How to Make Terrazzo
Source: Grey Element Projects • Full tutorial: www.craftingstepbystep.com/crafts/how-to-make-terrazzo
- Difficulty
- Advanced
- Hands-on time
- About 3 hours
- Wait time
- 8 hours
- Cost
- About $30 to $60
- Makes
- 1 terrazzo slab
Tools
- Drill with mixing paddle
- Mixing bucket
- Concrete grinder or angle grinder
- Diamond cup wheel
- Wet polisher
- Diamond polishing pads 50 to 3000 grit
- Trowel
- Straight edge
- Splash guard
- Dust mask
- Safety glasses
- Work gloves
Materials
- White cement
- Marble sand 0-2 mm
- Decorative chippings
- Microsilica
- Plasticizer
- Water
- Coated chipboard
- Release agent
- Marble powder
Steps
1. Choose Your Cement, Sand and Aggregate
Three components decide how the finished slab looks. White cement for a white base.
Tip: Buy more aggregate than you think you need. Running out mid-mix means a visible colour break in the finished slab.
2. Mix the Base
Three parts sand to one part cement by weight. Add a little microsilica, which makes the concrete harder, more flowable and generally easier to work with.
3. Add the Plasticizer
Mix plasticizer with water first, then add it to the batch. It drops the surface tension in the mixing water, so the concrete turns fluid and compacts almost on its own.
4. Fold In the Aggregate
Tip the chippings in and mix them through. Coarse aggregate makes the batch noticeably harder to stir, which is normal.
Tip: Stop mixing once the chips are evenly spread. Over-mixing just wears you out and starts breaking the softer stones.
5. Build and Release-Coat the Formwork
Coated chipboard screwed together makes a good form. The coating gives a smooth face and survives contact with wet concrete.
6. Pour, Compact and Level
Pour the terrazzo mix in and compact it by hand as you go. Stop about a centimetre below the top edge.
Tip: The fine cap gets ground away later, so it does not affect the pattern. It only exists to give you a flat surface to grind.
7. Demold the Slab
Take the form apart and lift the slab out once it has set. The face does not need to be flawless.
8. Grind the Surface
A diamond cup wheel takes the cement skin off and exposes the stones. A dedicated concrete grinder with dust extraction is the comfortable option, but a cup disc on any angle grinder does the same job.
Tip: Wet the surface to check progress. Dry ground concrete hides the aggregate; water makes the pattern show as it will look polished.
9. Fill the Pinholes
Grinding opens up air pockets across the face. Left alone they stay as visible pits.
10. Wet-Polish to a Gloss
Polishing is the step that turns a flat grey slab into terrazzo. Use a wet polisher and work through diamond pads from about 50 grit up to 3000, roughly doubling the grit each pass.
Tip: Do not skip grits. Each pass removes the scratches left by the one before, and jumping ahead leaves marks that show up under the gloss.
