Natural Stone Paving: Sandstone vs Slate vs Granite, Bed Thickness, Pointing Mixes and Sealing

Quick Answer: Indian Sandstone is the most popular UK natural stone paving choice: laid on a full mortar bed 25–30mm thick (semi-dry mix 6:1 sand:cement), pointed with a 4:1 weak mortar or specialist slurry pointing products. Granite setts are bedded 25–35mm on mortar. Slate paving requires 20–25mm bed. All natural stone on driveways needs minimum 100mm Type 1 sub-base beneath the mortar bed. Sealing is optional but protects against staining.

Summary

Natural stone paving — primarily imported Indian Sandstone but also limestone, granite, slate, and travertine — became dominant in UK gardens and patios from the early 2000s. It remains popular because of its genuine variation in colour and texture, its premium aesthetic, and the perception (often accurate) that it will outlast man-made alternatives if properly installed.

However, natural stone has specific installation requirements that differ from concrete block paving. The most important difference is the bedding method: natural stone must be laid on a full mortar bed, not a sand bed. Spot (five-spot) bedding — placing mortar only at the corners and centre of each stone — causes hollow spots under the stone which flex and crack under load, eventually causing the stone surface to break or the stone to rock. This is the most common installation failure in natural stone paving.

Pointing is the other critical area. Mortar pointing that is too strong (high cement content) is brittle and cracks as the slab moves under temperature cycles and ground movement. The correct mix is weaker than most people expect.

Understanding stone type, sourcing, bedding method, pointing mix, and sealing options is essential for anyone working regularly with natural stone paving.

Key Facts

Quick Reference Table

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Stone Type Hardness Typical Use Min. Driveway Thickness Frost Resistance
Indian Sandstone Medium Patios, paths, light driveways 30–40mm Good (varies by quarry)
Granite (setts) Very hard Driveways, commercial 50–100mm Excellent
Slate (riven) Medium-hard Patios, paths Not recommended for vehicles Moderate
Limestone Soft-medium Patios only Not recommended for vehicles Poor (porous)
Sandstone (Yorkstone) Hard Driveways, paths 40–50mm Excellent
Travertine Soft-medium Covered areas, conservatories Not recommended externally (porous) Poor
Pointing Mix Sand:Cement Ratio Application
General patio pointing 4:1 sharp sand:cement Standard patio stone, sheltered
Exposed/driveway pointing 3:1 sharp sand:cement Wind, heavy rain, vehicle areas
Specialist dry-pack mortar Product-specific Easier to use, consistent results
Traditional lime pointing NHL 2.5 or 3.5 + sand, 1:3 Listed buildings, heritage applications

Detailed Guidance

Stone Selection

Indian Sandstone — The workhorse of UK patio installation. Imported primarily from Rajasthan, it comes in consistent calibrated thicknesses (20mm, 22mm, 38mm, 44mm) for easy laying. Common colour groups:

For driveways, specify 38–44mm calibrated Indian Sandstone. 20–22mm is insufficient under vehicle tyres.

Yorkstone (British Sandstone) — Quarried in Yorkshire and Lancashire. Much harder and more consistent than Indian sandstone, and genuinely frost-resistant due to UK climate adaptation. The premium choice for durability but significantly more expensive than Indian sandstone. Natural riven or sawn faces available.

Granite — Imported or UK-quarried. Technically the most durable natural stone for external use. Granite setts (small rectangular blocks, typically 100×100×100 or 200×100×50) are the traditional UK street paving material. Resistant to frost, heavy loads, and chemical staining. Difficult to cut accurately without a wet tile saw. Much heavier than sandstone.

Slate — Riven (natural split) slate gives a textured non-slip surface suitable for paths. Smooth sawn slate is too slippery for external use when wet. Not suitable for vehicle areas — too thin and brittle under concentrated point loads. Welsh slate (Penrhyn, Delabole) is higher quality and longer-lasting than Chinese imports.

Sub-Base and Preparation

The sub-base specification is the same as for block paving (100mm Type 1 MOT), but natural stone has one additional step: a concrete or mortar blinding layer over the sub-base.

