Turf Cutting Agronomy & Herringbone Masonry: Strengur Strips, Hnaus Blocks, Root-Felt Density, and Wall Compaction

The mechanical integrity of an un-mortared turf wall does not come from the soil itself, but from the microscopic biological network of living plant roots. Traditional turf cutters (torfmenn) strictly avoided dry hillside grasslands, which contain loose volcanic tephra ash and shallow, sparse grass roots that crumble when handled.

Construction turf was harvested exclusively from waterlogged sedge bogs (flói and mýri). In these anaerobic wetland soils, common sedge (Carex nigra), bottle sedge (Carex rostrata), and alpine cotton grass produce dense, fibrous rhizome mats extending 30 to 50 cm below the surface. The high tensile strength of the living sedge roots functions exactly like steel rebar in reinforced concrete: resisting tensile bending forces, preventing water erosion, and allowing long ribbons of turf to be rolled, transported on pack horses, and bent around wall corners without fracturing.

Harvesting turf required specialized forged iron tools developed over centuries. The primary tool for cutting turf ribbons was the torf-ljár (turf scythe or crescent spade)—a long wooden shaft fitted with a broad, curved, razor-sharp iron blade set at a right angle to the handle.

To cut strengur, the cutter walks backward across the bog, slicing through the root carpet in continuous parallel grooves spaced 18 cm apart. A second craftsman using a flat spade (reka) slices horizontally beneath the roots at a calibrated depth of 5 cm, peeling up continuous sod ribbons up to two meters long. For thick load-bearing blocks—klömbruhnaus—a heavy rectangular turf spade (torf-skófla) is driven vertically into the earth, cutting blocks with a trapezoidal profile: a thick, square outer face that forms the exterior wall surface and an elongated, tapering tail that anchors deep into the interior core of the wall.

Laying a turf wall is an exercise in gravity compaction and geometric interlocking. Traditional turf walls are built with a distinct double-skin construction: an exterior face of patterned turf, an interior face of flat turf blocks, and a central core of loose peat earth and gravel.

On the exterior face, the master mason lays strengur strips in fiskislóð (herringbone or fish-bone pattern). One course is laid with strips sloping 45 degrees downward from left to right; the subsequent course is laid sloping 45 degrees downward from right to left, separated by a single flat horizontal leveling layer (strenglag). This herringbone geometry provides two vital advantages: (1) it eliminates continuous horizontal and vertical joint seams where driving rain can penetrate; and (2) as the wall naturally settles by 15% to 20% over its first two years, the angled blocks wedge tightly against one another, locking the wall under increasing compression. Every two courses, the central core is tamped firmly with heavy wooden rammers (drepill), creating an airtight, draft-free thermal barrier.