Foundation cracks are the single most common entry point for water in Ontario homes. Every crack is a direct path from saturated soil to your basement interior — and every season it stays open, it gets wider. We identify the type, find the cause, and seal it permanently.
Concrete naturally cracks. As it cures, it shrinks. As the foundation settles over decades, it moves. As Ontario winters push frost deep into the soil, it heaves. As spring snowmelt saturates the ground, hydrostatic pressure builds against the wall. Every one of these forces can produce a crack — and every crack is a potential water entry point that may require basement waterproofing intervention.
The key to effective foundation crack repair is diagnosis before repair. A hairline shrinkage crack in poured concrete — the thin vertical line you might find in a new foundation — is fundamentally different from a horizontal crack caused by lateral soil pressure pushing against a block wall. The right repair method depends entirely on understanding what type of crack you're dealing with and why it formed.
Polyurethane injection seals an actively leaking vertical crack in poured concrete. Epoxy injection restores structural integrity to a dry, stable crack. Carbon fibre strapping stabilizes a bowing wall before any crack repair makes sense. Exterior waterproofing excavation addresses cracks that have damaged the waterproof membrane on the exterior face. Each situation calls for a specific method — and applying the wrong one means the repair fails, often quickly.
At AW Waterproofing Solutions, we assess every crack before we recommend a repair. We look at the crack type, orientation, width, depth, whether it's active or dormant, and what the surrounding drainage and soil conditions look like. That assessment is what separates a repair that lasts from one that needs to be redone. We serve Napanee, Belleville, Kingston, Deseronto, Bath, and surrounding communities throughout Lennox and Addington County and the Bay of Quinte region.
Some foundation cracks are immediately obvious. Others hide behind drywall, beneath paint, or reveal themselves only through secondary symptoms — moisture, odour, or mineral deposits. These are the signs we look for and what each one tells us about what's happening inside the foundation.
Thin vertical lines in poured concrete, often the result of initial curing shrinkage. They look harmless — and structurally, they often are — but water under hydrostatic pressure finds them immediately. Small now, but they widen with every freeze-thaw cycle.
Water visibly entering through a crack during or after rain or snowmelt is the clearest signal that immediate repair is needed. Active seeping cracks mean hydrostatic pressure outside the wall exceeds the crack's resistance — and the flow will increase as the crack widens.
The most serious crack type. Horizontal cracks are caused by lateral soil pressure against the wall — the same pressure that drives water in. They can indicate structural risk and require immediate professional assessment. Never treat a horizontal crack as a cosmetic issue.
Diagonal cracks, particularly those radiating from corners of windows or doors, often indicate differential settlement of the foundation footing — where one section of the foundation has moved more than another. Common at building corners and at transitions between foundation sections.
In block or brick foundations, cracks that follow the mortar joints in a staircase pattern signal settling or shifting. Step cracks allow water to travel along multiple mortar joints simultaneously and can indicate ongoing movement that needs to be arrested before crack sealing is effective.
White mineral deposits at crack edges are the mineral residue left behind as water moves through the concrete and evaporates at the surface. Efflorescence at a crack is confirmation that water has been regularly moving through it — whether the crack appears wet right now or not.
Mould growing inside a cracked wall or in the cavity behind a finished wall creates a distinctive musty odour before any visible signs appear. A persistent smell near a specific wall section is often the first indication of a crack hidden behind finishes — and of sustained moisture behind it.
Concrete chipping, flaking, or crumbling at the edges of a crack means freeze-thaw cycling is actively enlarging the crack. Water enters the crack, freezes, expands by roughly 9% in volume, and physically breaks the concrete at the crack face. Each winter, it gets worse.
Understanding the cause of a crack is as important as choosing the repair method. A crack repaired without addressing its underlying cause is likely to recur — at the same location or nearby. These are the most common causes we identify during foundation crack assessments in this region.
Concrete naturally shrinks as it cures and loses moisture. This shrinkage is the most common cause of vertical cracks in new poured concrete foundations. While typically non-structural, these cracks create direct paths for water under hydrostatic pressure and should be sealed before they widen through freeze-thaw cycling.
Water-saturated soil exerts enormous lateral and downward pressure against foundation walls. This hydrostatic pressure forces water through existing cracks and can create new ones in walls that were previously intact. It is the primary driver of active crack leaks after rain and snowmelt events in Ontario.
Ontario winters cause soil moisture to freeze and expand, pushing against foundations with considerable force. This pressure widens existing cracks and can create new ones, particularly at corners and wall-footing connections. Each freeze-thaw cycle compounds the damage from previous winters.
