Porcelain vs Stone Paving: Grip, Sealing and Upkeep

Porcelain vs stone paving is the decision most patio projects stall on, and it is usually argued on looks when the things that actually decide it are grip in the wet, how the slab behaves in a frost, and how much work it needs in year five. We lay both across Bromley and south east London, and neither is simply better. One is a manufactured product with a tightly controlled specification; the other is a natural material with variation built into it. Knowing which of those you want is most of the choice.

What porcelain and stone paving actually are

Outdoor porcelain is a fired ceramic slab, pressed and vitrified so that it absorbs almost no water. Under BS EN 14411 (and the equivalent ISO 13006), the porcelain group is BIa: water absorption of 0.5% or less. Outdoors it is normally supplied at 20mm thick rather than the 8mm to 12mm used indoors, because it has to span an imperfect mortar bed and take point loads from furniture legs.

Natural stone paving is quarried and cut, and is covered by a different standard: BS EN 1341:2012, which sets requirements and test methods for natural stone slabs used for external paving. The usual UK choices are Indian sandstone, limestone, granite, slate and porphyry, and we compare the materials themselves in porcelain vs natural stone tiles. Because it is a natural material, the standard deals in tolerances and declared values rather than a single fixed specification, and two slabs from the same pack will not be identical.

That difference runs through everything else. Porcelain gives you repeatability. Stone gives you variation, and variation is either the charm you paid for or the thing that annoys you, depending on what you expected.

Slip resistance: read the PTV, not the R rating

This is where most buyers are misled, and it is worth being blunt about it. Showrooms and websites advertise outdoor paving with an R rating, usually R11. That figure comes from DIN 51130, a German ramp test in which a person walks a sloped sample wearing cleated safety boots while the surface is contaminated with motor oil. It was designed for industrial floors. It is not a measure of how a wet patio behaves under a trainer or a bare foot.

Chart showing HSE pendulum test value bands: 0 to 24 high slip potential, 25 to 35 moderate, 36 plus low — The HSE slip potential bands that an R rating cannot be converted into. | Chart by Bromley Tilers

The measure UK guidance actually uses is the pendulum test value, or PTV, from BS 7976. The Health and Safety Executive sets the bands in its guidance note Assessing the slip resistance of flooring: a PTV of 0 to 24 is high slip potential, 25 to 35 is moderate, and 36 or above is low slip potential. BS EN 1341 takes the same line for external stone, treating a pendulum value above 35 as the generally safe mark.

The UK Slip Resistance Group is explicit that the pendulum and the DIN ramp test do not measure the same thing, and that a value from one cannot be converted into the other’s category. So an R11 sticker tells you very little on its own. Ask the supplier for a wet pendulum figure, tested with the Slider 96 rubber, and check it clears 36. We go into this in more detail in our piece on whether porcelain tiles are slippery.

Neither material wins outright. Textured, sawn or flamed stone and a grip-finish porcelain both test well; a polished surface of either does not. The common mistake is putting indoor-style polished porcelain outside, where it will be wet and shaded for months at a time.

Frost, water and what porosity costs you

Porcelain’s very low water absorption is why it copes with UK winters so easily: water it cannot take in cannot freeze inside it and spall the face off. It is also why porcelain does not really stain, as wine, barbecue fat and leaf tannin sit on the surface.

Stone is porous to varying degrees. Granite is dense and close to indifferent to weather. Sandstone and limestone are far more absorbent, which is why they darken when wet, hold algae in a shaded north-facing garden, and can keep a permanent shadow from an oil spill. It is also why a poorly bedded stone slab shows picture framing, the pale border left by salts drawn up through the joint.

None of that makes stone a bad buy. It means stone asks for a sealer and periodic cleaning, and porcelain largely does not.

Laying: porcelain is far less forgiving

Both materials are covered by BS 7533-102:2021, the code of practice for constructing pavements with modular paving units, which includes porcelain in both bound and unbound builds. The build-up is broadly the same: a compacted sub-base, then a full mortar bed, typically around 30mm to 40mm.

The critical extra step with porcelain is the slurry primer. Because the back of a porcelain slab is effectively non-absorbent, mortar has nothing to key into. A cement-based slurry primer has to be brushed onto the full underside of every slab and laid into wet mortar so the two cure together. Skip it, or prime only the corners, and the slabs will sound hollow and eventually lift. This is not optional detailing, it is the difference between a patio that lasts and one that fails in three winters.

