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Answers

How thick should a terrazzo floor tile be?

Twelve to eighteen millimetres for an installed terrazzo topping, and the code does not leave it as a preference: JC/T 507-2022 limits the largest stone chip to two thirds of the topping thickness. Twelve millimetres of topping therefore caps the chip at eight, and eighteen millimetres allows twelve.
Chip size against topping thicknessA horizontal scale in millimetres. For each topping thickness from 8 to 18 millimetres, a bar shows the topping and a second bar shows the largest stone chip permitted, which is two thirds of the thickness. Derived from JC/T 507-2022 clause 5.3.0481216208 mm5.3 mmthe band we supply10 mm6.7 mm12 mm8 mm15 mm10 mm18 mm12 mmTopping thickness (solid) against the largest chip permitted (accent), on one millimetre scale.Chip ceiling is two thirds of the thickness (JC/T 507-2022 cl.5.3).Topping range from GB 50209-2010 cl.5.4.1; the arithmetic is ours.
Chip size against topping thickness, on one millimetre scale. The chip ceiling is two thirds of the thickness, from JC/T 507-2022 clause 5.3; the arithmetic on the thicknesses is ours.

The figures, and where each one comes from

Topping thickness Largest chip permitted Chip that reads at that limit
12 mm 8 mm medium aggregate
15 mm 10 mm medium to large
18 mm 12 mm large aggregate
20 mm precast panel not applicable, the body is through-thickness whole-body aggregate

Why the processes are not interchangeable

This is the constraint that separates a specification that will work from one that will crack. Aggregate near the surface is what carries wear, but a chip that is too large for the thickness it sits in is no longer reinforcement, it is a void with a hard edge in it, and the grinding pass that exposes it leaves a pocket. It also explains a difference between systems that otherwise look interchangeable: a 20 millimetre precast panel is solid all the way through, so its aggregate is through-thickness and the two-thirds rule does not apply to it. The rule constrains a topping laid on a substrate, where the back of the topping is a flat plane rather than more stone.

What these figures are, and what they are not

The 12 to 18 millimetre range is GB 50209-2010 clause 5.4.1, which states that it should follow the chip size. The two-thirds relationship is JC/T 507-2022 clause 5.3. The millimetre chip figures in the table are our arithmetic from those two clauses, not quoted figures. ⛔ These are published requirements. We have not measured a panel we supplied.

Measured data sheets and test reports

If you are specifying this

These are the forms we actually supply for this question, with production photographs where we have them:

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