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What is a good water absorption figure for terrazzo?

It depends which grade you are buying, because the Chinese standard grades it: 8.0% or less for standard terrazzo, 6.0% for high-performance, 4.0% for cement artificial stone, and 1.0% for the high-performance version of that. Absorption is the figure that decides whether you seal, and how often.
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 Water absorption What that means for the floor
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

Why the processes are not interchangeable

Cement-bound terrazzo absorbs through the matrix, so the number tracks the ratio of cement to stone rather than the hardness of the chips. An 8% floor takes oil and colour into the matrix within months; a 1% floor behaves much more like a tile. The test that produces the figure is straightforward and worth understanding because of how it is reported: specimens are dried at 105 plus or minus 5 degrees Celsius to constant mass, then immersed with the water standing 50 plus or minus 10 millimetres above the top face for 24 hours. JC/T 507-2022 takes the single WORST result in the group, not the average.

What these figures are, and what they are not

The four grades are from JC/T 507-2022 table 7; the procedure is clause 7.5.3 of the same standard. The single-worst-specimen reporting is stated in that clause and is the detail most often argued about between suppliers. ⛔ These are published requirements. We have not tested a panel we supplied.

Measured data sheets and test reports

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