What is an expansion joint? A small gap that prevents a big crack

An expansion joint is a gap deliberately left in building elements to absorb the stresses caused by temperature change, shrinkage and expansion, loading or settlement. Buildings move; if the movement has nowhere to go, it cracks its own way through.

Why it is needed

• Prevents cracking: takes up the movement of the structure and extends its life.
• Protects the building: keeps stresses under control so the frame and finishes are not damaged.
• Handles temperature: gives the structure room to expand and contract.

Types

• Structural joint: the main joint through the load-bearing system, separating building blocks.
• Architectural joint: left in the finishes for visual reasons while still taking up movement.
• Expansion joint: absorbs growth caused by heat.
• Shrinkage joint: controls the contraction of concrete as it cures.

Where you meet it

Between long building blocks, in wide screeds and tiled floors, on terraces and car park decks, in curtain walls and retaining walls.

Correct detailing

• The joint must run through every layer beneath the finish — a joint left only in the surface does nothing.
• Fill the gap with a compressible backer rod and seal it with a flexible sealant.
• Use a metal or PVC movement profile on exposed surfaces.
• On tiled floors joints are usually planned every 20–25 m².

Points to watch

• Never fill an expansion joint with rigid mortar.
• Waterproofing must continue across the joint with a flexible tape.
• Joint positions belong in the design from the start; a joint cut later reacts too late.