What is a perpend?
A perpend (also called a perp joint) is the vertical mortar joint between two bricks laid side by side in a course of masonry. Together with the horizontal bed joint, the perpend creates the joint pattern visible in all brickwork. A well-filled perpend is essential for the watertightness and strength of a wall.
Perpend vs. bed joint
| Perpend | Bed joint | |
|---|---|---|
| Direction | Vertical | Horizontal |
| Width | 10 mm (standard) | 10-15 mm (standard) |
| Role | Watertightness, movement | Load-bearing capacity, rigidity |
Open perpend — what is that?
An open perpend is a vertical joint that is deliberately not filled with mortar. This is done in the bottom course of a cavity wall or cladding so that condensation water running down the cavity can escape to the outside.
An open perpend is therefore part of moisture management in a cavity wall — not a mistake, but an intentional detail.
Not aligning perpends (bonding)
In good masonry bonding, perpends in consecutive courses never fall directly above one another. They are staggered by half a brick or a quarter brick. This provides:
- Better load distribution — the load travels in a zigzag through the masonry
- Higher tensile strength — bricks effectively interlock with each other
- Aesthetic pattern — the recognisable appearance of brickwork
Re-pointing
When joints weather and deteriorate, they can be re-pointed:
- Rake out the old mortar to a depth of 2-3 cm
- Remove dust and loose debris, dampen the wall
- Press pointing mortar in with a pointing tool
- Profile the joint: hollow, flush or recessed
Related terms
- Masonry bond
- Mortar
- Pointing mortar
- Cavity wall
- Soldier course
- Bed joint