How to lay a porcelain patio

Video by Marshalls. This guide draws on the tutorial “How to lay a porcelain patio” from the Marshalls Gardens and Driveways YouTube channel, published in 2023. Marshalls supply a huge range of outdoor porcelain and have a thorough understanding of how it needs to be laid. Their demonstration of the adhesive mortar technique — and why you should not use an ordinary sand-and-cement bed with porcelain — is the most useful part of the video.

1. Plan your layout and order the slabs

Work out the area and sketch the slab layout to scale. Porcelain typically comes in large format sizes — 600×600 mm, 600×900 mm, and 900×900 mm are all common. Larger slabs look impressive but require a flatter, better-prepared base than smaller ones, because any unevenness is more obvious.

Allow 10–15% extra for cuts. Porcelain cuts cleanly with a diamond blade angle grinder or a wet tile saw, but wastage on awkward shapes adds up. Order slightly more than you think you need — buying a second batch of a discontinued shade never ends well.

2. Excavate and compact the sub-base

Porcelain cannot flex, so the base must be genuinely rigid. Excavate to around 200–250 mm below finished level: 150 mm for compacted Type 1 MOT sub-base, 50–75 mm for a concrete slab or wet mortar bed, and the thickness of the tile itself.

For larger patios, a concrete slab rather than a plain mortar bed is the better choice. Porcelain laid on a concrete slab is far less likely to crack or move over time. Compact the Type 1 thoroughly with a plate compactor before the concrete or mortar goes in.

3. Use an adhesive mortar, not ordinary sand and cement

This is the single most important difference between laying porcelain and natural stone. Porcelain has a non-porous, smooth back face that does not bond to a standard sand-and-cement mix. Use a flexible, polymer-modified tile adhesive mortar designed for outdoor porcelain — it is sometimes labelled as “paving adhesive” or “porcelain paving mortar”.

Apply a full coverage bed to the sub-base, then also back-butter the slab itself before laying. Both surfaces should be coated. Any uncoated area beneath a porcelain tile is a void waiting to fill with water, freeze, and crack the tile.

4. Set the drainage fall and establish your datum

Before laying a single slab, establish a datum point at the house wall and calculate the drainage fall required to the far edge of the patio. Aim for at least 1 in 80 — around 12 mm fall for every metre. Set string lines or use a laser level to keep the fall consistent across the whole area.

Large-format porcelain is very unforgiving of an inconsistent fall. A section that holds water will grow algae and become slippery, which defeats the point of choosing a low-maintenance surface. Getting the levels right at the start is much easier than trying to correct them later.

5. Lay the first slab from a fixed corner

Start from the most visible corner — usually the corner nearest the house. Spread the adhesive mortar, back-butter the first slab, and lower it carefully onto the bed. Use a rubber mallet and a full-length spirit level to bed it precisely to your datum level.

Do not slide slabs across the adhesive bed once they are down — this smears the adhesive and can push it into joints. Place, tap level, and leave. If a slab is significantly out, lift it and re-apply fresh adhesive rather than trying to work around the error.

6. Continue laying with consistent joint gaps

Use plastic tile spacers to keep the joint width consistent. Most outdoor porcelain looks best with joints between 3 mm and 10 mm, depending on the tile size and the jointing compound you intend to use. Check levels constantly with a spirit level — both across each individual slab and across the run.

Stagger the joints if you are using a rectangular format mix. Continuous joints across a large area look professional; random patterns can look messy if the cuts are not well planned. Work out the pattern on paper first.

7. Cut edge tiles accurately

Porcelain cuts cleanly with a diamond blade angle grinder or an electric tile saw with a water-cooled blade. Dry cutting creates dangerous silica dust — always use a wet blade or wear a suitable dust mask and work outside if cutting dry. Mark cuts clearly with a chinagraph pencil or chalk line.

Measure each cut individually rather than assuming all the edge cuts will be the same width. Walls, borders, and existing paving are rarely perfectly straight. Take individual measurements for each piece.

8. Point the joints and finish

Allow the adhesive mortar to cure for at least 24 hours before jointing. Sweep out any loose debris from the joints, then apply a suitable outdoor jointing compound. Flexible, polymer-modified jointing compounds are the right choice for porcelain — ordinary cement mortar is too rigid and will crack and crumble in short order as the slab edges expand and contract with temperature.

Apply the jointing compound with a squeegee or pointing tool, pressing it firmly into the joints, then clean the slab faces before the compound hardens. Porcelain is non-absorbent so cleaning is straightforward — a damp sponge and a clean rinse while the compound is still fresh will leave the surface looking excellent.

When to call a handyman

Laying a large-format porcelain patio is physically demanding and technically precise. The margins for error are smaller than with natural stone. Call Richard if the ground is complicated, if drainage is a concern, or if you want the job done correctly in one go rather than working it out on a trial-and-error basis. A patio laid badly will need lifting and relaying within a season.