Shower tray slip ratings explained: what the numbers really mean

The label nobody reads (but should)

When buying a shower tray, most decisions revolve around three things: size, colour and price. The slip rating, if it even gets a glance, is dismissed with a quick “it says non-slip, that’ll do.” But that label contains technical information that can make the difference between a safe shower and a fall with serious consequences.

At Bathscape we take this seriously, because the data warrants it: according to the Spanish National Statistics Institute (INE), bathroom falls cause more than 70,000 emergency admissions per year in Spain. A significant proportion of those falls occur in the shower, on wet surfaces the user assumed were “non-slip.”

The issue is not that manufacturers lie. The problem is that the term “non-slip” without a class or coefficient means nothing concrete. It is like saying a car is “fast” without quoting a single speed figure.

The standards: DIN 51097 and the CTE

Two regulatory frameworks govern slip resistance on wet surfaces for barefoot use (such as a shower tray):

DIN 51097 — Classification A, B, C

This is the German standard (adopted internationally as a reference) that classifies surfaces into three classes based on the angle of inclination at which a barefoot user loses balance on a wet surface:

Class	Minimum angle	Safety level	Where required
A	≥12°	Basic	Dry changing rooms, pool deck corridors away from the basin
B	≥18°	Medium	Public showers, pool edges, wet stairs
C	≥24°	High	Sloping pool edges, inclined shower trays, ramps

The test is performed with real people walking barefoot on the inclined surface, wetted with water and a standardised surfactant. As the incline increases, there is a point at which the foot slips. The angle at which this occurs determines the class.

Class A is the minimum, and frankly, it is insufficient for a shower tray. Class A lets you walk on a wet, flat surface without much trouble, but as soon as soap, shower gel or foam is on the floor, grip drops dramatically.

Class B is the standard class required by Spanish regulation for showers in public spaces. It is not legally mandatory for domestic use, but it is the minimum any serious professional should recommend.

Class C is the highest grip level. The surface is rough to the touch, very safe but also harder to clean (the roughness traps dirt). It is the class we recommend for households with elderly residents, small children or anyone with reduced mobility.

CTE DB-SUA — What Spanish law actually says

Spain’s Technical Building Code, in its Basic Document on Safety of Use and Accessibility (CTE DB-SUA), establishes slip-resistance requirements for floors based on their location and conditions of use.

The CTE classification does not use letters (A, B, C) but numerical classes based on the slip-resistance value (Rd):

CTE class	Rd (slip resistance)	Application
Class 0	Rd < 15	Not suitable for wet areas
Class 1	15 ≤ Rd < 35	Dry interior with slope < 6%
Class 2	35 ≤ Rd < 45	Dry interior with slope ≥ 6%, stairs
Class 3	Rd ≥ 45	Wet areas (showers, pools, exteriors)

For a shower tray in a residential setting, the CTE requires class 3 (Rd ≥ 45). This is law, not a recommendation. Any shower tray installed in a new build or in a renovation that requires a planning permit must meet this requirement.

Coefficient of friction (CoF): the real metric

Beyond classes and regulations, the most precise technical indicator is the dynamic coefficient of friction (also called DCOF or μ). It is measured with a tribometer following a standardised procedure (ANSI A326.3 or UNE-ENV 12633).

CoF	Level	Interpretation
< 0.30	Dangerous	High slip risk. Unacceptable for any wet zone
0.30–0.45	Insufficient	Not suitable for barefoot wet use
0.45–0.60	Acceptable	Roughly equivalent to DIN class B
> 0.60	Good	Equivalent to DIN class C. Recommended for shower trays
> 0.80	Excellent	Maximum grip. Very rough surface

When a manufacturer says “non-slip tray” without quoting a class or CoF, be sceptical. A tray with a CoF of 0.35 technically has some slip resistance, but it is not safe for shower use.

Materials and their typical ratings

Not all materials behave the same. Here is what we have found in technical data sheets and through our direct experience with installations in Valencia:

Resin (Stonex, Solidstone, mineral-loaded)

The most widely used material in current shower trays. Its surface texture can be controlled during manufacturing, and most mid-to-high-range resin trays achieve DIN class C / CTE class 3 straight from the factory.

Brands such as Roca (with their Terran range) offer certified class C. The surface has a slightly granular feel that is not uncomfortable underfoot yet provides excellent grip, even with soap.

Advantage: class C without sacrificing comfort or aesthetics. Limitation: some budget-range resin trays (plain white, smooth finish) only achieve class A or B. Always check the technical data sheet.

Ceramic / porcelain

Ceramic trays vary significantly depending on the surface finish. A smooth glazed ceramic tray may be class A (insufficient). A ceramic tray with a textured non-slip glaze can reach class B or even C.

The issue with ceramic is that the non-slip treatment is superficial (a glaze layer). Over time and with use, that layer can wear down and lose its properties. In resin trays, the texture is integral (through the body), so surface wear does not affect the rating.

