What is a waterstop or waterbar?

A waterstop (or waterbar) is a pre-formed strip embedded into concrete joints — construction joints, expansion joints and kicker joints — to act as a physical barrier to water tracking through the joint. In UK practice the term waterbar is used interchangeably with waterstop, and both fall under Type B (structurally integral) protection in BS 8102:2022. There are three main families. PVC and rubber waterbars are dumbbell- or ribbed-profile strips cast half into each concrete pour, so water must travel around the full profile to cross the joint; they are robust but depend entirely on accurate placement before the pour. Hydrophilic waterstops are strips of bentonite or modified rubber fixed to the face of the first pour that swell up to several times their volume on contact with water, compressing against the fresh concrete to seal the joint; they are far easier to retrofit and are the usual choice for kickers and pile cap joints. Steel waterbars are used in heavy civil engineering where high water pressure or aggressive conditions rule out polymer products. Selection depends on the head of water, joint type and pour sequence — and a failed or missing waterbar in an existing structure is normally remedied from inside by resin injection or an injection hose system rather than by breaking out the joint.