What is a Perpend (Cross) Joint?
A perpend joint (also called a cross joint or head joint) is the vertical joint between two bricks placed side by side in masonry. Together with the horizontal bed joint, the perpend joint forms the joint pattern visible in every piece of masonry. A well-filled perpend joint is essential for the weathertightness and strength of a wall.
Perpend Joint vs. Bed Joint
| Perpend joint | Bed joint | |
|---|---|---|
| Direction | Vertical | Horizontal |
| Width | 10 mm (standard) | 10–15 mm (standard) |
| Role | Weathertightness, expansion | Load-bearing capacity, stiffness |
Open Perpend Joint — What is That?
An open perpend joint is a vertical joint that is deliberately not filled with mortar. This is done in the bottom course of a cavity wall or facade cladding so that condensation running down through the cavity can escape to the outside.
An open perpend joint is therefore part of moisture management in a cavity wall — not a mistake, but a deliberate detail.
Not Aligning Perpend Joints (Bond)
In good masonry bond the perpend joints in successive courses never fall directly above each other. They are staggered by half 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
Repointing Joints
When joints weather, they can be repointed:
- Rake out old mortar to 2–3 cm depth
- Remove dust and loose debris, dampen the wall
- Press joint mortar in with a pointing key
- Profile the joint: bucket-handle (concave), flush or recessed
Related Terms
- Masonry bond
- Mortar
- Mortar mix
- Cavity wall
- Soldier course
- Bed joint
More guides and plans available at fredsdiyplans.com