Porcelain paving slabs provide a durable, frost-resistant and low-maintenance surface for UK patios and garden areas. However, porcelain has extremely low water absorption and does not naturally bond to an ordinary mortar bed. Correct ground preparation, full mortar support and a suitable slurry primer are therefore essential.
This Paving Slabs UK guide explains the complete installation process for 20 mm outdoor porcelain paving, including excavation, drainage, sub-base construction, mortar preparation, slurry priming, cutting, jointing and the most common installation mistakes.
Quick Installation Summary
- Keep the finished paving surface at least 150 mm below the property's damp-proof course.
- Provide a drainage fall of approximately 1:60 away from the building.
- Install approximately 100 mm of properly compacted MOT Type 1 sub-base.
- Use a full mortar bed made with approximately five parts sharp sand to one part cement.
- Apply slurry primer across the entire underside of every porcelain slab.
- Maintain consistent joints, normally between 3 and 5 mm.
- Use an appropriate exterior porcelain jointing compound or flexible grout.
Typical Porcelain Patio Construction
A standard porcelain paving installation normally consists of the following layers, constructed from the ground upwards:
- Stable sub-grade: firm natural ground with all soft spots and organic material removed.
- MOT Type 1 sub-base: approximately 100 mm after compaction.
- Full mortar bed: normally around 30 to 40 mm thick and mixed at approximately 5:1 sharp sand to cement.
- Slurry primer: applied across the complete underside of each slab immediately before laying.
- Outdoor porcelain paving: commonly 20 mm thick.
- Porcelain-compatible jointing material: applied after the bedding mortar has cured sufficiently.
This construction distributes weight evenly, reduces the risk of movement and provides continuous support beneath the paving. Porcelain should never be installed using isolated mortar dabs or spot bedding.
Tools and Materials Required
Materials
- 20 mm outdoor porcelain paving slabs
- MOT Type 1 sub-base
- Sharp sand or washed concreting sand
- Cement
- Suitable porcelain slurry primer
- Exterior porcelain jointing compound or flexible grout
- Clean water
- Tile spacers
Tools
- Shovel, rake and wheelbarrow
- Measuring tape, setting-out pegs and string line
- Spirit level and straight edge
- Plate compactor
- Cement mixer
- Builder's trowel
- Rubber mallet
- Electric paddle mixer
- Brush suitable for slurry primer
- Wet saw or angle grinder with a suitable porcelain blade
- Rubber grout float or grout application gun
- Clean buckets and tiling sponges
Suitable personal protective equipment should also be worn, including gloves, safety glasses, hearing protection, a suitable dust mask and protective footwear. Wet cutting is preferable where practical because it helps control dust and cool the cutting blade.
Step-by-Step Porcelain Paving Installation
Step 1: Inspect the Paving Before Installation
Check the paving as soon as it is delivered. Confirm the product, quantity, dimensions, colour and surface finish before installation begins.
Porcelain batch and shade references should also be checked. Slabs from different production batches may contain slight variations in colour or tone. Where appropriate, select slabs from several packs during installation to distribute the printed faces and natural-looking variation evenly across the patio.
Do not install visibly damaged or unsuitable slabs. Once paving has been laid, cut or treated, resolving a product issue becomes considerably more difficult.
Step 2: Plan the Layout and Finished Levels
Mark out the patio and plan the laying pattern before excavation. Consider doors, steps, drainage channels, inspection covers and the position of cut slabs.
Avoid narrow cuts along prominent edges wherever possible. Adjusting the starting position can often create a more balanced layout and reduce unnecessary cutting.
The completed patio should normally remain at least 150 mm below the property's damp-proof course. Air bricks, drainage openings and other ventilation points must not be covered or obstructed.
Step 3: Establish the Drainage Fall
Porcelain has very low water absorption, so rainwater remains on the surface until it drains away. The patio must therefore be constructed with a consistent fall away from the building.
Paving Slabs UK generally recommends a fall of approximately 1:60 for a conventional porcelain patio. This means a drop of approximately 10 mm for every 600 mm of horizontal distance.
For example, a patio extending 3 m from the property would require a total fall of approximately 50 mm. The exact drainage arrangement should reflect the site, surrounding levels and the intended discharge point.
Use pegs and a string line to mark the finished paving height. Check that water will drain towards a suitable garden area, drainage channel or other appropriate outlet, rather than towards the building.
Step 4: Excavate to the Required Depth
Excavate the area deeply enough to accommodate the complete construction build-up. A typical installation using 20 mm porcelain, a 30 to 40 mm mortar bed and approximately 100 mm of compacted Type 1 may require an excavation depth of around 150 to 160 mm below the planned finished level.
