A tile order rarely goes wrong because of colour. It goes wrong because of a specification sheet nobody reads closely enough.
Every glazed vitrified tile ships with a set of numbers on its data sheet: water absorption percentage, PEI rating, slip class, modulus of rupture. Most project teams glance past these and go straight to finish and size. That's understandable; the numbers look like fine print. But they're the part of the specification that decides whether a tile survives its actual job, not just how it looks in a sample box.
This is a short, practical guide to what those numbers mean and how to write them into a BOQ (Bill of Quantities) so the spec holds up when a contractor, a client, or a site inspector questions it. We put it together because project teams ask us for exactly this breakdown more often than almost anything else on a Grifine data sheet.
Four numbers decide whether a tile belongs on your project.
A glazed vitrified tile specification sheet usually carries four figures that matter more than anything else on the page: water absorption, PEI rating, slip resistance, and modulus of rupture. Each one answers a different question. Water absorption tells you where the tile can be used. PEI tells you how much foot traffic it will take before the glaze starts to show wear. Slip rating tells you how it performs once water gets involved. Modulus of rupture tells you how much load the tile body can carry before it breaks.
None of these numbers works in isolation. A tile with a strong PEI rating and the wrong slip class is still the wrong tile for a wet area. Reading a spec sheet properly means checking all four against the room, not picking the one that sounds most impressive.
Water absorption tells you where a tile can go
Under the ISO 13006 / EN 14411 classification, tiles are grouped by how much water they absorb. Glazed vitrified tile sits in the lowest-absorption group, Group BIa, capped at 0.5% by the standard, though a well-made tile usually comes in well under that ceiling. Grifine's own tested water absorption sits below 0.2% across the range. A tile in this range holds up in wet areas, handles temperature swings without cracking, and won't take on moisture that later shows up as staining or efflorescence.
Check this number first, before finishing or sizing, whenever a tile is heading anywhere near water: bathrooms, kitchens, terraces, or building exteriors. A beautiful tile with the wrong absorption class in the wrong location isn't a design choice. It's a maintenance problem waiting for the first monsoon.
PEI rating is a traffic forecast, not a quality score
PEI rating gets treated like a badge of honour, as though a higher number always means a better tile. It doesn't work that way. PEI measures how well the glaze resists abrasion, on a scale from I to V. Class I and II suit walls and low-traffic residential floors: bedrooms, for instance, where footwear is soft, and traffic is light. Class III handles general residential use. Class IV is built for heavier residential traffic and light commercial spaces. Class V is for the busiest institutional and commercial floors: lobbies, retail corridors, anywhere the traffic barely stops.
Specifying PEI V for a private bedroom isn't wrong, exactly. It's just an unnecessary premium for a job PEI III would have done just as well. The reverse mistake costs more: a PEI III tile in a mall corridor shows wear inside a year. Match the rating to the traffic, not to the number that sounds strongest on paper.
The finish itself moves the number. Grifine's matt, structured matt, and carving ranges test at PEI IV. The polished range tests at PEI III because the mirror finish that gives a polished tile its shine also softens its resistance to abrasion. That's a reasonable trade in a formal lobby, seen mostly by dress shoes. It's a poor one on a loading dock.
Slip rating stops being optional once water shows up.
Slip resistance runs from R9 to R13 under the ramp-test standard that most glazed vitrified tile is measured against. R9 suits dry indoor floors. R10 handles occasional splashes: kitchens, entryways. R11 and above cover areas that see water regularly: bathrooms, pool surrounds, ramps, covered outdoor walkways. Each step up the scale trades a little surface smoothness for more grip.
This is the rating project teams get wrong most often, usually because a client falls for a high-gloss finish in a wet area. A glossy tile can carry a respectable PEI and water absorption number and still be genuinely hazardous underfoot the moment it's wet.
If the room sees water, condensation counts; the slip rating decides the spec, not the finish.
