A New Waterproof Barrier Behind the Wall, Without Excavation
Curtain grouting stops water coming through a below-grade wall or slab by drilling through the structure and injecting grout into the soil on the other side. The grout fills the voids in the soil and gels or cures into a continuous barrier, a “curtain”, against the outside face of the wall. It replaces a waterproofing layer that has failed or never existed, from inside the building, without excavating.
Nusite Group installs curtain grouting on condominium, rental and office towers, and on commercial, institutional and industrial buildings across the GTA and Southern Ontario. It is sometimes called curtain wall grouting or curtain injection; it is unrelated to glazed curtain wall facades.
Discuss Your Injection Waterproofing Project
Seepage through a below-grade wall can usually be stopped from inside the building, without excavating or disturbing what sits outside the wall.
Nusite Group can review the seepage, confirm whether curtain grouting or another injection system suits the wall, and plan the work around the building’s operations.
When Curtain Grouting Is the Right Repair
Curtain grouting treats an area rather than a single crack. It suits:
- Widespread seepage through a wall, rather than water at one defined crack
- Concrete block, masonry or honeycombed concrete walls where water passes through the wall itself
- Leaks at the wall-to-floor joint and along the base of foundation walls
- Walls where the exterior waterproofing has failed or was never installed
- Walls with no exterior access: zero lot line walls, walls against an adjacent building, or walls beneath hardscape
Where water enters at a defined crack, polyurethane crack injection is usually faster. Where an existing membrane has failed beneath a deck or slab, GTI-1000 no-excavation injection restores the membrane plane itself.
How a Grout Curtain Works
Holes are drilled through the wall in a grid, all the way to the soil behind it. Grout is pumped through each hole and spreads into the soil, filling the voids between soil particles. As injection moves from hole to hole, the grout from each one meets the next and forms a continuous layer against the positive side of the wall.
Because the barrier sits on the water side of the structure, water is stopped before it reaches the concrete. That differs from interior coatings, which hold water inside the wall and can leave the concrete saturated.
Curtain Grout Materials
The grout is selected for the soil, the volume of water and the structure.
Acrylic Gel
Very low-viscosity grouts that penetrate fine soils and fine cracks, then set into a flexible gel. They are a common choice for curtain grouting because they spread readily through the soil behind a wall.
Polyurethane
Hydrophilic polyurethane expands in contact with water to form a flexible seal. Hydrophobic polyurethane forms a foam that holds up in higher water flow. Polyurethane is often used to cut off active flow before or alongside the curtain.
Silicate
Silicate grouts react to form a gel and are used for damp-proofing and stabilizing loose soils, rather than stopping active leaks.
Cementitious Grout
Cement-based grouts fill large voids and stabilize soil behind the wall. They are less flexible, so they are used where movement is limited, often together with a chemical grout.
The Curtain Grouting Process
- Assessment. We map the seepage, review the wall construction and what is behind it, and select the grout.
- Layout. Injection holes are laid out in a grid across the affected area, with spacing set for the soil and grout.
- Drilling. Holes are drilled through the wall to the soil behind it, with care taken around utilities and adjacent structures.
- Packers. Injection packers are set in each hole.
- Injection. Grout is pumped under controlled pressure, typically starting at the bottom row and working upward, until it spreads to the neighbouring holes.
- Cure. The grout gels or cures in the soil to form the barrier.
- Finishing and inspection. Packers are removed, holes are patched, and the wall is checked for remaining seepage.
Where We Use Curtain Grouting
- Elevator pits and sumps in condominium, rental and office towers, where groundwater collects at the lowest point of the building.
- Below-grade walls in parking garages and storage levels, including block and masonry walls in older buildings.
- Zero lot line and party walls built against an adjacent building or shoring, with no exterior access.
- Mechanical, electrical and utility rooms below grade, where water reaching equipment affects operations.
- Vaults, tunnels and service corridors connecting below-grade structures.
Curtain Grouting vs. Other Injection Methods
| Curtain grouting | Polyurethane crack injection | GTI-1000 injection | |
|---|---|---|---|
| Where the material goes | Into the soil behind the wall | Into the crack | To the existing membrane plane |
| What it treats | Area-wide seepage | A defined crack or joint | A failed membrane under a deck, slab or wall |
| Best for | Porous, block or unprotected walls | Leaking shrinkage cracks and cold joints | Podiums, plaza decks, parking slabs |
| Excavation | None | None | None |
See all four methods on our Commercial Injection Waterproofing page.
What We Check Before Curtain Grouting
Curtain grouting works with the soil behind the wall, so the conditions there are checked before work starts:
- Soil type. Fine soils need lower-viscosity grouts; open, gravelly fill may need a cementitious grout first.
- What is behind the wall. Utilities, foundation drains and adjacent structures are located so drilling and grout do not affect them.
- Water volume. High flows are cut off first so grout is not washed away before it sets.
- Structural condition. Deteriorated walls may need repair alongside the grouting.
Southern Ontario Conditions
Soil and fill conditions behind foundation walls vary widely across the GTA, from clays to granular backfill, and many older buildings have block or masonry foundations with no exterior membrane at all. Matching the grout to the soil, rather than using one material everywhere, is what makes the curtain continuous.
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 of 5 to 15 years on curtain grouting, depending on the materials used and the scope
- Experience coordinating with property managers, condominium boards, facility teams and general contractors
FAQ
What is curtain grouting?
Curtain grouting is a waterproofing repair in which holes are drilled through a below-grade wall or slab and grout is injected into the soil behind it. The grout spreads through the soil and sets into a continuous barrier against the outside face of the structure, stopping water before it reaches the wall.
How does curtain grouting work?
Grout is pumped through a grid of holes drilled through the wall. Each injection spreads into the soil until it meets the grout from the neighbouring holes, building a continuous curtain on the water side of the wall.
What materials are used for curtain grouting?
Acrylic gels, hydrophilic and hydrophobic polyurethanes, silicate grouts and cementitious grouts. The choice depends on the soil, the water volume and the structure; projects often combine two.
Does curtain grouting work?
Yes, when the grout is matched to the soil and the injection grid is close enough for the grout from each hole to meet the next. It is a proven method for stopping groundwater seepage through below-grade walls without excavation.
When is curtain grouting used instead of crack injection?
When water is coming through a whole area of wall rather than one crack: porous or block walls, walls with no exterior waterproofing, and seepage along the base of a wall. Defined cracks are usually sealed faster with polyurethane crack injection.
Is curtain grouting the same as curtain wall injection?
The terms are used interchangeably for grouting behind below-grade walls. It has nothing to do with glazed curtain wall facades.
Does curtain grouting require excavation?
No. All drilling and injection is done from inside the building, which is why it is used on zero lot line walls, walls beneath hardscape and walls against adjacent buildings.
What warranty comes with curtain grouting?
Our curtain grouting is backed by material and labour warranties, typically 5 to 15 years depending on the materials used and the scope of the project.
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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