How to Lay Granite Paving Slabs – Complete Installation Guide for UK Gardens
Granite paving has long been regarded as one of the most dependable and enduring choices for British gardens. Its strength, density and refined finish give patios and paths a crisp, long-lasting appearance rooted in traditional craftsmanship. To help you get the best from your granite paving slabs, this guide explains a traditional, rigid-lay method suitable for the UK climate.
1. Preparing the Area
1.1 Check the sub-base condition
A sound, well-compacted sub-base is essential for long-term stability. Before laying any granite slabs, confirm that the sub-base has been properly constructed.
- Patios and pathways: Typically use 100–150 mm of compacted Type 1 MOT (or 803/804).
- Areas with higher loads or vehicle overrun: May require a stronger sub-base such as CBM/HBM or dense bitumen macadam (DBM), designed to suit the expected traffic.
The sub-base should be firm underfoot, free from soft spots and levelled ready to receive the bedding layer.
1.2 Establish falls and levels
Granite paving should always shed water away from buildings and structures. A traditional, reliable fall is between 1:80 and 1:100, which provides effective drainage without creating a visibly steep slope.
- Set up taut string lines to mark the finished surface level and fall.
- Check heights at several points to avoid dips or humps.
- Plan the layout so that water runs towards suitable drainage points and does not pool on the surface.
1.3 Edge restraints
Rigid paving systems rely on secure edges to prevent movement over time.
- Install concrete edge beams, kerbs or solid edging blocks around the perimeter where required.
- Haunch them in strong concrete and allow them to firm up before laying the main field of paving.
- Well-built edge restraints help to keep lines straight and the whole patio locked together.
2. Bedding Layer (Laying Course)
Granite paving slabs should not be laid directly on sand, and spot-bonding should always be avoided. A full mortar bed provides the strength and support needed for long-term performance.
2.1 Mortar mix and consistency
A traditional and dependable mortar for granite paving is:
- Mix: 4 parts sharp sand to 1 part cement.
- Consistency: Firm, slightly damp – similar to wet earth, not sloppy.
The bedding layer is usually around 30–40 mm thick, depending on slab thickness and the tolerances in the base. Specialist external paving mortars or BS 7533-compliant bedding materials can also be used for higher performance or heavier traffic areas.
2.2 Screeded bed vs individual beds
If the granite slabs are calibrated with tight thickness tolerances (typically within ±2 mm), the laying course can be screeded to a uniform level before laying. Where thickness varies more, it is better to form individual beds and adjust each slab carefully to the correct height.
3. Apply a Slurry Primer (Bond Bridge)
Because granite is dense and relatively non-porous, it does not bond well to mortar without a primer. A slurry coat or bond bridge is therefore strongly recommended for a secure, long-lasting installation.
- Use an SBR-modified cement slurry or a proprietary external paving primer.
- Brush the slurry onto the entire underside of each slab immediately before laying.
- Avoid leaving bare patches – the whole back of the slab should be covered.
- Wipe away any drips from edges before they dry to prevent visible staining.
This step greatly reduces the risk of debonding, hollow sounds and future failures.
4. Laying the Granite Paving Slabs
4.1 Positioning the slab
Once the mortar bed and slurry primer are ready, each slab can be laid.
- Lower the slab carefully onto the mortar bed rather than dropping it into place.
- Slide it slightly to help the mortar and primer bond together and eliminate air pockets.
- Handle the slabs with care to avoid chipping arrises or corners.
4.2 Tapping down and levelling
Use a non-marking rubber mallet to bed the slab down firmly.
- Tap evenly across the surface to bring the slab to the correct level and fall.
- Check with a spirit level and straightedge as you go.
- Maintain a consistent joint width, typically around 5–10 mm for sawn granite, unless the design calls for something different.
- Ensure the slab is fully supported with no voids in the bedding.
4.3 Working to lines
It is good practice to work from a stable reference edge or corner.
- Follow your string lines for both direction and fall.
- Lay course by course, keeping joints straight and alignment tight.
- Check levels regularly across the whole area, not just along a single run.
5. Jointing and Finishing
5.1 Choosing a jointing material
Once the bedding mortar has hardened sufficiently (usually the following day), the joints can be filled. Suitable products include:
- Ready-mixed exterior jointing compounds.
- Polymerised or stabilised jointing sands (for certain rigid systems).
- Resin-based mortars.
- Traditional cement-based mortars (used carefully to avoid staining the slab surface).
5.2 Filling the joints
Follow the manufacturer’s instructions for the specific jointing product used.
- Make sure the joints are clean and free from loose debris.
- Work the jointing material well into the gaps to ensure they are fully packed.
- Compact the material and strike or smooth the joints to the required finish.
- Clean the surface of the granite as you go to prevent residue from hardening on the face.
6. Cleaning, Sealing and Aftercare
6.1 First clean after installation
When the paving is fully set:
- Rinse with clean water and, if necessary, a mild stone-safe cleaner.
- Avoid strong acids or harsh chemicals, which can damage the stone or pointing.
- Remove any remaining primer or cement film before it becomes stubborn to shift.
6.2 Sealing the granite (optional but recommended)
High-quality granite is naturally durable, but a breathable impregnating sealer can make day-to-day maintenance easier, particularly on lighter colours.
- Choose a sealer suitable for external granite paving.
- Apply only after the paving and joints have fully cured, following the product instructions.
- Sealing helps to resist staining, algae growth and general weathering.
6.3 Routine maintenance
With correct installation, granite paving should give decades of service with minimal upkeep.
- Brush regularly to remove leaves, dirt and debris.
- Wash the surface from time to time to discourage algae and lichen.
- Inspect joints annually and repair or top up where necessary.
- Avoid the use of metal shovels or aggressive tools that may scratch the surface.
7. Common Mistakes to Avoid
- Laying granite directly on sand or using a very thin bedding layer.
- Spot-bedding (dabs of mortar) instead of a full, continuous mortar bed.
- Omitting the slurry primer or using weak, unsuitable bonding agents.
- Failing to provide an adequate fall, leading to standing water on the patio.
- Using bedding mortar that is too wet, which can lead to settlement and poor support.
- Allowing slurry or mortar to harden on the slab surface and cause staining.
- Jointing before the bedding has properly set, which can disturb levels and weaken the bond.
8. Final Thoughts
Granite paving is a traditional, long-lasting choice for British gardens. Installed on a solid, well-compacted base with a full mortar bed and a proper bond bridge, it provides a stable, elegant surface that can last 40–50 years or more. By following the rigid-lay method outlined above, you can ensure that your granite patio or path not only looks the part, but also performs exactly as it should for many years to come.