Temperature and moisture movement in long cavity walls causes cracks if the masonry cannot work. Vertical movement joints absorb the movement. Here is why brick expands and concrete shrinks, where joints are placed, and how they are formed with sliding ties and elastic joint sealant.
Introduction
Masonry is not rigid — it moves with temperature and moisture. A long, unbroken facade that cannot move cracks randomly, typically from corners and window corners. A vertical movement joint is a planned, vertical cut through the outer leaf that gives the masonry room to expand and contract without cracking uncontrolled. The distance is determined by calculation or by Mur & Tag's guideline distances — and an overlooked movement joint is a common cause of crack damage in facing walls.
Two opposite movements: tile expands, concrete shrinks
Clay bricks leave the kiln bone dry and then slowly absorb moisture from the air. This causes an irreversible moisture expansion — the stone grows slightly over the years — on top of the reversible movement from temperature and moisture. Calcium silicate bricks, concrete and lightweight concrete do the opposite: they shrink as they set and dry out. Therefore, a clay outer leaf and a concrete backing are often moving in opposite directions, and the permitted joint spacing depends on the masonry material.
How large can the joint spacing be?
The distance between vertical movement joints can be determined by calculation. If it is not, the Mur & Tag guidance gives guideline distances that depend on the normalised compressive strength f_b of the masonry unit and on the mortar. The distances apply to plinth solutions on felt, and the shortest distances are used when laying with strong mortars.
| Building stone | Distance between movement joints |
|---|---|
| f_b at least 15 MPa | 10–20 m |
| f_b at least 20 MPa | 15–30 m |
| f_b between 15 and 20 MPa | interpolated — do not extrapolate above 20 MPa |
- 01Slip layer (e.g. foil or steel sheet) across the full cross-section of the outer leaf: the distance can be increased by 20 %.
- 02Brackets that can follow a horizontal movement: the distance can be increased by 30 % (cannot be combined with a slip layer).
- 03Reinforced masonry (at least 0.05 % of the effective cross-section, reinforcement at least in every 6th course/400 mm): the distance can be increased by 30 %.
- 04The distance between movement joints or tie-free corners may be at most 30 m — except with very weak mortars (K100/1200), where in practice there is no maximum limit.
Where joints are placed
- 01At long, unbroken facade sections — with the standard's maximum mutual distance.
- 02At in- and outgoing corners, where two facades pull in each direction.
- 03At jumps in wall height or wall thickness.
- 04At large openings and close to window/door corners where the masonry is weakened and cracks start.
- 05Where the outer wall and inner wall of different materials meet.
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