What is a movement joint in a building?

A movement joint is a deliberate, continuous break designed into a building or concrete structure that allows the sections either side to expand, contract, deflect or settle independently without cracking each other. The term covers several types: expansion joints (which accommodate thermal expansion), contraction joints (which control where drying shrinkage cracks form), isolation joints (which separate a slab from columns or walls), and seismic or settlement joints in larger structures. Movement joints are needed because concrete moves constantly — it shrinks as it dries, expands and contracts with temperature, and deflects under load; without planned joints, that movement finds relief by cracking the structure at random. A movement joint is filled with a compressible filler board and sealed at the surface with a flexible sealant over a backer rod; in trafficked areas like car park decks, a mechanical joint system with metal edge rails is used instead. It is the surface seal that fails — typically every 10-15 years — and a failed joint seal is one of the most common sources of water damage in car parks, podium decks and basements. Resealing a movement joint costs roughly £25-£60 per linear metre, rising to £80-£200 where the joint edges have spalled and need rebuilding first.