What Are Articulation Joints? Spacing, Placement and Sealing Explained
An articulation joint is a deliberate vertical gap built through a brick or block wall so the wall can move — with its footing, with temperature and with moisture — without cracking. It runs the full height of the wall, is usually 10 mm or wider, and is filled with flexible sealant over backer rod, never mortar. Get the spacing or the filling wrong and the wall makes its own joint: a crack.
Quick answer: space articulation joints no more than about 6 m apart in straight brickwork, and at no more than 5 m centres and within 1.2 m of any opening larger than 900 × 900 mm (NCC housing provisions). Width at least 10 mm. Required on reactive clay sites; generally not on class A or S sites. The engineer's detail and AS 3700 / AS 4773 govern — the figures here are the commonly applied rules, not a substitute for them.
Why brickwork needs articulation joints
Clay brick walls expand slowly for years as the bricks absorb moisture; concrete blocks shrink. Both move with temperature. And on Melbourne's reactive clay soils the footing itself rises and falls with the seasons — a few millimetres is routine, more in a dry year. Masonry is strong in compression and almost useless in tension, so when the footing rotates or the wall grows, something has to give. An articulation joint is where you choose for it to give. Without one, the wall chooses: usually a stepped crack through the mortar near a window, a door, or a change in wall height.
How far apart should articulation joints be?
The spacing that applies to your job comes from the structural drawings or the engineer's detail, and ultimately from AS 3700 (masonry structures) or AS 4773 (masonry in small buildings). The commonly applied rules behind those documents:
| Situation | Commonly applied rule |
|---|---|
| Straight wall, no openings | Joints at no more than about 6 m centres |
| Wall with openings larger than 900 × 900 mm | Joints at no more than 5 m centres, located within 1.2 m of the opening |
| Minimum joint width | 10 mm (wider for longer panels and higher-movement sealants) |
| Changes in wall height or footing depth | Joint at the change — these are where cracks start |
| Near external corners | Keep joints away from the corner by roughly the wall height, unless the detail says otherwise |
| Site classes A and S (stable) | Vertical articulation joints generally not required |
| Site classes M, H and E (reactive clay) | Required; spacing tightens as reactivity increases |
Two cautions. First, these are maxima — closer is always allowed and often wiser on long, low walls in full sun. Second, veneer walls still need wall ties either side of each joint (within about 300 mm), so a joint is a bricklaying detail as well as a sealing one.
Articulation joint vs control joint vs expansion joint
The terms get used loosely on site. They are all movement joints, but they do different jobs:
- Articulation joint — lets a masonry wall move with its footing and with the brick's own growth. Full-height, sealed flexible.
- Control joint — a planned line of weakness in concrete or blockwork that tells shrinkage where to crack. Often tooled or sawn, then sealed.
- Expansion joint — a full gap between two slabs or elements so they can grow towards each other without pushing. See our expansion and control joint sealing page and the joint width calculator.
What happens when articulation joints are missing, mortared or badly sealed
- Missing joints — stepped diagonal cracks from window and door corners, or straight vertical cracks every few metres. The wall has made its own joints.
- Mortared joints — a surprisingly common defect. Mortar is rigid, so the joint does nothing and the crack appears beside it. Cut out and re-seal.
- Hardened or failed sealant — old polyurethane that has gone brittle, split down the middle, or peeled off one face lets water in and stops the joint moving. Re-seal before the brick arrises start to spall.
- No backer rod — sealant bonded on three sides tears on the first hot summer. Every articulation joint needs closed-cell backer rod behind the sealant.
How articulation joints are sealed
- Confirm the joint is clear through the full wall thickness and the full height — no mortar bridges, no debris.
- Clean and, where the sealant data sheet requires it, prime the joint faces.
- Insert closed-cell backer rod sized larger than the joint, set to give a sealant depth of about half the joint width (minimum 6 mm).
- Gun in a flexible polyurethane or hybrid sealant with ±25% movement capability or better, colour-matched to the brick or mortar.
- Tool to a slightly concave finish so the bead is in full contact with both faces and sheds water.
Done properly, an external articulation joint seal lasts around 10–20 years before it needs renewing. If the joints on your building are cracking, peeling or were mortared solid, that is the work Gapless does every week — see brick and blockwork joint sealing, or book an inspection if you'd rather have the wall diagnosed first.
Last reviewed: October 2026. General guidance for Australian masonry; it does not replace AS 3700, AS 4773, the NCC or your engineer's detail. Gapless are caulking contractors, not engineers or certifiers.