About Fosroc Hydrotite

Fosroc Hydrotite is a hydrophilic swellable waterstop engineered to stop water passing through the construction joints that are unavoidable in cast in-situ concrete. Unlike a conventional PVC waterbar that has to be cast centrally into fresh concrete and welded at every junction, Hydrotite is a slim rubber strip fixed to the face of the first pour and then buried by the second. When ground water or retained water eventually reaches the joint, the active hydrophilic component absorbs it and swells, filling the gap and pressing outward against the surrounding concrete to form a tight compression seal. Because it works by swelling rather than by mechanical geometry, it accommodates the small dimensional variations and surface imperfections that real site joints always have.

What makes the product distinctive is its co-extruded construction: a black, non-expanding chloroprene rubber section is fused to a blue hydrophilic rubber section in a single strip. The chloroprene gives the strip body and directs the swelling force across the joint rather than letting it dissipate, while the blue section does the sealing work. A factory-applied delay coating holds back expansion during the vulnerable period when green concrete is still curing or the joint may pond with rainwater, so the strip does not waste its swell before the structure is closed. Hydrotite is fully re-expandable — it shrinks back when a joint dries out and swells again on the next wetting cycle, which is why it suits structures that fill and empty repeatedly.

The technical insight

The sealing mechanism is osmotic, not mechanical. The hydrophilic rubber contains water-attracting polymers that draw moisture into the material and expand it in a controlled way — Fosroc rates the volume increase in the region of eight times (up to around 800%). That expansion is confined by the surrounding hardened concrete, so instead of simply growing, the strip develops internal pressure and squeezes into the joint like a gasket under load. The co-extruded black chloroprene backbone is the key detail: because it does not swell, it anchors the strip and channels the expansion force directionally across the joint, giving a far more reliable seal than an isotropic bentonite or single-material strip. The delay coating is equally important on Indian sites — monsoon ponding or a slow programme between pours would otherwise trigger premature swell, and a strip that has already expanded and dried before the concrete closes around it seals poorly. Provided a minimum of 100 mm of concrete cover is maintained, the developed swelling pressure is contained safely without cracking the surrounding section, and the joint can resist substantial hydrostatic head.

Where it is used

• Horizontal and vertical construction joints in basement rafts, retaining walls and wall-to-slab kickers
• Water and sewage treatment plant tanks, clarifiers and channels holding retained liquid
• Underground metro stations, box structures and cut-and-cover tunnel linings
• Reservoirs, water storage tanks and swimming pool shells
• Pipe and service penetrations passing through water-retaining concrete
• Construction pits, lift pits and sumps below the water table
• Joints between newly placed and existing concrete where little or no steel continuity exists
• Retro-fit sealing of joints in structures where a swellable strip can be adhered to a prepared face

Key advantages

• Swells automatically on water contact to form a self-energising compression seal without mechanical clamping
• Co-extruded design directs the expansion across the joint for a more dependable seal than single-material strips
• Delay coating prevents premature swelling while green concrete cures or the joint ponds with rainwater
• Fully re-expandable through repeated wet and dry cycles, ideal for tanks that fill and empty
• Self-adhesive (ADH) profiles fix straight to the concrete face, cutting installation time and adhesive cost
• No site welding, no special intersection pieces — corners and tees are made by simple butt joints
• Tolerates minor surface irregularities and small joint movement between new and existing pours
• Colour change from dark to light blue on swelling lets the site team visually confirm activation

Limitations & considerations

• Designed for low-movement construction joints, not for expansion joints or joints with significant cyclic movement
• Not recommended in suspended slabs or where excessive shrinkage or movement is expected
• Requires a minimum of 100 mm of concrete cover to contain swelling pressure without risk of cracking
• Must be protected from rain, ground water and ponding between pours or it will pre-expand and seal poorly
• Needs a clean, dry, sound first-pour face for reliable adhesion — rough or contaminated surfaces must be prepared first
• Expansion rate can vary in salt-laden or chemically contaminated water and should be checked for such exposures

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Hydrotite

Hydrotite is Fosroc’s premium co-extruded swellable waterstop and sits at the top of a graded family of joint-sealing options we stock. For a directly equivalent Fosroc alternative, Supercast SW20 is a 10 x 20 mm hydrophilic swellable strip that covers the same construction-joint duty at a keener price point, while Supercast SWX is the gun-grade swellable paste for sealing around pipe penetrations, rough faces and awkward details where a preformed strip is hard to run. Where the design instead calls for a cast-in central waterbar — typically expansion joints or heavy-movement joints that a swellable strip cannot serve — a Fosroc Supercast PVC waterbar is the correct choice. Across our other brands, teams standardising on a single supplier can consider comparable hydrophilic waterstops from Sika (the Hydrotite CJ range shares this exact technology) or from BASF/Master Builders Solutions. For complete below-ground packages we usually pair Hydrotite at the joints with a crystalline or membrane waterproofing system over the concrete faces; our team can specify the full build-up for basements, tanks and tunnels.

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