How to Lay Porcelain Paving Slabs: UK Step-by-Step Installation Guide

How Do You Lay Porcelain Paving Slabs Correctly?

20 mm outdoor porcelain paving should normally be laid over a stable compacted sub-base on a continuous full mortar bed, with suitable slurry primer covering the complete underside of every slab. The installation also needs controlled drainage falls, consistent external joints and suitable porcelain cutting and jointing materials.

What Base Should Be Used Under Porcelain Paving?

For a conventional pedestrian patio over suitable ground, approximately 100 mm of compacted MOT Type 1 is a common UK starting specification. Weak, filled, waterlogged or otherwise unstable ground can require deeper excavation, geotextile separation or a specifically designed foundation.

How Thick Should the Mortar Bed Be for Porcelain Paving?

A full mortar bed of approximately 30–40 mm is commonly used over a correctly prepared patio sub-base. The mortar must provide continuous support after the slab has been tapped to level rather than leaving substantial voids beneath the porcelain.

Does Porcelain Paving Need Slurry Primer?

Yes. For conventional mortar-bed installation, suitable slurry primer should be brushed over the complete underside of every porcelain slab immediately before laying. Porcelain has very low water absorption, so primer provides the bonding bridge between the dense slab and fresh bedding mortar.

What Joint Gap Should Be Left Between Porcelain Slabs?

Around 5 mm is a practical joint width for many UK outdoor porcelain patios. Rectified slabs are sometimes installed within an approximate 3–5 mm range, but the paving manufacturer and selected jointing-product requirements should always be checked.

Can You Lay Porcelain Paving Yourself?

A competent DIY installer can lay a small, straightforward porcelain patio, but porcelain is less forgiving than many traditional paving materials.

The main difficulties are:

• creating a stable and accurately graded sub-base;
• cutting dense 20 mm slabs cleanly;
• maintaining full mortar support;
• applying complete slurry-primer coverage;
• keeping joints consistently aligned;
• forming reliable drainage falls;
• preventing cement, primer or grout residue from curing on the surface.

Professional installation is advisable where the site includes soft or made-up ground, retaining structures, drainage problems, low thresholds, large-format slabs, multiple levels, steps or extensive cutting.

Porcelain Patio Construction: Typical Build-Up

For a conventional pedestrian patio built over soil, the construction from the ground upwards will commonly include:

• Stable sub-grade: firm ground with vegetation, topsoil, roots and soft areas removed.
• Geotextile where required: a separation layer for suitable ground conditions, not a substitute for excavation or compaction.
• MOT Type 1: approximately 100 mm after compaction for a typical domestic pedestrian patio where ground conditions permit.
• Full mortar bed: generally around 30–40 mm.
• Slurry primer: continuous coverage across the complete underside of each slab.
• Outdoor porcelain paving: typically 20 mm thick.
• Exterior jointing system: compatible with the paving, joint width and site conditions.

The exact construction should reflect the ground and expected loading. Soft clay, filled ground, drainage trenches and areas exposed to heavier loads can require a deeper or specifically engineered base.

Tools and Materials Needed

Materials

• 20 mm outdoor porcelain paving slabs
• MOT Type 1 granular sub-base
• Sharp sand or washed concreting sand
• Cement
• Proprietary slurry primer suitable for porcelain
• Exterior porcelain grout or compatible jointing compound
• Clean water
• Tile spacers
• Suitable edge restraints where required
• Linear drainage channel where required

Current paving can be compared in the Porcelain Paving Slabs collection, while compatible bonding and jointing products are available in Slurry Primers and Jointing Compounds.

Tools

• Shovel, rake and wheelbarrow
• Tape measure, pegs, string lines and marker
• Long spirit level and straight edge
• Plate compactor
• Cement mixer
• Builder's trowel
• White or non-marking rubber mallet
• Electric paddle mixer
• Wide slurry-primer brush
• Wet bridge saw or suitable angle grinder with a porcelain-rated diamond blade
• Rubber grout float or grout gun, depending on the jointing system
• Clean buckets, sponges and microfibre cloths

How to Lay Porcelain Paving Slabs Step by Step

Step 1: Check the Slabs Before Laying

Inspect the paving when it arrives. Confirm the product, dimensions, quantity, surface finish, batch references and overall condition before installation begins.

