Sika SikaSwell S-2
A gun-applied, water-swelling polyurethane sealant that turns static construction joints and penetrations into a self-activating watertight barrier.
What is it?
A single-component, moisture-curing hydrophilic polyurethane sealant (oxide red) that expands on contact with water to seal non-moving construction joints and penetrations in concrete.
Where is it used?
Concrete construction joints, pipe and steel penetrations through walls and slabs, cable-duct entries, and as the adhesive that bonds SikaSwell A/P and Hydrotite CJ swellable profiles.
Why use it?
It self-seals: any water reaching the joint makes the sealant swell and press against the concrete faces, closing hairline gaps that a rigid sealant would leave open.
How is it applied?
Gun-applied from a 300 ml cartridge or 600 ml unipac as a continuous triangular bead onto a clean, sound, dry or matt-damp substrate, then left to skin and cure.
About Sika SikaSwell S-2
SikaSwell S-2 is Sika’s gun-grade member of the SikaSwell family, a one-component polyurethane that cures with atmospheric moisture and carries hydrophilic groups built into its polymer backbone. In service those groups draw in water and the cured bead swells, generating pressure against the surrounding concrete. That pressure is what does the sealing, so instead of relying on a permanent chemical bond alone, the joint is closed by controlled expansion whenever water is present. When the structure dries out the bead shrinks back toward its original size, and it swells again the next time water arrives, which is why it suits structures that see wet-dry cycling.
For engineers used to specifying rubber or PVC waterstops that must be cast into the pour, SikaSwell S-2 is attractive because it is applied after the first pour has hardened. A contractor can run a neat triangular bead along a cold joint, around a pipe sleeve, or through a cable duct, then place the second pour against it. That flexibility is also its main constraint: it is a sealant for static joints, not a movement-joint product, and it works only where concrete confines the swelling. Get the confinement and substrate right and it is one of the simplest ways to add a secondary water barrier to a below-grade structure.
The technical insight
The sealing mechanism is osmotic, not adhesive. Hydrophilic segments in the cured polyurethane attract and hold water molecules, and as water is absorbed the bead grows in volume; in demineralised water it swells roughly 25 percent in one day, about 100 percent by seven days and up to around 200 percent at thirty days. Because the concrete on either side stops the bead from expanding freely, that volume increase is converted into swelling pressure exceeding 10 bar in sound concrete, which clamps the sealant tightly into every surface irregularity of the joint and shuts off the seepage path. The confinement is essential: an unrestrained bead simply grows and generates little sealing force, which is why the product is rated against water pressures up to about 2 bar only when properly enclosed in the joint. Saline or mineral-rich water reduces the osmotic driving force, so swelling is slower and lower against groundwater than against fresh water, a factor worth allowing for in coastal and marine work.
