Expanding resin for slab lifting, void filling, and ground strengthening — same-day trafficable.
Polyurethane grouting uses expanding two-component resin systems injected through small-diameter ports to fill voids, lift settled structures, strengthen weak ground, and seal water ingress — without excavation, without major disruption, and in most cases with same-day return to service. It is one of the most versatile and minimally disruptive ground treatment tools available, and GSI NZ operates purpose-built resin injection equipment with experienced crews who have delivered polyurethane grouting programmes across New Zealand.
The core application is slab lifting and void filling beneath concrete slabs, pavements, and infrastructure that has settled due to void formation, soil erosion, or loss of sub-base support. Resin is injected through small holes (typically 12–16mm diameter) drilled through the slab at a regular port pattern. As the resin expands, it fills the void beneath the slab and applies a controlled lifting force, re-levelling the structure with millimetre precision. The same-day cure means traffic and operational loading can resume within hours of completion, making polyurethane grouting well suited to roads, warehouse floors, airport aprons, and other infrastructure that cannot sustain extended closures.
Beyond slab lifting, polyurethane grouting is used for ground strengthening beneath foundations where soil has been weakened by moisture, piping, or biological activity. Expanding resin permeates into the weak zone, encapsulating soil particles and increasing the bearing capacity of the ground without the need for excavation or underpinning. GSI NZ has used this technique to strengthen ground beneath operational buildings, industrial floors, and infrastructure foundations across New Zealand.
Polyurethane grouting is also effective for sealing active water infiltration — stopping leaks in joints, cracks, and interfaces in concrete structures including retaining walls, culverts, tunnels, and basement slabs. Hydrophilic resin systems react with water to form a flexible, watertight seal, making them the preferred solution where conventional cementitious grouting cannot achieve a reliable seal in wet conditions.
THE GSI DIFFERENCE
Step 1
We assess the slab condition, underlying ground, and void extent. The assessment determines whether slab lifting is appropriate, what resin quantity and port pattern is required, and whether any underlying ground treatment is needed alongside the resin injection.
Step 2
12–16 mm ports are drilled through the slab in the designed pattern. Resin is injected in controlled increments, with the slab level monitored continuously. Injection stops precisely when the target elevation is reached at each port location.
Step 3
Resin achieves working strength within 15–30 minutes. Injection ports are patched to match the slab surface, and the area is returned to traffic or use on the same day. A completion record of port locations and resin volumes is provided.
CAPABILITY
Polyurethane grouting is suited to domestic driveways, warehouse floors, carparks, industrial slabs, and infrastructure pavements alike. The same process (12–16 mm ports, expanding resin, same-day return to service) scales from a settled residential driveway to a large industrial floor or road pavement void.
Cured polyurethane is chemically inert, water-resistant, and maintains its volume and strength over time; it does not shrink or dissolve. For below-ground structural waterproofing, resin injection seals cracks and joints without excavation, providing a durable barrier to water ingress. GSI NZ deploys polyurethane grouting as part of a broader specialist grouting capability that includes foamed concrete, DSM, IMS, and jet grouting, so the right method is applied to every project.
Specialist Grouting Overview →SPECIALIST GROUTING
Ground improvement and foundation works for major Christchurch aquatic facility.
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126 soil-cement columns to stabilise an active landslide mass, Central Hawke's Bay.
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Soft ground improvement beneath a wastewater treatment plant without excavation.
View Project →Get in Touch
Void filling, slab lifting, or pipe annulus grouting — our polyurethane grouting teams work with minimal disruption and deliver results you can see immediately.
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