What is a 'kicker' in concrete?

A kicker is a short concrete upstand — usually 50-100mm high, occasionally 150mm where a waterbar has to be housed — cast at the base of a wall or column, either monolithically with the slab or immediately after it. Its purpose is purely constructional: it gives the wall formwork a fixed edge to be clamped and aligned against, so the wall is cast in the correct position and the shutters cannot creep under the pressure of wet concrete. Without a kicker the formwork has to be located off setting-out lines alone, and line and plumb tolerances suffer. In UK practice kickers are set out to the National Structural Concrete Specification, with position typically held to within 10mm of the setting-out line and the top surface kept level so the wall shutter beds evenly. The problem with kickers is that they introduce a horizontal construction joint at the worst possible height — right at the base of the wall, where hydrostatic pressure in a basement or retaining structure is greatest. That joint is a cold joint: the kicker has set before the wall is poured against it, so the two pours never intermix, and it becomes the single most common leak path in below-ground concrete. Poor compaction in the narrow kicker zone, laitance left on the top surface, and honeycombing at the kicker toe all make it worse. Three details fix this. A hydrophilic waterstop can be fixed to the top of the kicker before the wall pour so it swells against the fresh concrete and seals the interface. An injection hose can be cast into the joint, allowing it to be grouted later if it leaks. On existing structures the usual remedy is a fillet seal at the kicker-to-slab junction combined with low-viscosity resin injection through the joint. Some contractors avoid the issue entirely with kickerless construction, using proprietary clamping systems that locate the shutter without a concrete upstand — though this shifts the tolerance problem onto the formwork rather than removing it. MPS Concrete Solutions seals leaking kicker joints in basements, car parks and retaining walls using resin injection and hydrophilic systems, working from inside the structure without excavation.