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Answers

Does terrazzo need sealing, and how often?

A cement-bound terrazzo floor does, because a cement matrix absorbs by definition — the Chinese classes run from 8.0 per cent downward, and the higher the absorption the more often the sealer is refreshed. A resin-bound terrazzo does not need one in the same way: it absorbs very little, which is why it is the usual choice on walls.
The four Chinese grades of terrazzoFor each of four grades, a bar shows the maximum water absorption in per cent and a figure gives the minimum average flexural strength in megapascals. From JC/T 507-2022 table 7.12468Standard terrazzo8%min. avg. 5 MPaHigh-performance6%min. avg. 8 MPaCement artificial stone4%min. avg. 10 MPaHigh-performance cement artificial stone1%min. avg. 15 MPaFour grades, not four points on a line: each is a separate product class.Water absorption, maximum permitted. From JC/T 507-2022 table 7. Axis starts at 1% because that is the lowest grade; it is not a zero-based axis.
The four grades of JC/T 507-2022 table 7, showing the maximum water absorption of each. The axis starts at 1%, not zero, and says so.

The figures, and where each one comes from

Grade Absorption What sealing means
Standard terrazzo not more than 8.0% seal, and expect to renew the sealer
High-performance terrazzo not more than 6.0% seal, less often
Cement artificial stone not more than 4.0% seal optional in most interiors
High-performance cement artificial stone not more than 1.0% approaching a vitrified surface
Epoxy, resin-bound very low sealed is not the question

Why the processes are not interchangeable

Sealing on terrazzo is what makes wet cleaning possible, and the grade tells you how much of a membrane you need. At 8 per cent absorption the matrix takes oil and colour in within months and the sealer is what stands between the floor and the stain; at 1 per cent the surface behaves much more like a tile and sealing becomes optional in an interior. The detail that matters when two suppliers disagree about performance is how the absorption figure was obtained: JC/T 507-2022 takes the single worst specimen in the group, not the average, so a floor with one bad tile in ten and a floor tested the same way report different numbers from the same slab.

What these figures are, and what they are not

The four absorption grades are JC/T 507-2022 table 7 and the single-worst-specimen rule is clause 7.5.3 of that standard. ⛔ No interval is quoted for renewing a sealer: the frequency follows from the grade and from wear, and giving a number here would be a maintenance schedule for a floor we have not seen. ⛔ We have not tested a panel we supplied.

Measured data sheets and test reports

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