heartbond
A bond in a stone wall in which two headers meet in the middle of a wall and another header covers the joint between them.
heartbond: two headers meeting at the center line
A heartbond is a masonry pattern used in cavity walls and thick stone construction where two headers meet end-to-end at the centerline of the wall, with a third header placed directly above or below to cover the vertical joint between them. This arrangement ensures that the joint between the two center headers does not run through to the face of the wall, maintaining structural integrity and weather resistance across the full thickness.
The term describes a specific geometry in Flemish bond, English bond, and other traditional bonding patterns. In a typical course, you might see a stretcher face followed by a header that runs the full depth, then the two heartbond headers at center, then another full header, and stretchers to close the course. The covering header sits in the perpends (mortar joints) of the two headers below, preventing water and structural weakness from a continuous vertical crack.
Heartbond becomes critical in walls thicker than about 450 mm or in rubble stone masonry where the builder cannot rely on uniform units. In single-leaf stone walls built without a cavity, the heartbond pattern ensures the center of the wall is properly locked. In two-leaf cavity construction, heartbond may be used in either leaf or reserved for the outer leaf where appearance and durability matter most.
The pattern requires careful material selection and layout. Stones or bricks suited to heartbond must be long enough to span from one face nearly to the center, and the covering header must sit firmly in the mortar bed without bridging the lower joint. Poorly executed heartbond, where the covering header rocks on two points rather than bedding fully, creates a weak spot prone to cracking and water ingress during freeze-thaw cycles.
The name reflects the literal function: the heart of the wall, its center, is bonded solidly rather than left as a joint line. In modern construction with hollow concrete blocks and cavity ties, heartbond has become less common, though the principle remains relevant in conservation work, stone restoration, and thick masonry where traditional methods are specified or required.