How flat is a terrazzo floor allowed to be?

Three millimetres on a standard terrazzo floor, two millimetres on a high-performance one, measured with a two-metre straightedge and a wedge gauge. That is GB 50209-2010, table 5.1.7. For comparison the same table allows five millimetres on a concrete slab and two on a self-levelling compound.

Reference photograph of a terrazzo surface, s06. Not a photograph of our goods. — Four pale panels laid flat, each a different mix

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

Surface	Flatness allowance	Measured with
Standard terrazzo floor	3 mm	2 m straightedge + wedge gauge
High-performance terrazzo floor	2 mm	2 m straightedge + wedge gauge
Concrete slab	5 mm	same
Cement mortar	4 mm	same
Self-levelling compound	2 mm	same

Why the processes are not interchangeable

The reason terrazzo gets a tighter number than concrete is that the topping and the slab are ground together into one surface. A dip that would be invisible under a concrete floor telegraphs through a ground terrazzo floor, because the grinding removes the high points and leaves the low ones. That is also why the substrate has to be flatter before the terrazzo goes down than a normal tile installation would demand: by the time the topping is finished, the tolerance of the finished floor is the substrate tolerance plus whatever the topping added.

What these figures are, and what they are not

Both figures are published allowances from GB 50209-2010 table 5.1.7, which applies to the installed floor. They are not a figure we have achieved on any particular job, and we do not publish measurements of our own finished floors.

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:

Send a specification Ask for a sample