How Sintered Stone Is Made
Four production stages — granulation, vacuum pressing, sintering and finishing. What is checked at each one, and why the control routine matters more than any single measurement.
Manufacturing reproduces a process that takes nature millions of years: minerals turn into monolithic rock under pressure and heat. On the factory floor the same cycle takes hours — and that is precisely why it can be controlled.
Stage 1. Preparing the body
Natural minerals are ground into powder and blended in a fixed proportion. The powder is then granulated into particles of uniform size. Granulate uniformity directly determines the density uniformity of the future slab: an uneven fill produces uneven shrinkage during firing, and warping with it.
Stage 2. Vacuum pressing
The granulate is poured into a mould and pressed at roughly 25,000 tonnes. Vacuum removes air from the body before the pressure is applied — any trapped bubble would become a pore in the finished slab, and a pore is both water absorption and the starting point of failure.
Stage 3. Sintering
The pressed blank passes through a kiln several dozen metres long at 1170–1230 °C. Particles bond, part of the body converts into a glass phase and binds the crystalline phases into a monolith. No organic binder is added at this point — the material comes out uniform in composition all the way through.
Overfiring warps the slab; underfiring leaves micropores. This is why the quality of sintered stone depends so heavily on the plant: the equipment costs a fortune, and cheap alternatives from unnamed lines are almost always a gamble.
Stage 4. Finishing
After firing, the slab receives its surface. Matt is an even, glare-free finish with slip class R10–R11. Polished is a mirror polish that emphasises the pattern, R9. Soft is a semi-matt sheen, pleasant to the touch, R10–R11. Microtech is a relief that matches the printed pattern. Body colouring and inkjet printing happen at this same stage.
Batch control: three parameters every four hours
| Property | Tolerance | Test method |
|---|---|---|
| Colour | ΔE ≤ 0.3 | measured every 4 hours |
| Thickness | ±0.2 mm | measured every 4 hours |
| Water absorption | ≤ 0.1 % (actual ≈0.02 %) | EN ISO 10545-3 |
Colour, with a tolerance of ΔE ≤ 0.3. ΔE is a numerical measure of the difference between two colours in perceptual colour space: below 1 the difference is usually invisible to the eye, at 1–2 it becomes noticeable in direct side-by-side comparison, above 3 it is visible even from a distance. The production tolerance is three times stricter than the threshold of perception, and the practical consequence is simple: a year later you can order more material to extend the project and lay it directly against the existing surface.
Thickness, with a tolerance of ±0.2 mm. On small formats half a millimetre is barely visible. On a slab 3.2 m long it produces a noticeable step at the joint — especially on a polished surface, where light exaggerates any difference in level.
Water absorption, with a control threshold of 0.1 % against an actual value near 0.02 %. Measured to EN ISO 10545-3. The figure works as an indicator of the whole structure: if water absorption rises, open pores have appeared in the body of the slab, and frost resistance and stain resistance leave with them.
Why frequency matters more than precision
A single measurement characterises a sample. A measurement every four hours characterises the process: it catches drift — the gradual departure of a parameter that is invisible on one slab but turns a 2,000 m² batch into two visibly different halves of a project.
The control routine matters more than any individual measurement: it turns a specification from a property of the sample into a property of the batch.
Frequently asked questions
At what temperature is sintered stone fired?
The pressed blank passes through the kiln at 1170–1230 °C. Part of the body converts into a glass phase and binds the crystalline phases into a monolith. No organic binder is added at this stage.
Why is vacuum needed during pressing?
Vacuum removes air from the body before the pressure of around 25,000 tonnes is applied. Any trapped bubble would become a pore in the finished slab, and a pore is both water absorption and the starting point of failure.
What does a tolerance of ΔE ≤ 0.3 mean?
ΔE is a numerical measure of the difference between two colours. Below ΔE 1 the eye usually sees no difference, so the production tolerance is three times stricter than the threshold of perception. In practice: a year later you can order more material and lay it directly against the existing surface.
