Terrazzo is not a colour effect. It is an assembly: pieces of set material suspended in a second pour, then cut back until the pattern appears.
It takes two sessions, and the second one only works if the first was done properly.
Phase 01 · Make the chips
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Cast a flat slab in each colour you want
A shallow, flat mould is ideal. The slab exists only to be broken, so it does not need a good surface.
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Let the slabs cure fully
Chips broken from a piece that is not fully set will crumble at the edges rather than fracture cleanly, and soft chips will smear into the base mix.
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Break them, do not cut them
Wrap a slab in cloth and break it. Fractured edges catch light and read as terrazzo; cleanly cut squares read as tiles.
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Sort by size
Separate the sizes into rough grades. Mixing a controlled range gives a pattern you designed; using everything gives a pattern that happened to you.
Phase 02 · Cast the piece
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Decide chip density before you mix
More chips means a busier, more stone-like face. Fewer means a quieter surface with occasional incident. Start on the conservative side — it is easy to add more on the next piece and impossible to remove them from this one.
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Pour a thin base layer first
A shallow layer of plain mix in the bottom of the mould keeps chips from pressing hard against the mould face and showing as flat, cut-off shapes.
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Fold the chips into the remaining mix
Fold rather than stir. You are distributing solids, not aerating a mixture.
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Fill and settle
Pour, then tap the mould firmly. Chips make it harder for air to escape, so this needs more attention than a plain cast.
Phase 03 · Reveal it
This is the phase people underestimate. Until you sand, a terrazzo piece looks like a plain one.
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Wait until it is properly hard
Sanding a piece before it has strength drags chips out of the surface and leaves craters where the pattern should be.
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Cut back the top layer
Start coarse and work evenly across the whole face. The chips appear gradually as the surface layer comes away.
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Stop when the pattern is right
There is a moment where the density looks correct. Going further does not improve it — it just makes the piece thinner.
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Refine through finer grits
Once the pattern is revealed, work through the grades to bring the chips and the base to the same smooth plane.
Things worth knowing
- Contrast does the work
- Chips close in tone to the base disappear. The palette is deliberately soft, so pair the lightest base with the deepest chips you have if you want the pattern to read across a room.
- Chips are a good use of failed casts
- Every piece with a bubble or a chipped rim is a future slab. Nothing in this process is wasted.
- The base ratio still matters
- A base mix carrying solids benefits from being mixed to flow properly. See the mixing-ratio lesson before you commit a large piece.
Questions people ask
How many chips should I use?
There is no single correct proportion — it is a design decision, and it depends on chip size as much as quantity. Cast one small test tile at a density you think is right before committing to a large piece.
Can I skip the sanding?
No. Sanding is what makes it terrazzo. Without cutting the surface back, the chips stay buried under the outer layer of the base mix.
Can I use something other than FormCast+ for the chips?
Other inclusions can be set into a cast, but they behave differently — they can move, absorb water from the mix or refuse to bond at the edges. Chips made from the same material are predictable, which is why the technique starts there.