It's telling that polished glazed vitrified tile often carries no declared slip rating at all. Grifine's polished range doesn't, because a mirror finish and meaningful slip resistance pull in opposite directions: a tile can't be built for grip and for shine at the same time.
If a data sheet is silent on slip class, that silence is the answer, not an oversight. Matt and structured finishes are where the R-rating does its real work: Grifine's matt and carving range tests at R9, and the textured R11 range earns its name.
Modulus of rupture is the number that engineers actually check first
Modulus of rupture, or MOR, measures how much bending stress a tile can take before it fractures. It matters most for large-format work, raised flooring, and any application where the tile spans a gap rather than sitting flush on a fully bonded substrate.
A tile with a low MOR can look identical to a stronger one and still fail differently under the same load: hairline cracks first, then breakage at the corners under point load from furniture or foot traffic.
The regulatory floor for glazed vitrified tile is 35 N/mm². Grifine's matt, carving, and R11 ranges test above 40 N/mm², a real margin above the minimum, not a bare pass. The polished range, tested separately because the surface treatment changes how the tile performs under load, clears the same 35 N/mm² floor.
For a structural engineer signing off on a project, MOR is usually the first number checked, well before finish or colour enters the conversation.
A spec line that survives an argument
A BOQ entry that reads "glazed vitrified tile, 60×120cm" isn't a specification. It's a description. It leaves every performance question open, and open questions are exactly what get renegotiated on-site during a dispute over which tile was actually promised.
A specification that holds up looks more like this: glazed vitrified tile, 60×120cm, matt finish, water absorption <0.2% (Group BIa per ISO 13006 / EN 14411), PEI IV, slip class R9, modulus of rupture >40 N/mm². Every term in that line is testable. If a contractor substitutes a cheaper tile, the numbers expose it immediately; there's nothing left to argue about.
What this looks like on a Grifine data sheet
Grifine tests every finish separately, because a matt surface, a polished surface, and a textured R11 surface don't perform identically even when they come off the same tile body. Water absorption holds under 0.2% across the range. Breaking strength runs above 1500N against a 1300N regulatory floor. Stain resistance is declared at class 5 for matt and R11, class 4 for polished, the same pattern as the PEI difference, because a smoother surface consistently trades some resistance for shine.
None of this is unique to Grifine. It's what a specifier should check on any glazed vitrified tile before it goes on a BOQ: dimensional accuracy, modulus of rupture, abrasion resistance, resistance to crazing, chemical and acid exposure, breakage, staining, frost. The reason to ask a manufacturer for this data isn't to interrogate them. It's so the number on the data sheet is still the number that shows up on-site, six months after the order is placed, and nobody quite remembers what was promised verbally.
That consistency, tile after tile, project after project, is what a specification is actually protecting. A spec sheet is only useful if the material performs the same way every time someone checks it against the number.
FAQ
What's the difference between PEI rating and slip rating?
PEI measures how well the glaze resists wear from foot traffic over time. Slip rating measures grip underfoot, especially when the surface is wet. A tile can score well on one and poorly on the other; they're unrelated properties, and both need checking separately.
Is a higher water absorption number ever acceptable for flooring?
For most modern glazed vitrified tile flooring, no. Anything meaningfully above 0.5% absorption opens the door to staining and freeze-related damage in exterior applications, even when the tile looks identical on the surface.
Which number matters most for large-format slabs?
Modulus of rupture, alongside thickness. Large-format tile spans more unsupported area during handling and installation, so a low MOR shows up as breakage well before it becomes a wear problem on-site.
Can I ask a manufacturer for the test data sheet before ordering?
Yes, and it's worth doing for any project above a few hundred square metres. A reputable manufacturer, Grifine included, has this documentation ready without needing to run new tests on request.
Does a higher PEI rating always mean a more expensive tile?
Generally, yes, since a harder, more abrasion-resistant glaze usually costs more to produce. That's exactly why matching the rating to actual traffic, rather than defaulting to the highest number, keeps a project on budget without compromising performance where it counts.