Stone-effect porcelain usually contains a limited number of printed faces. Dry-lay slabs from several packs and distribute repeated graphics and tonal variation naturally across the area.

Do not install visibly damaged, incorrect or unacceptable slabs. Once a slab has been cut, primed or fixed, resolving a product issue becomes considerably more difficult.

Step 2: Plan the Layout and Cuts

Mark the patio perimeter and decide the laying direction before excavation.

Consider:

• doors;
• steps;
• inspection covers;
• drainage channels;
• walls;
• finished edges;
• cut positions.

Measure the area against the slab module, including the intended joint width. Moving the starting line can often avoid narrow cuts along a doorway or prominent edge.

Large-format slabs such as 900 × 600 Porcelain Paving make setting-out errors particularly visible, so establish square reference lines rather than assuming existing walls are perfectly straight.

Step 3: Set the Finished Level and DPC Clearance

The finished paving surface should normally remain at least 150 mm below the property's damp-proof course.

Do not cover:

• air bricks;
• weep holes;
• ventilation openings.

Low or level-access thresholds require a correctly designed drainage and waterproofing detail. Simply raising paving close to a doorway without appropriate drainage can increase the risk of water being directed towards the building.

Step 4: Establish the Drainage Fall

Porcelain absorbs very little water, so rain remains primarily on the surface until it drains away or evaporates.

The paving therefore needs a deliberate continuous fall towards a suitable discharge point.

For many conventional patios, approximately 1:60 is a practical working target. This represents around 17 mm of fall per metre, so a 3 m run would require approximately 50 mm of total drop.

Some installations can use a different fall depending on slab texture, flatness, site levels, drainage design and manufacturer guidance.

Do not assume a visually level patio will drain correctly. Establish the drainage line before constructing the base.

Step 5: Excavate the Patio Area

Excavate sufficiently to accommodate the full construction while maintaining the required finished level.

A typical combination of:

• 100 mm compacted Type 1;
• 30–40 mm mortar;
• 20 mm porcelain;

requires approximately 150–160 mm below the finished paving surface.

This is not a universal excavation depth. Remove topsoil, vegetation, roots and loose material until a stable sub-grade is achieved.

If the exposed ground pumps, deforms or allows a boot heel to sink easily, further excavation or ground improvement may be required.

Step 6: Install Edge Restraints and Drainage

Install required kerbs, edging units or rigid restraints before laying the main field of paving.

Unsupported mortar at an exposed perimeter can deteriorate and allow edge slabs to move.

Where water cannot drain safely into a suitable permeable area, install an appropriate channel drain or designed outlet.

Do not direct runoff towards the house or neighbouring property.

Step 7: Lay and Compact the MOT Type 1 Sub-Base

Spread MOT Type 1 in manageable layers.

For an approximately 100 mm compacted build-up, compacting in separate layers is preferable to placing the entire depth loose and attempting to compact it in one pass.

Use a plate compactor and make repeated passes in different directions.

Pay particular attention to:

• corners;
• perimeters;
• backfilled service trenches;
• areas beside drainage channels.

The finished sub-base should be firm, even and constructed broadly to the intended patio fall.

Step 8: Prepare the Full Mortar Bed

Porcelain paving should be installed on a continuous full mortar bed, not isolated spots, rings or dabs.

Full support distributes loads, reduces rocking and limits unsupported voids beneath the slab.

A commonly used site mix is approximately four parts sharp sand to one part cement.

Some proprietary systems use a different specification, so follow the relevant paving, primer and bedding-product instructions where applicable.

Add clean water gradually. The mortar should be moist, cohesive and workable.

• Too dry: the mix can crumble, resist compaction and fail to make full contact.
• Too wet: slabs can sink, slide or lose the required fall.

A bed thickness of approximately 30–40 mm is common, with local adjustment where necessary to maintain the finished levels.

Step 9: Mix and Apply Slurry Primer

Slurry primer is essential for a conventional mortar-bed porcelain installation.

