This article is for informational purposes only and does not constitute professional engineering or construction advice. Foundation work that may affect structural integrity requires assessment by a licensed professional engineer.
Foundation cracks in Canadian residential buildings range from cosmetic shrinkage lines to indicators of ongoing structural movement. The appropriate repair approach depends on crack type, cause, and whether the crack is active (still widening) or dormant (stable). Applying a repair to an active crack without addressing the underlying cause typically results in recurrence.
Crack Classification
Before selecting a repair method, cracks are typically assessed across three dimensions: orientation, width, and activity.
Orientation
- Vertical cracks: Most common in poured concrete walls. Usually result from concrete shrinkage as it cures. Shrinkage cracks typically appear within the first few years and stabilize. They allow water ingress but are not structurally significant in isolation.
- Horizontal cracks: Located mid-wall height in poured concrete, or at mortar joints in block walls. Indicate lateral pressure — soil load, frost, or surcharge loads. More structurally significant than vertical cracks. Horizontal cracks that are measurably widening require professional assessment.
- Diagonal cracks: Often appear at corners or where concentrated loads bear on the foundation. May indicate differential settlement. Stair-step cracking in concrete block walls is a diagnostic pattern for settlement-related movement.
Width
Width classification is a rough guide, not a definitive threshold:
- Under 0.3 mm: Within normal tolerance for concrete; typically addressed with waterproofing rather than structural repair
- 0.3–0.6 mm: Warrants documentation and monitoring; repair depends on location and activity
- Over 0.6 mm: Generally treated as requiring repair; wider cracks are more likely to allow water infiltration and are more likely to be associated with movement
Activity
A dormant crack can be treated definitively. An active crack requires the cause of movement to be identified and addressed — or the repair material must be capable of accommodating further movement (flexible sealants or polyurethane foam rather than rigid epoxy).
Simple activity monitoring: mark the crack ends with pencil and date, or apply a crack monitor (tell-tale). Reassess after one full seasonal cycle before committing to a permanent repair method.
Epoxy Injection
Epoxy injection is used on dormant cracks where the goal is structural restoration — bonding the two crack faces to restore tensile continuity across the section. Cured epoxy is typically stronger than the surrounding concrete in compression, and achieves bond strength comparable to the parent material in tension.
Process
Injection ports are inserted at intervals along the crack — spacing depends on crack depth and width, but 200–300 mm centres are common. The crack face is cleaned and the surface sealed with epoxy paste, leaving the ports open. Low-pressure injection is applied at the lowest port until epoxy appears at the next port, which is then capped, and injection continues upward. The cure period before loading is typically 24–72 hours depending on temperature and product specification.
Limitations
Epoxy injection is not appropriate for active cracks, wet or damp cracks (epoxy does not bond well to wet concrete surfaces), or cracks associated with ongoing structural movement. It does not address the cause of cracking — a wall that is moving due to soil pressure will re-crack adjacent to or through an epoxy repair.
Polyurethane Foam Injection
Polyurethane foam injection is the standard approach for sealing leaking cracks where the primary goal is waterproofing rather than structural restoration. The foam expands on contact with moisture — which is present in most actively-leaking cracks — and cures to a flexible, compressible plug that accommodates minor crack movement.
Process
The procedure is similar to epoxy injection in terms of port placement and sequential filling. The reacting foam fills the crack volume and any connected voids within the wall section. Because the cured foam is flexible, it is preferred for cracks in walls subject to seasonal movement — the foam compresses and expands slightly as the crack width changes with temperature and soil moisture cycles.
Hydrophilic vs. Hydrophobic Formulations
Polyurethane foams used in crack injection come in two formulations. Hydrophilic foams require moisture to cure and expand — they are suited for wet conditions but may shrink back slightly if the crack dries completely after repair. Hydrophobic foams cure regardless of moisture presence and maintain their volume in dry conditions. Product selection depends on the anticipated long-term moisture environment at the crack.
Wall Anchors and Carbon Fibre Straps
Where a wall shows signs of inward bowing from soil pressure — particularly in block walls with horizontal cracks — injection methods alone are insufficient. Lateral reinforcement is required.
Carbon Fibre Straps
Carbon fibre reinforcing straps are bonded vertically to the interior wall face using epoxy. The straps resist further inward movement by transferring lateral load to the floor slab above and below. They do not reverse existing deflection — they arrest progression. This approach is appropriate for walls with deflection up to roughly 50 mm from plumb; beyond that threshold, more invasive intervention may be needed.
Wall Anchors
Steel wall anchors consist of an interior plate connected by a rod to an exterior buried plate in the undisturbed soil beyond the active failure zone. Anchors can be incrementally tightened over time to gradually reduce wall deflection — a slow process that must be managed carefully to avoid introducing new cracks. Installation requires drilling through the wall and excavating anchor holes beyond the failure zone, which may not always be accessible.
Underpinning
Underpinning involves extending the foundation to greater depth to bear on competent soil, arrest settlement, and in some cases lower the basement floor. It is among the more involved foundation repair procedures and is typically undertaken when conventional crack repair cannot address the root cause — inadequate bearing depth or severely deteriorated original footings.
Mass Concrete Underpinning
The original and most common method: the soil beneath existing footings is excavated in alternating sections (pins), concrete is poured in each section, allowed to cure, and the load is progressively transferred to the new concrete. The alternating sequence maintains support under the wall at all times during the process.
Helical Piers
Helical steel piers are screwed into the ground through the footing to bearing depth using hydraulic equipment. They transfer building load directly to competent soil or bedrock, bypassing the poor-bearing soil that caused settlement. Pier installation is less disruptive than mass concrete underpinning and is increasingly common in residential applications across Canada where access permits.
Micro-piles
Small-diameter drilled piles (typically 150–250 mm) grouted into the ground. Used where load transfer requirements exceed what helical piers provide, or in restricted access conditions.
Permits and Engineering
In most Canadian municipalities, foundation repair that affects structural elements — including underpinning, wall anchor installation, and any work on load-bearing components — requires a building permit and may require drawings prepared by a licensed professional engineer. Injection sealing of non-structural cracks for waterproofing purposes may fall below the permit threshold in some jurisdictions, but confirming with the local building department before work begins is the appropriate step.
The NBC 2020 and provincial codes establish the minimum standards; local amendments can affect what requires approval.
When to Involve a Structural Engineer
Certain crack patterns indicate structural conditions that require professional assessment before any repair is attempted:
- Any horizontal crack in a basement wall, particularly if widening
- Cracks accompanied by visible wall deflection (out-of-plumb walls)
- Stair-step cracking in block or brick foundations with evidence of movement
- Cracks above or below openings (windows, doors) that are widening
- Settlement cracks in the superstructure — floors sloping, door frames racking, diagonal cracks at window corners