If one section of the foundation settles more than another — due to soil variation, compaction differences, or moisture changes beneath the footing — diagonal cracks appear at stress concentration points. These cracks often follow windows, doors, and corners where the wall geometry changes.
Roots from nearby trees actively seek moisture and can grow toward and against foundation walls, exerting sustained pressure that widens existing cracks and can damage drainage tile. Roots can also infiltrate weeping tile systems, blocking drainage and keeping soil consistently saturated around the foundation.
Soil that doesn't drain away from the foundation keeps the wall under constant hydrostatic pressure. Poor grading, blocked or failed weeping tile, absent or damaged drainage board, and downspouts discharging against the foundation all contribute to chronic soil saturation that drives crack formation and water intrusion.
Older poured concrete and concrete block foundations become more porous and more susceptible to cracking over decades of weather exposure, freeze-thaw cycling, and carbonation. Block foundations in particular allow water to migrate through hollow cores and mortar joints even without obvious discrete cracks.
Excessive weight above the foundation — heavy additions, large machinery, or changes to the home's structural load paths — can create stress cracks where the load concentrates. These cracks are typically vertical to diagonal and appear at points where load transfer is concentrated, such as under beams or posts.
The right repair depends on the crack type, its cause, whether it is active or dormant, and the foundation material. We match the method to the situation — not the other way around. Here is what each approach involves and when we recommend it.
The gold standard for actively leaking cracks in poured concrete foundations. Injection ports are installed along the crack face at regular intervals and sealed with surface paste. A two-part polyurethane resin is then injected under controlled pressure, travelling through the crack from face to exterior.
As the resin contacts moisture inside the crack, it expands — filling irregular voids, bonding to the wet concrete surfaces, and curing into a flexible, waterproof seal. The flexibility is the critical differentiator: it allows the sealed crack to accommodate minor foundation movement without re-cracking, which is why polyurethane injection outlasts rigid surface repairs in the vast majority of cases.
Polyurethane injection can be performed while the crack is wet or actively leaking. It requires no excavation and is typically completed in a single visit. It is the most widely applicable crack repair method for poured concrete foundations.
Actively Leaking Cracks Poured Concrete Flexible Seal No Excavation RequiredUsed for structural crack repair where rigidity is the priority rather than flexibility. Epoxy injection bonds the two sides of a crack together with a material that — when fully cured — exceeds the tensile strength of the surrounding concrete. The crack is effectively welded shut.
Epoxy injection is the right choice for dry, dormant cracks where the goal is to restore the structural integrity of the wall across the crack face — not just to seal it against water. It is not appropriate for active or moving cracks: a rigid epoxy repair in a crack that is still experiencing movement will re-crack alongside the injection rather than holding.
We select epoxy injection for specific situations — particularly after carbon fibre strapping has stabilized a moving wall, or for settlement cracks that have been monitored and confirmed dormant. The method requires the crack to be dry before injection begins.
Structural Cracks Dry Cracks Only Restores Tensile Strength Rigid BondWhen a crack extends through the full depth of the wall and has compromised the exterior waterproof membrane — or when the crack is wider at the exterior face than the interior — addressing it from the outside is the most thorough approach. We excavate to expose the exterior wall face at the crack location, clean and prepare the surface, and apply a Duraflex rubberized membrane patch over the crack and surrounding area.
Over the membrane patch, we install drainage board to protect the membrane and restore the drainage plane. This ensures water is directed downward to the weeping tile rather than building pressure against the repaired section. The crack may also be injected from the interior simultaneously for a complete two-sided repair.
Exterior crack repair requires more disruption than interior injection but addresses the problem at its source — the exterior face where water contacts the wall first. For cracks in situations where the membrane has clearly failed, it is the most durable long-term solution.
Duraflex Membrane Patch Drainage Board Full-Depth Cracks Exterior AccessFor horizontal cracks or walls showing signs of bowing or inward movement, structural stabilization must come before crack sealing. Carbon fibre straps are bonded to the interior wall face using high-strength epoxy, anchoring at the floor and the rim joist above to prevent any further inward movement of the wall.
Carbon fibre strapping does not reverse existing movement — it stops further movement from occurring. Once the wall is stabilized, the crack can be sealed effectively because the movement that was causing or worsening the crack has been arrested. Attempting to seal a moving crack without stabilizing the wall first produces a repair that re-opens.
We recommend professional structural assessment alongside carbon fibre strapping for any horizontal crack. The degree of wall movement, the condition of the footing, and the drainage conditions all factor into whether strapping alone is sufficient or whether additional remediation is warranted.