Where it is used
- Sealing horizontal and vertical construction (cold) joints in in-situ concrete
- Sealing around pipe and steel penetrations through basement walls and floor slabs
- Waterproofing construction joints in cable ducts and service entries
- Bonding and adhering SikaSwell A and SikaSwell P swellable profiles to the concrete substrate
- Fixing Hydrotite CJ-type swellable strips into position before the second pour
- Secondary sealing at penetrations in water-retaining and below-grade structures
- Detailing complex junctions where a cast-in waterstop is impractical to place
Key advantages
- Self-activating: swells only where water is present and re-swells after drying, suiting wet-dry cycling
- Applied after the first pour hardens, so no need to fix a waterstop into wet concrete
- Gun-applied as a continuous bead that follows irregular profiles, pipe sleeves and tight corners easily
- Doubles as both a standalone joint sealant and the adhesive for SikaSwell swellable profiles
- One-component and moisture-curing, so no on-site mixing or ratio errors
- High swelling pressure (over 10 bar in sound concrete) drives a tight seal into surface irregularities
- Bonds to clean, matt-damp substrates, tolerating the not-quite-dry conditions common on site
Limitations & considerations
- Not suitable for movement or expansion joints; it is a static construction-joint sealant only
- Needs full concrete confinement to develop sealing pressure, so edge cover and joint geometry matter
- Rated for water pressure up to roughly 2 bar; higher heads call for a cast-in or combined system
- Swells slower and less in saline or mineral-rich water than in fresh water
- Must not be applied into joints holding standing water, and the substrate must be sound and clean
- Cures by moisture and has a limited placement window, so profiles must be set before the bead skins
Selection & best practice
Prepare the substrate first: it must be clean, sound and free of laitance, oil and loose material, and either dry or matt-damp with no standing water. Apply the sealant as a continuous triangular bead of adequate cross-section along the centre of the joint, keeping enough concrete cover on both sides so the swelling stays confined. Work within the application temperature range of +5 to +35 degrees C. The bead skins in about 60 minutes at +23 degrees C and 50 percent relative humidity, and where it is being used to bond a SikaSwell or Hydrotite profile, that profile should be pressed into place within roughly 30 minutes, before skin formation. Avoid burying the bead where it can swell without restraint. Allow the sealant to cure before the second pour is placed against it, and protect fresh beads from immediate water ingress until they have developed strength.
Specifications
| Product type | Single-component, moisture-curing hydrophilic polyurethane sealant |
| Colour | Oxide red |
| Density | Approx. 1.24 kg/l at +23 C |
| Swelling pressure | >10 bar in sound/ideal concrete |
| Swelling in demineralised water | ~25% at 1 day, ~100% at 7 days, up to ~200% at 30 days |
| Water pressure resistance | Up to approx. 2 bar (when confined in the joint) |
| Skin time | Approx. 60 minutes at +23 C / 50% r.h. |
| Application temperature | +5 C to +35 C |
| Pack sizes | 300 ml cartridge (12/box); 600 ml unipac (20/box) |
Industry use cases
Basements & below-grade structures
Sealing cold joints and pipe penetrations in retaining walls and raft slabs where groundwater pressure is present.
Water & wastewater
Secondary sealing of construction joints and penetrations in tanks, sumps and treatment structures subject to wet-dry cycling.
Metro & underground infrastructure
Detailing joints and service entries in cut-and-cover boxes and station structures where cast-in waterstops are hard to place.
Tunnels & ducts
Waterproofing cable-duct and service-duct construction joints, and bonding swellable profiles into position before pouring.
Podiums & wet areas
Sealing penetrations and cold joints in podium slabs, plant rooms and lift pits against nuisance water ingress.
Frequently asked questions
Can SikaSwell S-2 be used on movement or expansion joints?
How much water pressure can it hold back?
Do I apply it before or after the concrete is poured?
Will it still seal if the structure dries out?
Does it work as well against seawater as fresh water?
Can the substrate be damp when I apply it?
How we position Sika SikaSwell S-2
SikaSwell S-2 is the gun-applied sealant in Sika’s swellable range and pairs directly with the SikaSwell A and SikaSwell P profiles it is designed to bond, so a specifier can mix bead-and-profile details within one compatible system. Where a heavier or cast-in barrier is wanted, it complements Sika’s SikaWaterbar PVC waterstops and can back up membrane systems such as Sikaplan and SikaProof. As an authorised distributor across Delhi NCR and Pan-India, Space Arc also supplies equivalent swellable-joint solutions from other brands, including Fosroc’s Supercast SW swellable waterstops and Supercast SWX gun-applied paste, and Dr. Fixit and STP joint-sealing lines, so we can match the detail to the head of water, joint type and site preference rather than forcing a single product.
Fosroc Supercast SW20 — Choose the Fosroc Supercast SW20 swellable waterstop strip when the designer prefers a pre-formed, cast-in profile fixed into the joint rather than a gun-applied bead, particularly on long, regular construction joints.
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