What is the horizontal layer of mortar on which a masonry unit is laid called?

The term used for the horizontal layer of mortar on which a masonry unit is laid is known as a bed joint. This layer provides a level and stable surface for the masonry units, ensuring proper alignment and support for the units stacked above it. Bed joints also play a critical role in the overall strength and stability of a masonry wall, as they help distribute the weight of the units evenly.

When laying brick or block, the thickness of the bed joint can impact the appearance and structural integrity of the wall. A well-formed bed joint can also facilitate better bonding between the masonry units and the mortar, enhancing the durability of the structure.

While other terms like header joint or mortar joint refer to different aspects or configurations of masonry construction, they do not specifically denote the horizontal layer upon which the units are placed. Understanding this terminology is fundamental for anyone working in masonry, as it helps in discussing techniques, methods, and structural considerations in the field.