Sika · crack injection

Sika SikaSwell A

Sika SikaSwell A is a hydrophilic, single-component, polyurethane-based swelling waterstop profile for the watertight sealing of construction joints, penetrations and discontinuities in concrete substrates. The profile is supplied as a continuous extruded strip, typically 20 mm × 5 mm or 20 mm × 10 mm cross-section, in coils of 5 m to 20 m length. SikaSwell A is bonded to the substrate by SikaSwell S-2 polyurethane adhesive and incorporated into the construction joint or sealed against the penetration before the second concrete pour or before the joint is closed. On contact with water, the SikaSwell A profile swells to approximately 200% of its installed cross-section over 24-72 hours, producing a self-sealing pressure against the surrounding concrete that prevents water passage through the joint. The swelling action is permanent and reversible — the profile can swell, dry and re-swell repeatedly over the design life of the asset. TRSC specifies SikaSwell A on remediation projects where a new construction joint is being formed at a repair-to-existing interface (typical of section enlargement, slab-edge replacement, and basement-wall repair) and the engineering intent is permanent watertight sealing without the labour cost of a metal or PVC waterstop installation.

Manufacturer Datasheet
TRSC Specifier Commentary

SikaSwell A is TRSC's default hydrophilic waterstop specification on remediation projects where a new construction joint is being formed at a repair-to-existing interface and the engineering intent is permanent watertight sealing. The product is selected over alternative waterstop systems (PVC waterstop, hydrophilic bentonite waterstop, swelling rubber waterstop) on three grounds: it can be retrofitted onto existing concrete by adhesive bonding (no requirement to embed in the first pour, which is essential for repair-to-existing joints); it has the highest documented swelling capacity in the polyurethane swelling-waterstop category (~200% expansion); and the swelling action is reversible across multiple wet-dry cycles, which is the appropriate specification for joints exposed to fluctuating groundwater. The most common specification pitfalls TRSC encounters in the field are: (1) premature wetting — SikaSwell A swells on contact with any water, including condensation, rain on the exposed substrate during installation, and pour-water from the second concrete placement; if the profile swells before it is fully encapsulated by the second pour, the encapsulation traps the swollen profile in a swollen state with no remaining swelling capacity for in-service water; the profile must be installed dry, the second pour must be placed within 24 hours of installation, and the substrate must be dry at installation; (2) confinement — SikaSwell A develops its sealing pressure by swelling against the surrounding concrete; the profile must be confined on all four sides by the concrete pour or by the existing substrate, with no escape path for the swelling action; field installations that fail to confine one face produce a profile that swells out of the joint rather than sealing it; (3) adhesive selection — only Sika SikaSwell S-2 polyurethane adhesive is approved for bonding the profile to the substrate; substituting a generic construction adhesive (silicone, PU, MS polymer) compromises the bond and the profile shifts position during the second pour. TRSC specifications cite the adhesive product, the installation timing constraints, and a witness hold point at the end of each waterstop installation phase before the second pour is cast.

Frequently Asked Questions

Specification questions about Sika SikaSwell A

When is a hydrophilic waterstop the appropriate specification?
Hydrophilic waterstops (such as SikaSwell A) are appropriate where a new construction joint is being formed at a repair-to-existing interface and the engineering intent is permanent watertight sealing without the labour cost of a metal or PVC waterstop installation. They are particularly suited to repair work because they can be retrofitted onto existing concrete by adhesive bonding rather than requiring embedment in the first pour. They are not appropriate for joints subject to dynamic movement (use a flexible elastomeric waterstop) or for joints with insufficient confinement (which require traditional waterstop systems).
Why must the waterstop be installed dry?
SikaSwell A swells on contact with any water, including condensation, rain, and pour-water from the second concrete placement. If the profile swells before it is fully encapsulated by the second pour, the encapsulation traps the swollen profile in a swollen state with no remaining swelling capacity for in-service water. The profile must be installed dry, on a dry substrate, with the second pour placed within 24 hours of installation. TRSC specifications cite installation timing constraints and a witness hold point.
What pressure can SikaSwell A seal against?
When properly installed and confined, SikaSwell A can seal against hydrostatic pressure up to approximately 5 bar (50 m water head). The achievable sealing pressure depends on the cross-section selected, the confinement quality, and the substrate condition; for high-pressure applications the larger cross-section variants (25 × 20 mm) are specified. TRSC remediation specifications cite the cross-section by application context.
Is the swelling reversible?
Yes. The polyurethane swelling action is reversible across multiple wet-dry cycles, which is the appropriate specification for joints exposed to fluctuating groundwater. The profile swells when wet, contracts when dry (over weeks rather than days), and re-swells on next wetting cycle. The published service life is the structural life of the surrounding concrete, typically 50+ years.
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Relevant Services
Remediation Design
Structural Investigation
Sources & Further Reading