The visible surface of a cobblestone path represents only the top layer of a construction system that goes 30–50 cm below ground. How that system is built determines whether the surface remains stable over multiple winters or develops settlement, rocking stones, and weed growth within a few seasons.

Understanding the Layer System

A traditional cobblestone installation consists of three layers below the stone itself: a compacted subgrade (the natural ground), a sub-base of crushed aggregate, and a bedding layer on which the stone is set. Each layer has a different function and a different specification depending on the load the surface will carry.

Subgrade preparation

The starting point is the natural ground. Topsoil contains organic material that compresses under load and supports plant growth — both of which cause long-term movement in paving. The standard approach is to excavate and remove all topsoil from the project area, plus additional depth to accommodate the construction layers. Typical total excavation depth for a pedestrian garden path is 30–35 cm; for a driveway, 45–55 cm.

After excavation, the exposed subgrade is compacted with a plate compactor. Clay subgrades in particular can lose bearing capacity when wet, and additional drainage or stabilisation may be needed before building up the layers above.

Sub-base

The sub-base is typically crushed aggregate — in Poland, commonly crushed granite or limestone graded at 0–31.5 mm or 0–63 mm. It is spread in layers of no more than 20 cm each and compacted before the next layer is added. The sub-base distributes load from the surface down to the subgrade, and its thickness depends on what the surface will carry.

For a pedestrian garden path, a 15–20 cm compacted sub-base is generally adequate. For a driveway where a family car will park, 25–30 cm is more typical. Commercial vehicle access requires a structural calculation that goes beyond standard residential guidance.

A well-compacted sub-base is the primary defence against surface settlement. Under-specification here is the most common reason cobblestone paths develop hollows and rocking stones within a few years of installation.

Bedding Layer Options

The bedding layer sits directly below the stone and serves two purposes: it provides a level working surface for precise stone placement, and it accommodates the small dimensional variations between individual cobbles. There are two main approaches.

Sand bedding (dry laying)

A 3–5 cm layer of coarse sand (0–4 mm or 0–8 mm) is screeded flat and the cobblestones are set directly into it. This is the traditional method for sett paving and remains the most common approach for residential garden work. The surface can be disassembled and relaid if services need to be accessed below, which is a practical advantage.

Sand bedding allows slight movement during freeze-thaw, which means individual stones rarely crack from frost. However, fine particles can wash out of joints in exposed or sloped areas if not managed properly.

Mortar bedding (wet laying)

A semi-dry cement-sand mortar mix (typically 1:4 cement to sharp sand by volume) is used as the bedding layer. Stones are set into it and the mortar cures around the base of each sett. This gives a more rigid result and is preferred for sloped surfaces, areas with edge constraints, and vehicle areas where stone movement needs to be minimised.

The trade-off is that mortar-bedded surfaces are harder to dismantle. Frost movement is also less forgiving in rigid systems — if the sub-base is not properly compacted, cracking can propagate through the mortar rather than being absorbed.

Stone Setting

For sett paving, stones are placed with their longest dimension vertical — the stone is set into the bedding layer with only its top face exposed. This uses more material per square metre but produces a surface where the load is transferred down through the full depth of the stone. Flat-laid cobbles (long dimension horizontal) use less depth but have less structural integrity under point loads.

Joint width between setts affects both appearance and drainage. For 10×10 cm granite setts, joints of 3–5 mm are typical when a tight, regular pattern is intended. Wider joints of 8–15 mm allow for variation in stone size and give a more informal appearance.

Granite sett paving close-up

Granite sett paving showing joint width and surface texture. Source: Wikimedia Commons (CC BY-SA 2.0).

Joint Filling

After the stones are set and any necessary adjustments made, the joints between them are filled. The appropriate joint fill depends on the bedding system used.

Kiln-dried sand

For sand-bedded surfaces, kiln-dried sand is brushed across the surface and into the joints, then compacted with a plate compactor (with a rubber or foam pad to protect the stone surface). This is repeated until joints are fully filled. The surface can be used within hours.

Jointing mortar

Polymer-modified jointing mortars are available for semi-permeable jointing — they allow water movement but resist weed growth and are more resistant to wash-out than sand. These are applied as a slurry brushed into joints, then cleaned from stone surfaces before curing. They are slower to apply but more durable than plain sand in exposed positions.

Cement grout

For mortar-bedded installations, a cement-based grout mixed to a paste consistency is worked into joints and tooled flat. This creates a rigid, impermeable joint line. It is durable but cannot absorb movement — hairline cracking is possible in areas with significant temperature variation.

Edge Restraints

Without a solid edge, sett paving will migrate laterally over time, particularly in sand-bedded systems. Edge restraints can be formed with:

  • Kerb stones (granite or concrete) set in concrete haunching
  • Metal edge restraint profiles, pinned into the sub-base
  • A row of setts set in mortar around the perimeter
  • Existing structures (walls, foundations, borders) where they provide a firm edge

For garden paths bordered by planted areas, a defined edging also prevents grass and plant roots from encroaching under the paving layer.

Drainage Considerations

Permeable paving (sand joints, open gradation sub-base) allows rainwater to drain through the surface. This reduces runoff and helps manage surface water on flat or mildly sloped areas. For this to work effectively, the sub-base must remain permeable — fine particles from adjacent soil can migrate into it over time and reduce its permeability.

On sloped sites, or where the surface leads towards a building, cross-falls of 1–2% towards an edge drain or channel are incorporated to direct surface water away from structures.

For information on material choice before beginning installation, see Choosing Natural Stone for Outdoor Paving. For pattern and layout planning, see Driveway and Path Design with Granite Setts.