Mix the proprietary product according to the manufacturer's instructions.

Apply it with a wide brush across the complete underside of the slab, including edges and corners.

Do not apply only stripes, spots or partial coverage.

Lay the slab while the primer remains wet and active. Dried primer does not provide the intended wet-on-wet bond.

Step 10: Lay Each Slab onto the Full Bed

Lower the primed slab squarely onto the fresh mortar and tap it evenly using a clean, non-marking rubber mallet.

Before moving to the next slab, confirm:

• the surface follows the required drainage fall;
• the slab aligns with the string lines and adjacent paving;
• the complete underside is properly supported.

During the first section, lift an occasional newly bedded slab immediately to inspect mortar transfer.

The underside should show near-complete support without substantial voids. If contact is poor, correct the mortar consistency or laying method before continuing.

Step 11: Maintain Consistent Joint Widths

Use suitable rigid spacers for exterior porcelain.

Do not butt-joint the slabs.

Rectified 20 mm porcelain is commonly installed with joints in the approximate 3–5 mm range. PSU generally uses around 5 mm for many UK patio installations because it provides practical tolerance and adequate jointing depth.

Check the selected jointing system's minimum width and depth before laying begins.

Step 12: Cut Porcelain Correctly

20 mm porcelain is very hard.

For repeated straight cuts, a suitable wet bridge saw with a porcelain-rated diamond blade normally gives the cleanest and most controlled result.

An angle grinder can be appropriate for limited or detailed cutting in experienced hands, but long straight cuts are harder to control.

Do not use a general masonry blade.

Support the slab fully, mark the cut accurately and feed the blade steadily. Forcing the cut increases vibration, heat and the risk of edge chipping.

Dry-fit cut pieces before priming and bedding them.

Step 13: Clean as You Work

Remove mortar, slurry primer and cement residue immediately with clean water and suitable sponges.

Change the water frequently rather than spreading a cement film over the paving.

Do not allow cementitious residue to cure on textured porcelain. The same surface texture that improves wet grip can retain installation residue.

Some products can benefit from an appropriate grout-release or temporary protective treatment during installation, but this should be tested and used according to the manufacturer's instructions.

Step 14: Allow the Mortar to Cure

Keep newly laid paving free from traffic until the bedding mortar has developed sufficient strength.

Protect the work from:

• frost;
• heavy rain;
• excessive heat;
• rapid drying.

There is no reliable universal curing period because temperature, moisture, mortar depth and product specification all affect strength development.

Follow the relevant manufacturer instructions and allow additional time during cold or damp UK weather.

Step 15: Fill the Porcelain Paving Joints

Before jointing, confirm that the bedding has cured sufficiently and the joints are clean and open to the required depth.

Use an exterior grout or jointing compound specifically compatible with porcelain, the selected joint width and the site conditions.

Fill the joints fully rather than creating a thin surface cap above an empty void.

Clean the paving at the stage specified by the jointing manufacturer. Excessive washing can weaken some cement-based grout systems or draw material from the joints.

How to Lay Porcelain Paving on an Existing Concrete Base

Porcelain can sometimes be installed over existing concrete where the slab is stable, sound, appropriately drained and free from significant structural movement.

The surface must be clean and compatible with the chosen exterior fixing system.

Depending on the specification, porcelain may be installed over suitable concrete using an exterior-rated flexible adhesive or another approved bonded installation system.

Existing structural or movement joints should not simply be bridged and concealed beneath the porcelain.

Can Porcelain Paving Be Laid on Sand, Soil or Pedestals?

Directly on Sand

No. A conventional permanent 20 mm porcelain patio should not normally be laid loose on building sand or sharp sand alone. Loose sand does not create the required bonded load-bearing construction.

Directly on Soil

No. Soil moves with moisture, frost and loading. Porcelain laid directly onto soil is likely to become unstable, rock or develop failed joints.

On Adjustable Pedestals

Some porcelain products can be installed on proprietary pedestal systems for roof terraces, balconies and raised patios.

This is a separate engineered installation method. Slab specification, support spacing, edge restraint, wind loading and pedestal design must all be appropriate for the application.

