How many times does a terrazzo floor get ground?

At least three passes on a standard cement-bound floor, and on a high-performance floor the count is set by design rather than by a rule. The pass count is in the code; the grit sequence is in practice, and it steps up in stages: a coarse cut to expose the aggregate, a transition pass, a grout coat, then progressive refinement.

The six processes drawn to one scale. Layer thicknesses are published ranges.

The figures, and where each one comes from

Stage	Diamond grit	What it does
Rough cut	16 to 40, metal bond	cut back to the top of the divider strips
Transition	80 to 120	remove the heavy scratches from the rough cut
Grout coat	epoxy slurry	fill the pinholes the rough cut exposed
Standard finish	120, then 220 and 400	the finish level the trade recognises
High polish	800, 1500, 3000	from 800 grit no topical sealer is required
Total passes, standard floor	not fewer than 3, GB 50209-2010 cl.5.4.5
Flatness checked with	3 mm standard, 2 mm high-performance

Why the processes are not interchangeable

Grinding is not a finishing step; it is how the floor is made. The aggregate is graded through the matrix, so the surface does not exist until a grinder has cut through the cement to the stone, and because the chips are at different depths a single pass would leave high stone and low cement at once. That is why each stage uses a finer grit and takes less off, and why 120 grit is the level the industry treats as the standard finish — it is the last stage that still needs a sealer over it. The flatness that results is checked against 3 millimetres on a standard floor with a straightedge, and the same 3 millimetre allowance appears in the North American system expressed over a six-foot straightedge, which is close enough to the two-metre one to be the same number said in different units.

What these figures are, and what they are not

The three-pass minimum and the 3 and 2 millimetre flatness allowances are GB 50209-2010 clause 5.4.5 and table 5.1.7. The grit sequence and the 120-grit standard finish level come from published terrazzo specifications that state they follow the NTMA epoxy guide, and from trade accounts of the same sequence; ⛔ they are practice rather than a clause, and the codes we have read set only the pass count and not the grit numbers. ⛔ We do not install floors and hold no grinding records for any floor we supplied.

Measured data sheets and test reports

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