This is a general guide rather than a universal measurement. Soft ground, made-up ground, heavy clay, drainage requirements or higher expected loads may require deeper excavation and additional ground preparation.
Remove vegetation, roots, loose soil, organic material and other unsuitable material. The exposed sub-grade should be firm. If a heel sinks easily into the ground, further excavation or additional ground stabilisation may be required.
Step 5: Install and Compact the Sub-Base
Spread MOT Type 1 across the excavated area. Where the required depth is substantial, install and compact the material in layers rather than attempting to compact the entire depth in one operation.
Use a plate compactor across the full area and make repeated passes in different directions. Pay particular attention to edges, corners and previously excavated service trenches, as these areas are more likely to settle.
The finished sub-base should normally be approximately 100 mm thick after compaction. It should be firm, evenly compacted and formed to the same drainage fall required for the finished porcelain surface.
Step 6: Prepare the Full Mortar Bed
Prepare the bedding mortar using approximately five parts sharp sand or washed concreting sand to one part cement. Measure the materials consistently rather than estimating each batch.
Add clean water gradually until the mortar becomes firm, workable and cohesive. It should retain its shape while still allowing the slab to be tapped down to the required level.
- Mortar that is too dry: may be difficult to compact and may provide poor contact beneath the slab.
- Mortar that is too wet: may allow the slab to move, slide or sink after positioning.
Prepare enough mortar for one manageable working area at a time. Do not allow the mortar surface to dry before the primed slab is installed.
Step 7: Mix and Apply the Slurry Primer
Slurry primer is essential when installing porcelain paving. Because porcelain is dense and non-porous, it will not reliably bond to an ordinary sand and cement bed without a suitable bonding layer.
Mix the slurry primer with clean water in accordance with its product instructions. Use an electric paddle mixer to produce a smooth and consistent mixture without dry powder or lumps.
Place the slab face down on clean timber supports and apply the slurry primer across the entire underside. Work right up to every edge and corner. No clear or untreated areas should remain.
Install the slab while the primer remains wet and active. Do not allow the primer to dry before the slab is placed onto the mortar bed.
Slurry primer can bond strongly to the decorative surface. If any material reaches the face of the slab, remove it immediately using clean water and a clean sponge.
Step 8: Lay the Slab on a Full Mortar Bed
Spread enough mortar to support the complete slab. Roughen the surface slightly with a trowel to help the slab compress into the bed without trapping large voids.
Carefully lower the primed slab into position without striking the edges of adjacent slabs. Tap it down evenly using a clean rubber mallet.
Check the slab with a spirit level, straight edge and string line. Confirm that it follows the intended drainage fall and sits evenly with the surrounding paving.
The mortar must support the complete underside of the slab. During the early stages of installation, lift an occasional slab to confirm that full contact is being achieved. If substantial voids are visible, correct the bedding method before continuing.
Step 9: Maintain Alignment and Joint Widths
Use suitable spacers to maintain consistent joints. Porcelain paving should not be installed with the edges touching.
A joint width of approximately 3 to 5 mm is commonly used for rectified outdoor porcelain paving. Paving Slabs UK generally considers approximately 5 mm a practical joint width for many UK patio installations, although the paving and jointing product instructions should always be checked.
Regularly inspect the laying lines from different directions. Small alignment errors can become much more noticeable across a large patio.
Movement joints may be required around fixed structures, where the patio meets the building, over existing structural joints or across large uninterrupted areas. Project-specific advice should be obtained where movement is likely.
Step 10: Cut and Dry-Fit the Porcelain
Use a suitable porcelain diamond blade with a wet saw or appropriate cutting tool. Measure carefully and mark each cut clearly before starting.
Allow the blade to cut at a controlled speed. Forcing the slab through the blade increases the risk of chipping, overheating and inaccurate cuts.
Dry-fit cut pieces before applying primer and mortar. Avoid very narrow pieces where possible, particularly along doorways, steps and highly visible patio edges.
Step 11: Clean the Surface During Installation
Remove mortar, primer and cement residue from the slab face while the material is still fresh. Keep a bucket of clean water and a clean sponge close to the working area.
Do not leave cement-based residue to harden on the porcelain surface. Dried residue can be difficult to remove and aggressive cleaning methods may damage the joints or surrounding materials.
Step 12: Allow the Bedding Mortar to Cure
Leave the installed paving undisturbed while the mortar develops sufficient strength. Prevent foot traffic and protect the area from heavy rain, frost, excessive heat or other adverse conditions.