Blinding — A 50–75mm layer of C20 concrete (or lean mix concrete 8:1) laid over the sub-base provides a rigid working platform. Allow to cure 24–48 hours before applying mortar bed. Blinding prevents the semi-dry mortar bed from mixing with the granular sub-base, and provides a consistent base for setting out levels.

Some installers omit blinding and lay the semi-dry bed directly on compacted sub-base. This is acceptable for patio areas but not recommended for driveways.

Laying Method

Semi-dry mortar bed — Mix 6 parts sharp sand to 1 part Portland cement; add just enough water to achieve a damp crumble consistency (squeeze in hand, holds shape, does not drip). This is NOT the same as a wet screed. The semi-dry bed allows minor adjustment of individual stones while remaining firm enough to hold them.

Screeding the bed — Screed the mortar bed to the required depth across the working area using parallel screed rails. Bed depth allows for the stone thickness: finished level = bed depth + stone thickness.

Laying stones — Place each stone onto the semi-dry bed, press and tap firmly with a rubber mallet. Check for full contact: if the stone rocks or sounds hollow, lift and adjust the bed. For large slabs (600×600mm or larger), the semi-dry bed must be fully supporting all four corners and centre.

Bond pattern — Stretcher bond (staggered joints) is most common. Random rectangular (three or four sizes mixed) gives the most natural appearance and is typical for Indian sandstone. Keep joint width consistent: 8–12mm for natural stone is typical.

Cutting — Wet tile saw gives the cleanest cuts on sandstone and granite. Angle grinder with diamond disc also works. Safety: silica dust from stone cutting; same controls as block cutting — wet cutting preferred, FFP3 if dry cutting (see block paving installation for full COSHH guidance).

Pointing

Allow the laid stone to set for at least 24–48 hours before pointing, so stones don't move during the pointing process.

Semi-dry pointing — Mix 4:1 sharp sand:cement; dry enough to pack with a pointing iron or trowel. Press firmly into the joint with a pointing iron, ensuring no voids. Brush off excess with a stiff brush. This is the traditional method.

Dry-pack jointing mortars (EasyJoint, Rompox Traffic, Sandstone Fix) — Pre-mixed, brush-in products that require only water activation. Easier to use, generally consistent results. Some are suitable for driveways (check load rating). Product-specific application instructions must be followed.

Crucial rules:

Sealing Natural Stone

Why seal? — Sealing reduces water absorption, prevents oil and vehicle fluid staining, reduces biological growth (algae, lichen), and can enhance colour. It does not change the texture significantly if an impregnating sealer is used.

Types of sealer:

Application — Stone must be dry (at least 4 weeks after laying, in dry weather). Clean stone thoroughly first. Apply sealer with a lambswool applicator or brush; two coats with 30-minute interval between coats; wipe off excess immediately before it dries as a residue.

Frequently Asked Questions

Why is my Indian Sandstone going orange-brown?

Iron oxide staining from within the stone. High-iron sandstones (Kandla Grey, Autumn Brown) release iron when the stone first gets wet — the iron oxidises and stains the surface and any adjacent surfaces. Treatment: apply a proprietary iron stain remover (muriatic acid-based products — follow safety instructions carefully). Prevention: apply a penetrating sealer to the dry stone before wetting it for the first time.

Can I lay natural stone on a bed of sharp sand like block paving?

No. Natural stone flags must be laid on a mortar bed. Sharp sand (sand-only) bedding does not support the full underside of the stone, and any hollow area will flex and crack the stone under foot or vehicle loading. The mortar bed sets rigid and provides full support.

Should I use lime mortar or cement mortar for pointing?

For most residential natural stone paving, a 4:1 sand:cement mix is appropriate. Lime mortar (NHL 3.5 or NHL 5 + sharp sand, 1:3) is used in heritage/listed building contexts where the softer, self-healing properties of lime are required, and where cement pointing would be refused by planners. Lime pointing requires longer cure protection from rain and cold.

How long before vehicle use after laying natural stone?

Allow mortar bed and pointing to cure for minimum 7 days before any vehicle loading. 14 days in cold weather (below 10°C). Natural stone on full mortar bed cures to sufficient strength within 7 days under normal conditions.

Regulations & Standards