outbond
Of a brick or stone: laid with its length parallel to the face of the wall.
outbond: brick laid lengthwise across the wall face
An outbond brick is one laid so that its length runs parallel to the face of a wall, rather than perpendicular to it. In a stretcher bond pattern, the most common masonry arrangement, outbond courses alternate with headers (bricks laid end-out) to tie the wall together. The outbond brick shows its long dimension on the exterior, giving the wall its characteristic running bond appearance.
The term reflects its function: the outbond brick spans across the wall face, while headers reach inward to bind the inner and outer wythes together. A standard UK brick is 215 mm long, 102 mm wide, and 65 mm high, so an outbond course displays the full 215 mm length. This creates a visual rhythm and, critically, ensures the wall acts as a monolithic structure rather than a collection of separate layers.
Bonding patterns and structural purpose
In Flemish bond, the traditional pattern for solid walls, outbond courses alternate with courses of mixed headers and stretchers. In English bond, full outbond courses alternate with full header courses. The outbond course alone provides no wall strength; the headers that follow penetrate the depth of the wall and lock it all together. Modern cavity walls often use outbond courses on both the outer leaf and inner leaf, with the cavity left empty or filled with insulation.
Mortar bed thickness affects the structural behavior of outbond courses. Thicker beds (above 12 mm) can accumulate differential settlement and reduce bond strength. The outbond brick must be laid with full mortar contact on all bed joints and head joints, or voids weaken the course and allow water penetration. Poor workmanship here, leaving hollow head joints or thin mortar, is a common source of damp problems.
The outbond course is vulnerable to spalling and frost damage on exposed elevations because water can pool on the horizontal surface. In cold climates or near the coast, the selection of brick type and mortar strength becomes critical; soft bricks or weak mortars will not survive repeated freeze-thaw cycles on outbond courses. Lime mortar is often preferred in heritage work because it allows movement and breathes, whereas modern cement mortars can trap moisture and accelerate brick deterioration.