Porcelain Paving Installation Mistakes to Avoid

• Starting without checking batches, printed faces and slab condition
• Using an existing wall as the only setting-out reference
• Placing paving too close to the damp-proof course
• Blocking air bricks or drainage openings
• Constructing the patio without a continuous drainage fall
• Directing runoff towards the house
• Laying over topsoil, loose sand or uncompacted ground
• Compacting a deep sub-base in one loose layer
• Leaving exposed patio edges without adequate restraint
• Spot bedding or using mortar dabs
• Using excessively dry or wet mortar
• Applying primer only in patches
• Allowing slurry primer to dry before laying
• Leaving substantial voids under slabs
• Butt-jointing porcelain
• Using an unsuitable cutting blade
• Allowing cement residue to cure on the slab face
• Walking on or jointing the patio before sufficient curing
• Ignoring movement requirements around structures or large areas

For a dedicated explanation of failures and corrective prevention, see What Should You Avoid with Porcelain Paving?.

How Much Material Is Needed?

Material quantities depend on patio area, construction depth, compaction and layout.

• Porcelain: allow the measured area plus cuts and wastage. Around 8–10% is sensible for many straightforward projects, with approximately 10–15% for small or more complex layouts.
• MOT Type 1: calculate from the required compacted volume and allow for compaction. A 20 m² patio at 100 mm compacted depth represents 2 m³ of finished compacted sub-base.
• Mortar: calculate from area and average bed thickness. A 20 m² patio at 35 mm average depth represents approximately 0.7 m³ of installed mortar before waste and local adjustment.
• Slurry primer and jointing: use the manufacturer's stated coverage and include a sensible allowance.

Coverage figures are planning estimates rather than substitutes for an accurate site calculation.

Final Installation Checklist

• Finished level and DPC clearance checked
• Drainage route and fall established
• Ground excavated to stable material
• Sub-base compacted in layers
• Edges and drainage restrained correctly
• Full mortar bed used beneath every slab
• Slurry primer applied to the complete slab underside
• Slabs laid while mortar and primer remain fresh
• Alignment, fall and joint widths checked continuously
• Cement residue removed immediately
• Bedding allowed to cure before jointing
• Joints filled fully with a porcelain-compatible product

For product selection before installation, see the Outdoor Porcelain Paving Buying Guide.

Customers comparing porcelain with other patio materials can also browse the wider Paving Slabs collection or visit the Porcelain Paving FAQs.

Porcelain Paving Installation FAQs

Do porcelain paving slabs need slurry primer?

Yes, for a conventional mortar-bed installation. Porcelain has very low water absorption and does not form a dependable direct bond with ordinary bedding mortar. Apply suitable slurry primer over the complete underside immediately before laying.

What is the best base for porcelain paving slabs?

For a normal pedestrian patio over suitable ground, a stable sub-grade, approximately 100 mm of compacted MOT Type 1 and a continuous full mortar bed are commonly used. Ground conditions and expected loading can require a different specification.

What mortar mix should be used for porcelain paving?

A mix of approximately four parts sharp sand to one part cement is commonly used for a site-mixed full mortar bed. Follow any specific requirements supplied with the paving, primer or proprietary bedding system.

How thick should the mortar bed be?

Approximately 30–40 mm is common over a correctly prepared sub-base. The mortar must remain thick enough after levelling to provide full and continuous support beneath each slab.

What fall should porcelain paving have?

Approximately 1:60 is a practical target for many conventional UK patios, equal to about 17 mm per metre. The final fall should suit the paving surface, site levels and drainage design.

Can porcelain paving be laid over concrete?

Yes, where the concrete is sound, stable, appropriately drained and compatible with the selected exterior fixing system. Cracked, moving or poorly drained concrete should be corrected rather than concealed.

What joint width should be used for outdoor porcelain?

Rectified outdoor porcelain is commonly laid with joints of approximately 3–5 mm. Around 5 mm is practical for many UK patios, subject to the requirements of the slab and selected jointing product.

What blade is best for cutting 20 mm porcelain paving?

Use a high-quality diamond blade specifically suitable for porcelain. A suitable wet bridge saw generally provides the best control for repeated straight cuts.