How wide should the joints between terrazzo tiles be?

As narrow as the tiles allow — NTMA names one-sixteenth or one-eighth inch as the standard divider widths, and a wider joint interrupts the aggregate pattern and starts to read as a porcelain floor rather than a terrazzo one. Use a grout matched to the matrix, not a generic one.

Reference photograph of a terrazzo surface, s08. Not a photograph of our goods. — Four grey and black tiles laid flat, one dark one pale

Reference photographs. They show the material and the finish; they are not photographs of goods we made, and the colour on screen is not a colour-match.

The figures, and where each one comes from

Joint	What it does to the look
1/16 in	almost invisible, needs precision
1/8 in	the stated standard, a shadow line
1/4 in	visible, reads as tile rather than as terrazzo
18 to 24 gauge	the same widths expressed as strip gauge, per NTMA

Why the processes are not interchangeable

A terrazzo tile gets its character from the aggregate running edge to edge, and a joint wider than about an eighth of an inch interrupts that at every edge of the room. This is also why grout colour is chosen against the matrix rather than against the chips: the grout is a line in the pattern, and if it is lighter than the matrix it becomes a grid that draws attention away from the floor. NTMA treats the divider strip as both a technical and a design element for the same reason, and notes that where major movement is expected the answer is an inset expansion plate rather than a wider joint.

What these figures are, and what they are not

The one-eighth and one-sixteenth inch widths, and the 18-to-24-gauge strip range, are from the NTMA Terrazzo Systems Reference Guide. ⛔ GB 50209-2010 sets no figure for divider strip spacing or width, so ⛔ there is no Chinese equivalent quoted here and none should be inferred from the absence.

Measured data sheets and test reports

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