Sealing Active Leaks in Commercial Concrete Structures
Polyurethane crack injection stops water leaking through cracks, joints and voids in concrete by injecting a liquid resin that reacts with moisture, expands and cures into a flexible, watertight seal inside the crack. Because the resin needs water to react and stays flexible once cured, it is the standard repair for actively leaking cracks in parking garages, foundation walls and elevator pits, including cracks that continue to move.
Nusite Group performs polyurethane injection on condominium, rental and office towers, and on commercial, institutional and industrial buildings across the GTA and Southern Ontario. The work is done from the interior side of the structure, so a leak can be sealed without excavation and without taking the space out of service for long.
Discuss Your Injection Waterproofing Project
A leaking crack in an existing parking garage, foundation wall or elevator pit can usually be sealed from inside the structure, without excavation or closing the space for long.
Nusite Group can review the leak, confirm whether polyurethane injection or another system suits the crack, and plan the work around the building’s operations.
When Polyurethane Injection Is the Right Repair
Polyurethane is the first choice where water is the problem and the crack is not structural. It suits:
- Cracks and joints that are actively leaking or wet
- Non-structural shrinkage, settlement and thermal cracks, from hairline width upward
- Cracks that open and close with temperature, traffic or seasonal movement
- Cold joints and construction joints in walls and slabs
- Voids and honeycombing around pipe and service penetrations
It is not the right repair for every crack. A structural crack in a load-bearing slab, wall or beam needs structural epoxy injection to restore strength. Water entering across a whole wall rather than at a defined crack calls for curtain grouting. A failed membrane beneath a deck or slab is better addressed with GTI-1000 no-excavation injection.
Hydrophilic and Hydrophobic Polyurethane
Polyurethane injection resins fall into two families, and the choice depends on how much water is present and how the crack behaves.
Hydrophilic Polyurethane
Hydrophilic resins absorb water as they react, forming a flexible foam or gel that bonds to damp concrete. They suit cracks that stay consistently wet, and their flexibility accommodates ongoing movement.
Hydrophobic Polyurethane
Hydrophobic resins repel water as they cure, forming a closed-cell foam with minimal shrinkage when the crack later dries out. They suit higher water flow and cracks that cycle between wet and dry, as many parking structure cracks do through the year.
In practice the resin, its reaction time and the port spacing are selected for each crack after the assessment, not standardized across a project.
High-Pressure Injection
Most polyurethane injection on commercial structures is carried out at high pressure. An injection pump drives the resin through mechanical packers set into drilled ports, forcing it to the full depth of the crack and into connected voids before it reacts.
High-pressure injection is used where:
- Walls and slabs are thick and the crack must be filled through its full depth
- Water is flowing and the resin has to displace it before setting
- Cracks are fine, and low-pressure or surface-applied methods will not penetrate
- Leaks track along joints and voids rather than a single visible crack
Pressure is controlled throughout. Too much pressure, too fast, can blow out the crack face or push resin away from the leak path, so injection progresses port by port while the operator watches for resin at the next port.
The Polyurethane Injection Process
- Assessment. We trace the leak, confirm the crack is non-structural, and select the resin and injection pressure.
- Port layout. Ports are drilled at an angle so they intersect the crack within the thickness of the concrete, alternating either side of it at set intervals.
- Flushing. Where needed, ports are flushed with water to clear debris and pre-wet the crack for the resin to react.
- Packers. Mechanical injection packers are set in each port.
- Injection. Resin is injected at controlled pressure, starting at the lowest port on vertical cracks and moving upward as resin appears at the next port.
- Finishing. Once the resin has cured, packers are removed and the ports are patched.
- Verification. The repair is checked for residual seepage, and any remaining wet spots are re-injected.
Where We Use Polyurethane Injection
- Underground parking garages beneath condominium, rental and office towers: leaking slab cracks, construction joints and column bases, sealed level by level so parking stays in service.
- Foundation walls and below-grade slabs: shrinkage and settlement cracks, cold joints and tie holes in occupied buildings, including walls with no exterior access.
- Elevator pits: active leaks at the wall-to-floor joint and through pit walls, scheduled with the building operator and the licensed elevator contractor.
- Pipe and service penetrations: voids around penetrations through below-grade walls where water concentrates.
- Mechanical, electrical and storage rooms below grade, where water reaching equipment becomes an operations problem as well as a building envelope one.
- Tunnels and service corridors: leaking cracks and construction joints in below-grade connections and infrastructure.
