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Answers

How is the chip mix chosen?

By the system first and the look second. The chip cannot exceed two thirds of the topping thickness, and within that the size is chosen for how the surface will behave: fine aggregate grinds flatter and holds a tighter surface, large aggregate reads as a statement and leaves deeper pockets. A mix is graded across sizes rather than single-sized.
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

Chip Effect on the surface Where it suits
Fine flat after grinding, tight, easy to keep clean kitchens, wet areas, thin systems
Medium the conventional look, pockets stay shallow general floors
Large reads as aggregate, deep pockets hold dirt feature floors, thick systems
Glass highest contrast, and brittle under a point load ⛔ not in a working kitchen

Why the processes are not interchangeable

Grading is what makes terrazzo a surface rather than a pattern. A single-sized chip lays flat and grinds unevenly, because the stones all present the same height to the grinder and the ones at the edge of a chip are levered out; a graded mix has stones of different sizes in the same depth, so as the grinder takes the surface down a new layer of stone is always coming up. That is also why the two-thirds rule matters beyond safety — it keeps the largest stone far enough below the face that the grinder reaches the matrix before it levers a chip out, and at 8 millimetres that ceiling is about 5.3.

What these figures are, and what they are not

The two-thirds relationship is JC/T 507-2022 clause 5.3 and the chip ceiling at each thickness is our arithmetic on it. The grading practice is NTMA's published customary use per system. ⛔ The advice about glass in a working kitchen is general: we have no impact test on any mix and no figure supports it.

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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