Dry Stone Wall Building Techniques

Why Dry Stone Handles Frost Better Than Mortar

In Canada, ground movement from freeze-thaw cycling is one of the primary causes of wall failure. A mortared wall is a rigid structure: when frost heaves a section, the mortar cracks, and water enters the crack, accelerating deterioration. A dry stone wall has no mortar joints to crack. Individual stones can shift slightly under frost pressure and settle back, distributing movement rather than concentrating it in failure points.

The Dry Stone Walling Association documents this property in its technical guidance and is a recognized authority on the subject. Their published certification standards describe the structural principles that underpin the method described here.

Planning the Wall

Before placing a single stone, the following decisions need to be made:

• Type: Freestanding (two faces visible) or retaining (one face against soil or a slope)?
• Height: A freestanding dry stone wall is typically 900 mm to 1,200 mm tall. Beyond that, professional assessment is advisable for load calculations.
• Base width: For a freestanding wall, base width should be roughly half the finished height. A 900 mm wall needs a base of about 450 mm. Retaining walls need additional base width on the soil side.
• Stone volume: A rough estimate: for every metre of finished wall face area, expect to use approximately 1.5 to 2 times that volume in raw stone, accounting for sorting and waste.

Preparing the Base

Excavate a trench to a depth of at least 150 mm below grade — 200 mm is preferable in areas with heavy frost. The trench width should match the planned base width of the wall. Fill with compacted crushed stone or gravel (clear stone, not stone dust) to within 50 mm of grade. This provides drainage beneath the wall and reduces frost uplift.

Do not lay directly on topsoil. Topsoil compresses unevenly and retains moisture against the base course stones, accelerating deterioration and causing settlement.

Selecting and Sorting Stones

Before building begins, sort the stone pile into rough categories:

• Foundation stones: The largest, heaviest, flattest-based stones available. These go in first.
• Face stones: Stones with at least one flat or roughly flat face, to present toward the wall exterior.
• Bonders (through-stones): Stones long enough to span most of the wall's width. These tie the two faces together structurally. A wall should have bonders every 600–900 mm of height and every 1–1.5 m of length.
• Hearting: Smaller stones and rubble used to fill the interior space between the two faces.
• Capping stones: Flat or wedge-shaped stones laid on the top course to shed water. In freestanding walls, these are often the most visible elements and should be selected for consistent size.

Building in Courses

The basic rule is: one stone over two, two stones over one. Every vertical joint in one course should be covered by a stone in the course above. Running joints — vertical gaps aligned across multiple courses — create planes of weakness that frost can exploit.

1. First course: Place the largest foundation stones on the compacted gravel bed, flat side down, flat face outward. Fill gaps between them with hearting. Stones in this course should be stable with no rocking.
2. Build both faces simultaneously: Work along both faces of the wall in short sections rather than building one face to full height first. This keeps the structure balanced.
3. Batter: Dry stone walls lean inward slightly from base to top — this is called batter. A typical batter is 25 mm of inward lean for every 300 mm of height (roughly 1:12). A wooden batter frame (a trapezoid-shaped guide held against the wall face) makes maintaining consistent batter easier.
4. Place bonders: Insert through-stones at each appropriate course, running them from face to face or as close to the opposite face as possible.
5. Pack hearting: After each course, fill the interior tightly with hearting stone. Pack it firmly — the hearting carries load and prevents face stones from moving inward.
6. Cap: Set capping stones on edge (on their narrow side, like books on a shelf) or flat, depending on stone shape. Cap stones should overlap each other and be packed tight to prevent dislodging.

Common Mistakes

• Using round stones as face stones — they are better used as hearting or base fill.
• Building only one face to height before the other — creates an unstable leaning structure during construction.
• Skipping or inadequately spaced bonders — the two faces can separate over time.
• Too little hearting — face stones have no backing support and shift under load.
• Laying on a flat ground surface without a compacted base — settlement will be uneven.

Maintenance Over Time

Dry stone walls require periodic inspection. After winter, check for sections where stones have been displaced by frost. Reset displaced face stones promptly — a small gap in a course allows water to enter and freeze, widening the gap over successive winters. Vegetation growing in wall joints should be removed while young; mature woody roots can split courses apart.

Last reviewed: May 2026. References: Dry Stone Walling Association (dswa.org.uk), National Research Council Canada.