Question 1

What is a waterstop or waterbar?

Accepted Answer

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. In more detail, the distinction that matters on site is where the strip sits relative to the pour. A cast-in PVC or rubber waterbar has to be positioned, supported and fixed so that it stays central as the concrete is placed and vibrated around it; if it folds over, gets pushed to one side, or is left with a void beneath the lower flange, the joint will leak along the face of the strip itself and the defect is buried in the concrete where nobody can see it. Joints in the strip have to be welded or vulcanised, not overlapped, and the junctions — tees, crosses and corners — are the most common failure point, which is why factory-made junction pieces are preferred over site-formed ones. A surface-fixed hydrophilic strip avoids all of that because it is simply nailed or glued to the top of the kicker or the face of the first pour before the second pour goes against it, but it has its own constraint: it must be kept dry until the concrete is placed. A hydrophilic strip that is rained on, or left in a flooded excavation over a weekend, swells early, loses the expansion capacity it was relied on for, and can even spall the young concrete around it as it expands against restraint. Products with a delayed-swell coating exist for exactly that reason. Injection hose is the third option, and increasingly the default where a joint is critical: a perforated hose is cast into the joint with its ends brought out to accessible ports, and it is left alone unless the joint leaks — at which point resin or microfine grout is injected through it to seal the interface without any breaking out. It is the only one of these details that is maintainable after the structure is finished, and in a basement or water-retaining structure it is usually specified alongside a waterbar rather than instead of one, as part of the combined protection approach BS 8102:2022 encourages. On an existing structure the practical question is rarely which waterbar to use but what to do without one. Breaking out a construction joint to retrofit a cast-in strip is destructive, expensive and risks the reinforcement, so the normal remedy is to inject the joint: polyurethane resin where water is actively running, which reacts with the water itself and foams to fill the path, or an acrylic or microfine cement grout where the joint is damp and a more permanent, lower-viscosity fill is wanted. A fillet seal and a bonded surface system are often added on the inside face afterwards so the repair does not depend on the injection alone. MPS Concrete Solutions seals leaking construction and kicker joints by resin injection and hydrophilic systems in basements, car parks, lift pits and retaining walls, working from inside the structure without excavation.

Question 2

What is an injection hose system?

Accepted Answer

An injection hose is a perforated tube installed in concrete construction joints before the concrete is poured. If a leak occurs later, resin can be injected through the hose from accessible entry points, traveling along the joint and sealing it from within. It is a 'maintainable' detail often required by BS 8102:2022 for Type B structures, providing a backup plan for joint failure without the need for destructive drilling.

Question 3

What is a 'kicker' in concrete?

Accepted Answer

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.

Question 4

What is Type A waterproofing?

Accepted Answer

Type A waterproofing, often called 'Barrier Protection,' involves applying a waterproof material to the internal or external surfaces of the structure. This blocks water ingress physically. Examples include external adhesive membranes applied before backfilling (positive side) or internal multi-coat rendering/tanking slurries (negative side). While effective, Type A relies 100% on the workmanship and substrate preparation; a single defect can lead to failure, which is why we often combine it with other systems.

Question 5

What is Type B waterproofing?

Accepted Answer

Type B waterproofing is 'Structurally Integral Protection.' It relies on the design and materials of the structure itself to be water-resistant. This is typically achieved using waterproof concrete (containing hydrophobic admixtures) and waterstops embedded in the construction joints (like hydrophilic strips or metal waterbars). While the concrete itself blocks water, the joints are the weak points, which is why MPS specializes in injection hose systems to seal these joints post-construction if needed.

What is a waterstop or waterbar?