Natural stone

Entirely dependent on the finish. A polished wet stone surface is an ice rink. A stone with a flamed or bush-hammered finish can comfortably achieve class C. If you choose natural stone for your shower floor (common in walk-in designs with no visible tray), make sure the technical data sheet specifies the class under wet conditions, not dry.

Acrylic

Acrylic is naturally slippery when wet. Budget acrylic trays rarely exceed class A. Some carry a surface non-slip treatment (micro-etching), but its durability is questionable: in our inspections we have seen acrylic trays that lost their grip within 2–3 years of use.

At Bathscape we do not install acrylic trays. Not out of snobbery, but because the medium-term performance data does not convince us.

How to verify the actual rating

Step by step, here is what to look for:

1. Request the technical data sheet from the supplier. Not the commercial brochure (the glossy leaflet), but the technical sheet with test data. It should include the test standard (DIN 51097, UNE-ENV 12633 or equivalent), the class obtained and, ideally, the CoF value.

2. Look for the test certificate. Reputable manufacturers have tests conducted by accredited laboratories. In Spain, ASCER (Spanish Association of Tile and Floor Manufacturers) is the reference for ceramic materials, and the ITC (Institute of Ceramic Technology) in Castellón performs the tests.

3. Be wary of “non-slip” on its own. If the data sheet says “non-slip surface” without a class or coefficient, ask for clarification. If they cannot provide it, choose a different product. It is that simple.

4. Check whether the measurement is dry or wet. Some manufacturers provide slip-resistance data under dry conditions, which are irrelevant for a shower tray. The measurement that matters is always wet, barefoot.

5. Verify the reference standard. DIN 51097 (barefoot, wet) is the relevant standard for shower trays. DIN 51130 (with footwear) is for industrial floors and does not apply here, although some manufacturers cite it to make a class look better.

The roughness vs cleaning trade-off

Here comes the question we get asked at every renovation: “If the safest tray is the roughest, won’t it get dirtier?”

Yes. It is a genuine trade-off. A class C surface has micro-roughness that retains more limescale, soap and dirt than a smooth class A surface. But it is not an unsolvable problem:

• Hydrophobic treatments: surface hydrophobic treatments partially fill the micro-roughness without affecting barefoot grip. They reduce dirt adhesion and make cleaning easier.

• Regular cleaning: a class C tray cleaned weekly with a neutral product requires no more effort than a class A tray. The problem only arises when limescale is left to accumulate for weeks.

• Valencia’s water: given the hardness levels here (locals in every neighbourhood, from Benimaclet to Patraix, will tell you the same), limescale builds up faster. An anti-limescale product applied every 7–10 days keeps the tray spotless.

Our position: we prefer a tray that takes one extra minute to clean but prevents a fall. The hospital is farther away than the cleaning-products shelf.

Which class to choose based on your situation

Situation	Minimum recommended class
Adult with no mobility issues	Class B (minimum)
Family with small children	Class C
Elderly residents or reduced mobility	Class C
Trayless shower (floor-level wet room)	Class C
Occasional-use guest bathroom	Class B

For open shower designs such as a compact wet room, class C is essential because water spreads beyond the shower zone and the entire floor surface must be safe.

Frequently asked questions

Does the slip rating deteriorate over time?

It depends on the material. In resin trays with integral texture, the rating is maintained throughout the product’s service life. In ceramic trays with a superficial non-slip glaze, it can degrade with intensive use and aggressive cleaning products (neat bleach, industrial degreasers).

Can I improve the grip of a tray I already have installed?

Yes, but with limitations. Chemical treatments exist that are applied to the surface and increase the CoF (such as Antigliss or SafeStep systems). They work, but they require periodic reapplication. For a permanent solution, the option is to replace the tray with one that has factory class C.

Does the CTE mandate class 3 for residential renovations?

Technically, the CTE applies to new builds and renovations that require a permit. If you change the shower tray without altering structure or layout, many local councils do not require a full permit (only a prior notification) and the CTE does not strictly apply. However, our recommendation is to comply with it regardless of the legal obligation. It is not a bureaucratic issue — it is a safety issue.

What is the difference between a class C tray and adhesive non-slip strips?

Adhesive strips (with a rough surface) are a temporary patch. They peel off in heat and humidity, accumulate dirt at the edges and create an obvious aesthetic problem. A factory class C tray requires no add-ons: the safety is built into the material.

What really matters

The slip rating is not a dry technical data point for specialists. It is practical information that affects your daily safety. A shower tray is used 365 days a year, wet, with soap, sometimes in a hurry and sometimes half asleep. Perfect conditions for a slip.

Choosing class C does not cost significantly more than class A or B. The price difference between a class B and a class C resin tray from the same manufacturer is typically 30–80 €. Thirty euros for grip that could prevent a hip fracture.

At Bathscape, all our shower trays are class C DIN / class 3 CTE as a minimum. We do not offer a lower option because, frankly, we cannot find a reason to.

Explore tray options in our configurator and compare ratings before you decide. If you already have the design clear, check our complete shower tray comparison where we analyse materials, formats and prices in greater detail.