Porcelain also needs a full bed with no voids, because a 20mm ceramic slab bridging a gap will crack under a point load where a sandstone flag would not. It takes a diamond blade to cut, too. The full sequence is set out in our step by step on laying outdoor porcelain paving.

Two rules apply whichever you pick. Build in a fall so water runs off: 1:80, or 12.5mm per metre, is the usual minimum, and many installers prefer 1:60 for porcelain because the surface is non-porous and every drop has to be moved by gradient alone. And keep the finished paving level well below the damp proof course. Approved Document C practice is at least 150mm; where that genuinely cannot be achieved on an existing house, 75mm is the absolute floor, with drainage to suit. A patio laid up to the brickwork is one of the most common causes of damp we get called to.

Planning permission and drainage

This catches people out on front gardens rather than back patios. Under permitted development for houses, laying more than five square metres of traditional impermeable surfacing in a front garden needs planning permission if the water cannot run to a permeable area. If the surface is permeable, or the rainwater is directed to a lawn or border to soak away naturally, no permission is needed. The rules do not apply to flats and maisonettes, and an Article 4 direction or a planning condition can remove the right entirely. The Planning Portal sets out the current position.

Both porcelain and stone are impermeable surfaces in this sense, so neither gets you out of it. What matters is where the water goes: a permeable jointing system, a gravel margin, or a fall onto a border will usually keep you inside permitted development.

Sourcing and ethics on natural stone

One point that rarely comes up in a showroom. Much of the sandstone laid in British gardens comes from Rajasthan, and child labour in those quarries has been documented for two decades. Marshalls was the first stone company to join the Ethical Trading Initiative, in 2006, and went on to audit its Indian supply chain and fund schooling in quarrying communities. The ETI’s own account of that work is published on its site.

If you buy natural stone, ask where it was quarried and whether the supply chain is independently audited. Reputable merchants answer that immediately.

Which one should you actually buy

Choose porcelain if you want a patio that looks the same in ten years as on day one, you have a shaded garden where algae is a recurring nuisance, or you are matching an indoor floor across a threshold. Accept that it costs more to lay properly and can look flat over a large area if you pick a heavily printed pattern.

Choose natural stone if you want depth and variation, or you have a period property where a uniform ceramic surface would look wrong. Accept that it needs sealing, that it will change colour, and that it wants a proper clean every couple of years.

On cost, porcelain is generally dearer once laying is included: the slurry priming, the cutting and the lower tolerance for a sloppy bed all add labour. Stone is cheaper to buy and quicker to lay, but carries a maintenance cost porcelain does not. Get both quoted on the same drawing, with the same build-up specified.

Frequently asked questions

Is porcelain paving slippery when wet?

Good outdoor porcelain is not, but you have to check the right number. Ask for the wet pendulum test value rather than the R rating, and look for 36 or above, which is the HSE’s low slip potential band. Polished or indoor-grade porcelain laid outside genuinely is slippery and should not be used.

Does porcelain paving need sealing?

No. With water absorption of 0.5% or less it has almost nothing for a sealer to penetrate, and sealing it can leave a residue on the surface. Natural stone, particularly sandstone and limestone, does benefit from a breathable impregnating sealer.

Can porcelain paving be laid on sand?

Not for a domestic patio. Twenty millimetre porcelain needs a full mortar bed with a slurry primer on the back of each slab so it bonds. Laid on sand it will rock, sound hollow and crack under point loads. Pedestal systems on a flat roof or balcony are a different case, but that is not a garden patio build.

Do I need planning permission for a patio?

A rear patio normally does not need permission. A front garden is different: more than five square metres of impermeable surfacing needs permission unless the water drains to a permeable area such as a lawn or border. Flats, maisonettes and properties under an Article 4 direction are not covered by the permitted development right.

How much fall does a patio need?

A minimum of 1:80, which is 12.5mm of fall for every metre, away from the house. On porcelain many installers use 1:60, because the slab absorbs nothing and all the water has to be moved by gradient. Build the fall into the sub-base and mortar bed rather than trying to correct it at the surface.

Getting it laid in Bromley

The specification matters more than the material. A stone patio laid on a full bed with the right fall will outlive a porcelain one dropped on five dabs of mortar. If you want either quoted properly, with the build-up written down, Bromley Tilers covers Bromley and south east London.

020 8058 5574

contact@bromleytilers.co.uk