Zverev's Triumph on Red Clay: The Invisible Process Engineering Behind Every Clay Court

23.06.2026, Remscheid, Germany

Sigurd Schütz, RHEWUM GmbH

What looks like sand at Roland Garros is actually ground brick - and its quality is decided not on the court, but in the screen mesh.

On 7 June 2026, Alexander Zverev fell backwards onto the red clay of Roland Garros, his hands clasped over his face. With a five-set victory over Flavio Cobolli, he won his first Grand Slam title - the first German to do so since Boris Becker in 1996. The day before, on the women's side, 19-year-old Mirra Andreeva had triumphed.Amid all the drama, one image stays with us: the controlled slide into the forehand, the fine red dust cloud over the baseline, the unmistakable smell of watered ash. Anyone who has ever played on „clay" knows it. Except: it isn't clay at all. The character of this surface is determined long before the first ball is struck - in a production process involving crushers, conveyor belts and precise screening machines.

Not Beach Sand, but Fired Clay

What crunches underfoot is ground brick. Tennis clay, also known as brick dust or tennis sand, is made from single-source crushed fired clay bricks - roof tiles, clinker, wall bricks, often defective batches straight from the brick industry. Binders such as lime or cement are deliberately left out; the red surface holds together purely through the right grain composition. High-quality clay blends different firing hardnesses: hard roof-tile fragments for wear resistance, a share of softer wall brick for binding and the vivid red colour. German clubs alone wear through around 100,000 tonnes of tennis clay per year.

From Lump to Grain

The journey begins coarse: a wheel loader moves the crushed material into the feed hopper and on into the crusher, which breaks down the material. But crushing alone does not make a playable court. What comes out of the crusher is a wild mix of all grain sizes. Only classification - separating by grain size - turns the bulk material into a defined product. And this is exactly where it is decided whether a court is playable.

Why Grain Size Decides Everything

Tennis clay is produced according to DIN 18035-5, with quality assurance per RAL-GZ 515/1; common final grain sizes are 0/2 and 0/3 mm (approx. 0 to 0.08 in. / down to no. 10 mesh, and 0 to 0.12 in. / down to no. 7 mesh). The standard, however, requires not just one grain size but an entire grain-size distribution within tight tolerances. Simplified: the ultra-fine fraction below 0.06 mm (approx. 0.0024 in. / no. 230 mesh) stays limited, the medium fine-grain range from 0.06 to 0.70 mm (approx. 0.0024 to 0.028 in. / no. 230 to no. 25 mesh) dominates the tennis clay at around 40 percent, and the coarser grain remains in the minority.

The grain distribution directly determines water permeability, frost resistance, wear resistance and shear strength. Too much ultra-fine grain: the court becomes dense and unstable. Too much coarse grain: appearance and shear strength suffer. The player's clean slide, the consistent bounce behaviour, the puddle that seeps away within minutes after rain - all of this is the result of a sharp separation through screen meshes of just a few tenths of a millimetre in aperture.

The Fine Art of Fine Screening

Brick dust is a demanding feed material: naturally moist and hygroscopic, in other words actually sticky. Moisture combines with dust and fine particles to form agglomerates that cling to the screen mesh and blind it if the machine has no effective self-cleaning system. Trapped grains block the fine meshes, the separation cut shifts, and the product falls outside the standard. Rule of thumb for practitioners: The wetter the raw material and the climate, the faster the screening machines blind - and the finest screen decks fastest of all. In the coarse range, robust, simple vibrating screens suffice: two external unbalance motors set the entire machine into a linear oscillation and carry out the coarse separation. But the finer the separation cut, the less it helps to simply shake the housing. The decisive acceleration must reach where the separation happens: directly into the screen mesh.This is exactly what direct screen-mesh excitation achieves. External magnetic vibrators transmit a high-frequency oscillation directly onto the screen mesh while the housing remains static; accelerations of up to 50 g occur at the mesh, and automatic, regular cleaning impulses free it from trapped grains. The mesh keeps itself clear during operation - the separation cut stays precise for weeks.In the RHEWUM RHEsono^® series, this is implemented consistently; it separates precisely exactly where the quality of the tennis clay is decided. Where space is limited, the RHEsonox^® combines both worlds - linear oscillation and mesh excitation - in a low overall height and separates from around 50 µm to 6 mm (approx. 0.002 to 0.24 in. / no. 270 mesh to no. 3.5 mesh). Because only the mesh oscillates, the moving mass, energy consumption and dynamic loads stay low, and the static housing can be made dust-tight and connected to a dust extraction system - a matter of occupational safety with respirable brick dust.

THE SCIENCE OF SCREENING

And here lies the real point. Before screening, the material is little more than broken brick, often a worthless defective batch. After screening, it is a standardised, high-quality building material that determines the playing properties on thousands of courts. This transformation is achieved by separation - screening is the value-adding process step.Hardly anyone knows RHEWUM. Yet what our machines screen is everywhere: in the plaster on the wall, in the fertiliser on the field, in the sugar on the dinner table - and also in the red clay beneath the feet of tennis players. We don't stand in the spotlight. But we are successful. Because we make our customers successful.

The perfect clay court does not begin at the tennis facility. It begins in the screen mesh.