Curing time depends on temperature, moisture, mortar composition and site conditions. Follow the relevant product guidance and allow additional time during cold or damp weather.
Step 13: Prepare and Fill the Joints
Before jointing, ensure the paving surface is clean and the joints are free from dust, loose mortar and standing water. Moisture within the joints may affect some grout colours and curing performance.
Use an exterior jointing compound or flexible grout that is specifically suitable for porcelain paving and the selected joint width. Mix and install the product according to its instructions.
Fill each joint to its full working depth. Do not create a thin surface cap over an empty or partially filled joint.
Remove excess material at the correct stage using a rubber float or clean tiling sponge. Avoid excessive washing, as too much water can weaken some cement-based grouts or affect the final colour.
Common Porcelain Paving Installation Mistakes
- Installing paving too close to the property's damp-proof course
- Failing to provide a consistent drainage fall
- Laying directly onto soil, loose sand or an unstable base
- Installing an insufficient or poorly compacted sub-base
- Using mortar dabs or spot bedding instead of a full mortar bed
- Using mortar that is excessively dry or wet
- Failing to apply slurry primer to the complete underside
- Allowing the slurry primer to dry before laying
- Leaving substantial voids beneath the slabs
- Installing slabs with no joints between them
- Mixing unapproved porcelain batches without checking shade variation
- Using unsuitable cutting equipment
- Leaving cement or primer residue on the slab surface
- Walking on the paving or jointing it before the bedding mortar has cured
Professional Installation Advice
Porcelain paving is dimensionally precise and highly durable, but it is less forgiving of poor installation than many traditional paving materials. An unstable sub-base, inadequate mortar coverage or missing slurry primer may not be immediately visible, but can later result in movement, rocking slabs, failed joints or loss of bond.
Where the ground is soft, the drainage arrangement is complicated or the patio meets important building details, Paving Slabs UK recommends obtaining advice from an experienced paving installer before work begins.
Porcelain Paving Installation FAQs
Do porcelain paving slabs need slurry primer?
Yes. Porcelain has extremely low water absorption and does not reliably bond directly to an ordinary mortar bed. A suitable slurry primer should be applied across the complete underside of each slab immediately before laying.
Can porcelain paving be laid directly on sand?
No. A conventional 20 mm porcelain patio should be supported by a properly constructed sub-base and a continuous full mortar bed. Loose sand alone does not provide the bonding or structural support required for a permanent installation.
What sand and cement ratio should be used for porcelain paving?
Paving Slabs UK recommends approximately five parts sharp sand or washed concreting sand to one part cement for a conventional full mortar bed. The water content should be adjusted gradually to produce a firm but workable consistency.
How thick should the mortar bed be?
A mortar bed of approximately 30 to 40 mm is commonly used over a properly prepared sub-base. The exact thickness depends on site levels and ground preparation, but the bed must provide full and continuous support beneath every slab.
How much Type 1 is required beneath porcelain paving?
A typical pedestrian patio normally uses approximately 100 mm of compacted MOT Type 1. Soft ground, made-up ground or areas exposed to greater loads may require a deeper or differently engineered base.
What drainage fall should a porcelain patio have?
A fall of approximately 1:60 is commonly suitable. This provides around 10 mm of drop for every 600 mm of horizontal distance. Water should drain away from the property towards a suitable outlet.
How far below the damp-proof course should paving be?
The finished paving surface should normally remain at least 150 mm below the property's damp-proof course. Air bricks and other ventilation or drainage openings must also remain unobstructed.
What joint width should be used for outdoor porcelain paving?
Rectified outdoor porcelain paving is commonly installed with joints between 3 and 5 mm. Approximately 5 mm is a practical choice for many UK patios, subject to the paving and jointing product instructions.
Can porcelain paving be butt-jointed?
No. The slabs should not be installed with their edges touching. Butt-jointing provides no practical allowance for installation tolerances or movement and may increase the risk of damaged edges and failed joints.
How soon can porcelain paving be jointed?
Jointing should only begin after the bedding mortar has cured sufficiently. The required time varies with temperature, weather, mortar composition and product instructions. Additional curing time may be required in cold or damp conditions.
Final Summary
A durable porcelain patio begins below the visible surface. Stable ground, approximately 100 mm of compacted MOT Type 1, a full 5:1 sharp sand and cement mortar bed, complete slurry primer coverage and correctly filled joints all contribute to long-term performance.
By maintaining the correct finished height, providing a drainage fall of approximately 1:60 and avoiding spot bedding or unprimed slabs, porcelain paving can provide a stable, clean and low-maintenance outdoor surface for many years.
