Injection grouting — questions answered

Injection grouting is a trenchless method for stopping active water infiltration in pipes, joints, cracks, and voids. A low-viscosity resin — typically polyurethane or acrylic — is injected under pressure through small drilled ports directly into the defect. When the resin contacts water, it expands and cures to form a flexible, watertight seal.

Because the work is done from the inside of the structure, injection grouting eliminates the need for excavation, road closures, or service interruptions in most cases. It is widely used by municipalities, strata corporations, and civil engineers as a faster, lower-cost alternative to dig-and-replace for sealing leaking sewers, foundations, manholes, and marine structures.

The choice of resin comes down to the defect type and flow conditions.

Polyurethane grout is hydrophobic — it repels water and expands aggressively on contact with moisture. This makes it ideal for active leaks under live flow, pipe joint infiltration, and discrete cracks where water is visibly entering. It cures quickly, handles structural movement well, and produces a durable flexible seal.

Acrylic grout (also called acrylate or acrylamide grout) is hydrophilic — it absorbs water and forms a softer gel-like seal. It has a very low viscosity, allowing it to penetrate fine cracks and permeable soil zones that polyurethane cannot reach. It is the preferred resin for curtain grouting, permeation grouting, and sealing diffuse seepage through fine cracks.

We specify the correct resin — or combination of resins — for each application based on defect type, substrate, and flow conditions after CCTV inspection.

Yes, when correctly specified and applied. Cured polyurethane resins are flexible, chemically resistant, and resistant to UV, biological growth, and the wet environments they are designed for. They accommodate minor structural movement without cracking. Repairs in municipal sewer mains and below-grade structures routinely last 20 or more years.

That said, grouting seals the defect as found — if the surrounding structure continues to deteriorate significantly (for example, severely corroded pipe wall, ongoing ground movement), additional work may eventually be needed. Our post-job CCTV verification confirms every seal is holding before we close out the job.

Injection grouting is effective across a wide range of below-grade and submerged structures: sanitary and storm sewer mains and laterals, manholes and access chambers, below-grade parking structures and parkade slabs, concrete foundation walls, elevator pits and sump pits, water reservoirs and chambers, seawalls and abutments, and submerged marine structures.

The common requirements are that the defect allows resin injection under pressure, and that the host structure is sound enough to accept a grouted repair. Our CCTV scoping process confirms suitability before we commit to a scope of work.

The right solution depends entirely on what CCTV inspection reveals about the condition of the pipe or structure.

Grouting is the correct choice when defects are localised — active joint infiltration, isolated cracks, or point defects — and the host pipe is otherwise structurally sound. It is the fastest and lowest-cost solution for infiltration problems.

Pipe lining (CIPP or slip lining) is better suited when a pipe has widespread deterioration across its length but still has sufficient structural integrity to act as a host for a liner.

Full replacement is warranted when the pipe has collapsed sections, major root intrusion throughout, or is beyond structural rehabilitation.

We will give you an honest assessment of which approach fits your situation after reviewing the CCTV footage. Grouting is not always the right answer, and we will tell you that clearly if it is not.

Inflow is stormwater entering the sanitary sewer system through direct connections — open or damaged manhole lids, illegal roof drain tie-ins, or surface openings. Infiltration is groundwater entering through cracks, defective joints, or deteriorated pipe walls, particularly during wet weather when the water table is elevated.

Both overload treatment capacity and can trigger combined sewer overflows (CSOs) and bypasses, with associated regulatory and environmental consequences. Injection grouting directly addresses infiltration by sealing the specific joints and cracks through which groundwater enters. A CCTV-guided grouting programme can dramatically reduce wet-weather peak flows and I&I volumes — without the cost and disruption of excavation or full pipe replacement.

Curtain grouting (also called perimeter or blanket grouting) creates a continuous waterproof barrier in the soil surrounding a structure, rather than sealing a single discrete crack or joint. Resin is injected at multiple closely-spaced points to form an overlapping curtain that intercepts groundwater before it reaches the structure.

It is used when water is migrating through permeable soil or through many fine cracks that cannot be individually targeted — for example, to waterproof an entire below-grade wall face, to seal around a pipe penetration through a wall, or to stop diffuse seepage across a large area. Acrylic (acrylate) resins are commonly used for curtain grouting because of their very low viscosity and good soil penetration.

Yes — and this is one of its primary advantages for building owners and strata corporations. Excavating externally to waterproof a foundation is extremely disruptive and expensive, requiring removal of landscaping, hardscaping, and often closing adjacent spaces for weeks.

Injection grouting through the interior face eliminates that disruption. We drill through the concrete wall at an angle to reach the crack plane or the exterior face, inject resin that travels outward and cures against the water pressure, and the resulting seal holds from the outside in. This approach is widely used in parkades, below-grade mechanical rooms, elevator pits, and residential foundations throughout the Lower Mainland.