Porcelain paving,
laid to stay flat.
Twenty-millimetre external porcelain, full-bedded and primed — the build-up that decides whether a patio is still level in ten years.
Porcelain has become the default surface for London gardens for a straightforward reason: it absorbs almost no water. A vitrified 20mm external tile sits at well under 0.5% water absorption, which means frost cannot get inside it and lift it, moss cannot root in it, and wine, barbecue fat and leaf tannin sit on the surface instead of soaking in. It never needs sealing, and it does not weather to a different colour than the piece next to it.
That durability is entirely dependent on how it is laid. Porcelain is non-porous on its underside as well as its face, so a mortar bed alone has nothing to grip — the slab has to be primed with a slurry bond, and it has to be laid on a full wet bed with no voids underneath. Spot-bedding a porcelain slab on five dabs of mortar is the single most common reason a patio starts rocking, drumming underfoot or cracking through the middle within a couple of seasons. There is no way to see the difference on the day it is finished.
Underneath that, the base does the structural work. A patio build-up runs down to firm formation, over a separation geotextile, with a compacted sub-base laid and whacked in layers rather than dumped to depth in one go. On London clay this matters more than on most ground, because clay shrinks in a dry summer and swells again in winter — a shallow base moves with it and takes the paving along.
Materials
- 20mm external porcelain
- The standard for garden paving. Near-zero water absorption, so it is frost-proof, does not stain and never needs sealing.
- Stone and timber effect
- Digitally printed surfaces that hold their colour where real stone weathers and real timber greys and splinters.
- Large format
- 600×1200 and larger reads calmer in a small garden — fewer joints, less visual noise. It needs a flatter base and full bedding to sit right.
- R11 slip rating
- Worth specifying for steps, thresholds and anything near water. Smooth indoor-grade tile outdoors is genuinely dangerous in a wet London winter.
How it is built
- Excavate to formationDown to firm ground, not to whatever depth is convenient.
- Sub-baseCompacted in layers over a separation membrane, to a depth set by the ground we find.
- Prime and bedPorcelain is non-porous, so every slab is primed with a slurry bond and laid on a full wet mortar bed — spot-bedding is the reason tiles come loose.
- Set out and cutLaid out dry first so cuts land where they should and the joints run true.
- Point and cleanBrush-in or slurry jointing, then washed down before the residue cures.
What decides the specification
The things that change the answer on a London job — and that nobody can judge from a brochure.
London clay and seasonal movement
Most of inner and south London sits on London Clay, which is a shrink–swell soil. It changes volume with moisture, and it does so most severely near mature trees drawing water out of it. That drives sub-base depth, and near a large tree it can mean the terrace needs to be structurally independent of the ground beneath it.
Falls and where the water goes
A terrace needs roughly a 1:80 fall to shed water, run away from the building, and finish at least 150mm below the damp-proof course unless a drainage channel is built in at the threshold. Level-threshold doors — very common on London rear extensions — always need a linear channel drain; there is no way to fall away from a flush door without one.
Surface water and the sub-base
Paving over what used to be lawn removes somewhere for rain to go. Where the terrace is large or the garden already sits wet, water is taken to a soakaway or a permeable margin rather than pushed onto the neighbouring plot, which is both a drainage failure and a boundary dispute.
Slip rating, and where it actually matters
Specify R11 or better for steps, thresholds, shaded north-facing terraces and anything near water. Smooth indoor-grade porcelain used outdoors is genuinely dangerous in a wet London winter, and the rating is a property of the tile that cannot be added afterwards.
Format, and what it does to a small garden
600×1200 and larger reads calmer in a compact space — fewer joints means less visual noise, and the eye stops counting slabs. Large format is less forgiving to lay: it needs a flatter bed and full support, because any void under a long slab becomes a crack.
Access
A rear London garden is often reached only through the house or a side return. That governs slab size, whether a mixer can get in, and how spoil leaves — and it is the single factor most often missed when a patio is priced over the phone.
What it costs
Every garden is priced from its own survey, because the cost is decided by things that are invisible until the ground is opened: how far the spoil has to be carried, what the existing sub-base is made of, whether levels have to be built up or cut away, and how the site drains. We quote after measuring, not before.
Book a free site surveyPorcelain Paving, answered.
Does porcelain paving need sealing?
No. External porcelain is vitrified, with near-zero water absorption, so there is nothing for a sealer to penetrate. The exception is the jointing compound between the slabs and any natural stone used alongside it — those may need attention, but the porcelain itself does not.
Can porcelain paving be laid over an existing patio?
Only rarely, and it is usually a false economy. The existing surface has to be structurally sound, correctly falling and low enough that the new build-up still finishes 150mm below the damp-proof course. Most existing patios fail at least one of those, and laying over a base that is already moving simply transfers the problem to the new surface.
Why does porcelain have to be primed before laying?
Because the underside of a porcelain slab is as non-porous as the face. Mortar cannot key into it mechanically the way it does with natural stone, so a slurry primer is painted on to create the bond. Without it the slab is resting on the bed rather than fixed to it, which is what produces hollow-sounding, rocking and eventually cracked paving.
Is porcelain slippery when wet?
External porcelain is manufactured with a textured surface and a slip rating — R11 is the usual specification for garden use. It is the indoor-grade tile, used outside because it matched the kitchen floor, that becomes hazardous. Ask what the rating of the specific tile is, not whether porcelain in general is slip-resistant.
Do I need planning permission for a patio?
A patio at ground level in a rear garden is normally permitted development. It becomes more complicated if the garden is in a conservation area, the property is listed, the terrace is raised more than 300mm above ground level, or a planning condition on a previous extension restricts it. Raised terraces also raise overlooking considerations with neighbours.
Porcelain Paving across all 32 boroughs.
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