An expansion joint (also referred to as a movement joint) is a planned joint which is designed to allow two sections of concrete or masonry to expand and contract. This structural gap between adjacent parts of a structure allows for safe and inconsequential relative movement of those parts, which can be caused by thermal variations, creep (a phenomenon which causes a redistribution of stress away from points of intensity), shrinkage, ground settlement or other conditions. Expansion joints are incredibly useful when laying new concrete or reinforced concrete within an area bounded by walls or buildings, as they allow the concrete to expand and/or contract without transferring pressure onto other structures, which potentially could cause cracks within the concrete slab or the wall.

The key function of waterproofing an expansion joint is to minimize water ingress into a structure by creating a secure waterproofing barrier. Penetrating water may cause damage and may reduce the usage and lifecycle of the building.