The short answer
Porcelain paving is laid on a solid, well-drained build-up, not loose sand. Installers typically dig out to around 150–160mm below the finished patio height to allow for a compacted sub-base of about 100mm of MOT Type 1, a full bedding-mortar bed of roughly 40mm, and the 20mm slab itself. The key difference from natural stone is priming: because porcelain is non-porous, a priming slurry must be brushed onto the back of every slab so it bonds to the mortar — without it the slabs will not stick. Each slab is laid on a full bed, tamped level with a slight fall for drainage, and the joints are grouted once set to seal them against water and weeds. It is a more exacting method than stone, which is why it is laid by an installer who works with porcelain regularly.
Porcelain is laid differently from natural stone, and the difference matters for how long the patio lasts. Here is the method in plain English — the base build-up, the priming step and the grouting.
The method in brief
- Dig-out depth~150–160mm typical
- Sub-base~100mm compacted MOT Type 1
- Bedding bed~40mm full mortar bed
- Priming slurrybrushed on every slab back
- Jointsgrouted once set
The base build-up
A porcelain patio is only as good as the base under it. A typical build-up digs out to around 150–160mm below the finished level to take a compacted sub-base of about 100mm of MOT Type 1 (or similar), a full bed of bedding mortar of roughly 40mm, and then the 20mm slab. The base is compacted so it does not settle, and the patio is set with a slight fall — commonly around 1:80 — so rainwater drains away from the house rather than pooling. Standing water is the most common long-term frustration, so getting the falls right at this stage is what prevents it.
| Layer | Typical depth | Purpose |
|---|---|---|
| Compacted sub-base | ~100mm | stable, well-drained foundation |
| Bedding mortar (full bed) | ~40mm | supports the whole slab |
| Porcelain slab | 20mm | the finished surface |
| Total dig-out | ~150–160mm | below finished patio level |
Indicative build-up for guidance — your installer sizes it to your ground. Source: Pavestone porcelain installation guide.
Priming and grouting — the porcelain difference
The step that catches people out is priming. Porcelain is non-porous, so unlike stone it will not bond to bedding mortar on its own. A priming slurry is brushed onto the back of every slab — typically a thin even coat around 1–2mm — just before it is set onto the full mortar bed, which is what makes it stick. Each slab is tamped down with a rubber mallet and checked with a level so it is fully supported and does not rock. Once the bed has set, the joints are grouted to give a waterproof seal that keeps water out and weeds from growing between the slabs. Skipping the primer or laying on dabs rather than a full bed is the usual cause of loose or hollow-sounding slabs later.
Want it laid the right way?
We'll match you with a vetted patio installer who works with porcelain — full mortar bed, primed slabs, proper falls and grouted joints — and quotes the base build-up clearly.
Frequently asked questions
How is porcelain paving laid?
On a solid build-up: typically around 100mm of compacted MOT Type 1 sub-base, a full 40mm bed of bedding mortar, and the 20mm slab — usually a dig-out of around 150–160mm. A priming slurry is brushed onto the back of every slab so it bonds, then the joints are grouted once set.
Why does porcelain need a priming slurry?
Because porcelain is non-porous, it will not bond to bedding mortar on its own. A priming slurry brushed onto the back of each slab creates the bond — without it, the slabs can come loose. It is the main way laying porcelain differs from natural stone.
Can porcelain be laid on sand like some slabs?
No. Outdoor porcelain needs a full bed of bedding mortar on a compacted sub-base, not loose sand or spot dabs. Laying it correctly with priming and proper drainage falls is what stops it lifting or pooling water later.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific garden. They are guidance, not a quotation.