit. Spray water on the surface as you sand and keep it wet throughout. Work in circular motions across the whole face rather than concentrating on one area. As you sand, the base colour slurry comes away and the chip tops are exposed. Continue until chips are clearly visible across the whole surface and the high points of any chips are level with the surrounding base.
Switch to 320 grit wet sanding to remove the scratches from the first pass. The surface should feel smooth under your finger and the chip faces should have a clean, even sheen. If you want a very fine finish before sealing, a final pass with 400 grit gives an almost polished surface that responds particularly well to GlazeSeal.
Rinse the piece thoroughly to remove all sanding residue. Allow to dry fully before sealing. The dry piece will look slightly dusty and pale, which is normal. The sealer restores and deepens everything.
Finishing and sealing
Sealing a sanded terrazzo piece is where the work pays off. The sanded surface is micro-porous and absorbs sealer efficiently, which means the colour response is immediate and dramatic.
For high-gloss terrazzo where you want chips to read with clarity and depth, two coats of GlazeSeal applied with a soft brush is the standard finish. The first coat soaks in and raises the colour. The second coat forms the surface film. After two coats, the terrazzo surface has a ceramic-like quality: chips in distinct contrast against a deep, even base.
For a satin terrazzo that keeps the natural stone character without the sheen, Stone Wax is the right choice. Apply and buff with a soft cloth. Stone Wax deepens the colour more subtly than GlazeSeal and is particularly good for the earthy, minimal terrazzo palette where a high-gloss finish would read as too commercial.
For more detail on sealing protocol, coat counts by product type, and the difference between all three Artriso finishes, the sealing guide covers it in full.
The full CALSO ONE collection is the starting point for materials and moulds if you are setting up your first terrazzo production run.
Frequently asked questions
What ratio of chips to base mix should I use for terrazzo?
15 to 20 percent chips by total weight of the cast mix is the standard working range for CALSO ONE terrazzo. At this ratio, chips are distributed visibly throughout the piece without crowding each other or making sanding difficult. Below 15 percent the terrazzo effect reads as sparse. Above 25 percent the chips pack too densely and the base colour disappears. Start at 17 percent for your first cast and adjust from there.
How thick should terrazzo chips be for eco resin casting?
Chip slabs should be poured at 5 to 8 mm thickness. After curing and breaking, you want a mix of fragment sizes: small pieces roughly the size of a rice grain, medium pieces the size of a lentil, and occasional larger pieces up to 10 mm. The variation in chip size is what makes the terrazzo look natural rather than mechanical.
Can I skip the sanding step in eco resin terrazzo?
Yes, but the result looks different. Without sanding, chips sit below the surface and are visible through the base colour as a slightly textured layer. With sanding, chips are exposed at the surface and read as distinct, sharp-edged colour blocks against the base. Most studio terrazzo work uses the sanded and sealed finish because it reads as more intentional and photographs better for retail and gifting.
Does the sanding process weaken the eco resin piece?
No. Sanding removes only the surface layer of the cast and does not affect structural integrity. CALSO ONE reaches full mechanical strength at 24 hours. For the terrazzo technique, it is worth waiting the full 24 hours before beginning the sanding phase on any piece that will see functional use, even though the surface is firm enough to sand at 90 minutes.
Anirudh Rapole is the founder of Artriso, the Hyderabad studio behind CALSO ONE. Terrazzo questions? Email contact@artriso.com.
0 comments