Surface Roughness (Rz) Testing

What is surface roughness (Rz) testing?

Surface roughness testing measures the micro-texture of a floor surface in microns, using a calibrated stylus-based profilometer. The output most relevant to slip resistance is the Rz value — the average peak-to-valley height across the measured trace.

Rz testing is complementary to pendulum testing rather than a replacement for it. Where pendulum testing measures the floor's actual slip-resistance performance, Rz testing measures the underlying surface property that drives wet-state performance. The combination gives a much fuller picture of why a floor performs the way it does — and how to fix it if it's failing.

Why does roughness matter?

When a floor is wet, the only thing that prevents a foot or shoe from skating across the water film is the texture of the surface itself — the peaks of micro-roughness penetrate the water and create real friction. The UK Slip Resistance Group's published guidance gives recommended minimum Rz values for different floor types and contamination scenarios:

• Rz ≥ 10 microns — for water-only contamination on most surfaces;
• Rz ≥ 20 microns — for soapy water (changing rooms, swimming pool surrounds);
• Rz ≥ 35–40 microns — for fat / oil contamination (commercial kitchens, food service);
• Rz ≥ 45+ microns — for heavy contamination scenarios (industrial process floors).

When do we recommend Rz testing?

We recommend including Rz testing alongside pendulum testing whenever:

• A floor's wet-state PTV is borderline (low end of the moderate band);
• You're investigating an apparently compliant floor that has a history of slip incidents;
• You're specifying a new floor and want to verify that the manufacturer's published roughness will be retained over time;
• You're testing a floor before and after a cleaning, sealing or coating intervention;
• You're preparing forensic evidence in support of a slip claim and need to identify whether the surface was inadequately textured at the material time.

What's included in the Rz report?

Rz testing is delivered as either a standalone report or as an addendum to a pendulum test report, depending on what the client requires. The Rz report includes the calibration record of the profilometer, the trace length and direction at each test point, and a tabulated Rz value with comparison against UKSRG-recommended minima.

Book this service in Nottingham or the East Midlands

To request a quote for surface roughness (rz) testing at a specific site, call us on 0208 246 5562, email info@surfaceperformance.com, or use the enquiry form. We typically issue fixed-price quotes within the same working day.