Bed joint | Chalkline

A bed joint is the horizontal mortar joint laid between each course of bricks or blocks. The bed transfers vertical load between courses, bonds the units together, and provides the weatherproof seal at the bed line. Standard nominal thickness on residential brickwork is 10 mm, allowing the trade to lay courses to gauge (3 courses + 3 beds = 230 mm gauge for standard 76 mm bricks).

The full-bed rule. A bed joint must be fully filled across the full brick width. Two reasons:

Structural performance: brickwork is designed in AS 3700 on the assumption of a full bed. Partial beds reduce the loaded contact area and cut the wall’s compressive and shear strength.
Weatherproofing: a partial bed creates a void inside the wall that admits wind-driven rain through perpends and bed gaps.

Furrowing (a finger-pushed groove down the centre of the bed) is sometimes used to manage initial bedding suction so the brick sits to gauge without rocking. Furrowing is only acceptable if the bed is fully filled across the full width before furrowing, with the furrow being a depression in the bed rather than a gap. A furrow that exposes the unit below is a defect.

Common bed defects:

Snicked beds: the brickie deliberately laid a thin or partial bed to save mortar or correct a height error. Visible as a thin line on raking.
Hollow beds under face brick on cavity walls: the inner edge of the bed is fully laid but the outer edge is starved. Tap-test by tapping each brick during build; hollow returns dull sound.
Bed thickness variation: courses laid at 8 mm one course and 14 mm the next. Visible to a sharp eye; flagged in PCI inspection.
Mortar dropped on inner cavity face: drops onto cavity ties and creates moisture bridges. Cavity should be kept clean during the lay.

Specialised bed-joint conditions:

Below DPC: bed joints must use an exposure-grade-compatible mortar mix (typically M3 mortar per AS 3700) to resist salt attack and dampness.
Reinforced bedded brickwork uses bed-joint reinforcement (Brickforce, Bekaert) every 2 to 4 courses to control shrinkage cracking on long walls.
Articulation joints: vertical full-width gaps in masonry walls; bed joints either side are tooled normally.
Slip joints at slab edges or beam supports: the bed is replaced with a flexible slip layer (membrane, neoprene, or sliding plate) to accommodate differential movement.

For builders. Walk the brickwork at completion of each lift:

Raked-joint walls: visually check every bed for full coverage and consistent depth.
Struck-joint walls: tap-test brick faces; hollow returns mean a starved bed.
Check gauge with a 4-course block (4 bricks + 4 beds should hit nominal gauge ±2 mm).

Also known as: bed, bedding joint, horizontal mortar joint.

Category: Practical / masonry / mortar joints.

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