Movement joint

A flexible joint in tiling that lets the floor or wall expand and shrink without cracking or lifting the tiles.

Movement joints go where tiling meets walls and other materials, over joints in the building, and across large or heated areas. They're filled with a flexible sealant or a ready-made profile, not grout.

BS 5385 covers where they go. Leaving them out is a common cause of cracked and tented floors.