Polyurethane vs. Epoxy Crack Injection
The two materials solve different problems, and choosing the wrong one is a common reason injection repairs fail.
| Polyurethane | Epoxy | |
|---|---|---|
| Purpose | Stops water | Restores structural strength |
| Crack condition | Wet or actively leaking | Dry or nearly dry |
| Cured state | Flexible foam or gel | Rigid, high-strength bond |
| Movement | Accommodates ongoing movement | Does not; a moving crack can reopen beside the repair |
| Typical use | Shrinkage cracks, cold joints, penetrations | Structural cracks in slabs, walls and beams |
Some cracks need both: polyurethane to stop the water first, then epoxy to restore strength once the crack is dry. For a fuller comparison that includes polymer gel, see Injection Waterproofing Materials: Polymer Gel vs. Polyurethane vs. Epoxy.
Why Injection Repairs Fail, and How We Prevent It
Most failed crack injections trace back to execution or material choice rather than the resin itself.
- Ports that miss the crack. If drilled ports do not intersect the crack within the wall, resin seals the surface and water finds a way around it. We set port angle and spacing against the wall thickness.
- Wrong material. Epoxy in a wet, moving crack, or polyurethane in a structural crack, will not hold. Material is selected after the crack is assessed.
- Excess pressure or speed. Injecting too fast can blow out the crack face or leave voids. Pressure is controlled and injection progresses port by port.
- Untreated leak paths. Water often travels along joints and voids to the visible crack. Tracing the actual entry point is part of the assessment.
- No follow-up. Residual seepage is checked after cure and re-injected rather than left to grow.
Built for Southern Ontario Conditions
Road salt tracked into parking structures each winter, freeze-thaw cycling and thermal movement keep cracks in GTA structures opening and closing. A flexible polyurethane seal moves with them, which is why it is the default for leaking, non-structural cracks in parking garages and below-grade walls across the region.
Why Project Teams Choose Nusite Group
- Established in 1990, serving the GTA and Southern Ontario
- Fully bonded, licensed across Ontario, up to $10 million in liability coverage
- Injection scopes self-performed by Nusite crews, not brokered to a third party
- Material and labour warranties, with coverage varying by system and scope
- Experience coordinating with property managers, condominium boards, facility teams and general contractors
Polyurethane injection is one of four injection systems we install. See all methods on our Commercial Injection Waterproofing page.
FAQ
What is polyurethane injection waterproofing?
It is a crack repair method in which a liquid polyurethane resin is injected under pressure through ports drilled into a leaking crack or joint. The resin reacts with the water present, expands to fill the crack and cures into a flexible seal that stops the leak from inside the concrete.
Is polyurethane good for sealing concrete cracks?
For leaking, non-structural cracks, yes. It bonds to damp concrete, fills the crack through its depth and stays flexible, so it holds where cracks continue to move. It does not restore structural strength; structural cracks need epoxy.
How does polyurethane injection compare with epoxy injection?
Polyurethane stops water and stays flexible; epoxy restores strength and cures rigid. Polyurethane is used on wet or moving cracks, epoxy on dry structural cracks. Some cracks are treated with both.
Which concrete cracks are suitable for polyurethane injection?
Actively leaking or damp non-structural cracks, from hairline width upward, including shrinkage, settlement and thermal cracks, cold joints, tie holes and voids around penetrations.
Can polyurethane injection permanently stop water leaks?
A correctly selected and installed polyurethane injection is a long-term repair, because the seal sits inside the crack and moves with it. Its service life depends on the crack, the movement in the structure and the water pressure behind it. Our injection work carries material and labour warranties, with coverage varying by system and scope.
Can polyurethane be injected from inside the building?
Yes. Injection is carried out from the interior face of the wall or slab, with ports drilled to intersect the crack within the concrete. That is why it suits parking garages, elevator pits and foundation walls where the exterior cannot be reached.
What is the difference between hydrophilic and hydrophobic polyurethane?
Hydrophilic resin absorbs water as it reacts and suits cracks that stay consistently wet. Hydrophobic resin repels water as it cures, shrinks less when the crack dries out, and suits higher water flow and cracks that cycle between wet and dry.
What causes polyurethane crack injection to fail?
Usually execution: ports that do not intersect the crack, injecting too fast, using polyurethane on a structural crack, or treating the visible crack while water enters elsewhere. Careful layout, controlled pressure and tracing the actual leak path prevent most failures.
What areas do you serve?
We serve the Greater Toronto Area and Southern Ontario on commercial, institutional, industrial and multi-residential projects.
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