Horizontal Cracks Bowing Walls Structural Stabilization High-Strength Epoxy BondIn situations where crack repair alone is not sufficient — multiple cracks across a block wall, a porous foundation that allows water to migrate through the wall material even without discrete cracks, or where additional insurance against future cracking is desired — an interior drainage system provides a permanent secondary layer of protection.
A perimeter drainage channel at the base of the foundation walls intercepts any water that enters through cracks or through the wall face and directs it to a sump pump before it can damage flooring or contents. The basement remains dry even if minor seepage occurs through the wall.
Interior drainage is particularly effective in older block foundations where the number and character of potential water entry points makes sealing every joint impractical. We often recommend it in combination with crack repair in these situations rather than as a standalone alternative to addressing the cracks directly.
Multiple Cracks Block Foundations Permanent System Sump Pump IntegrationFoundation crack repair sounds straightforward — inject the crack, done. The reality is that the correct diagnosis, the right material selection, and the quality of the injection technique determine whether a repair lasts five months or five decades. A wet basement may require crack injection alongside a drainage system for complete protection. Here is what we bring to every crack repair job.
We identify the crack type and underlying cause before recommending a repair method. The right fix depends on understanding why it cracked, whether it is active or dormant, and what the drainage conditions look like. We don't inject first and ask questions later.
For crack repairs requiring exterior membrane work, we use Duraflex rubberized systems — the same materials that protect full foundation excavations. Certified application means the membrane performs as designed, not as roughly approximated.
We don't fill cracks from the surface. Pressure injection forces repair material through the full depth of the crack from face to exterior, filling voids and bonding to the concrete throughout. Surface patching fails. Pressure injection holds.
Every crack repair comes with a written workmanship guarantee. If the repaired crack leaks again due to our work, we return and address it at no cost. The warranty is in writing before work begins — not a verbal assurance after the fact.
We know the soil conditions, frost depths, and water table behaviour in Napanee, Kingston, and Belleville. Our diagnosis is informed by years of working in these specific conditions — not generic assumptions that may or may not apply to Eastern Ontario.
Water entering your foundation through a crack shouldn't wait weeks for attention. We prioritize active leak repairs and provide clear timelines from first call to completion. When water is actively entering a home, we treat it with the urgency it deserves.
When a foundation crack requires exterior attention — because it has compromised the waterproof membrane at the exterior wall face, or because the crack is wider on the outside than the inside — the membrane patch material matters as much as the technique.
We use Duraflex rubberized membrane for all exterior crack patch work. Unlike rigid coatings or tar-based compounds, Duraflex bonds directly to concrete — including wet or damp concrete surfaces — and cures into a permanently flexible waterproof layer. That flexibility is critical for crack repair: a rigid patch over a crack that experiences any future thermal or settlement movement will fail at the edge of the patch. A Duraflex patch moves with the concrete.
Through Ontario's freeze-thaw cycles — where temperatures may cross the 0°C threshold repeatedly through a single winter — a flexible membrane holds while a rigid one cracks. After twenty winters, a correctly applied Duraflex patch is still performing. Tar compounds and rigid coatings applied by other contractors are typically brittle and delaminating long before that.
Professional-grade rubberized waterproofing membrane. The standard for certified foundation waterproofing and crack repair across Canada.
AW Waterproofing Solutions holds Duraflex installer certification. When we perform exterior crack repair, you're getting trained applicators who understand surface preparation, penetration detailing, and the application standards that determine whether a membrane patch performs over decades — not just until the next heavy rain.
After repairing hundreds of foundation cracks across Napanee, Kingston, and Belleville, certain patterns repeat. These are the real-world observations that don't come from manufacturer literature — the things you only learn by actually opening foundations and diagnosing what's happening inside them.
The crack looked hairline from the interior — barely 1mm wide at the wall face. When we excavated the exterior, it was 6mm wide and had clearly been channelling water for years. The exterior face of a crack is almost always wider than the interior face because hydrostatic pressure erodes the concrete outward. Surface patching from the inside would have failed within one season. Full-depth injection and an exterior membrane patch was the right answer.
A homeowner had the same crack injected three times by three different contractors over ten years. Each repair held briefly and then re-opened. When we assessed it, we found the root cause: blocked weeping tile keeping the surrounding soil permanently saturated and under maximum hydrostatic pressure. The crack injection was fine — but injecting into a wall under constant, unrelieved water pressure is fighting a losing battle. We replaced the weeping tile section and then repaired the crack. It hasn't re-opened.
A step crack in a block foundation at the back corner of the house that had been written off as cosmetic by two previous contractors. When we traced the drainage, we found a downspout discharging directly against that corner — concentrating every rainfall onto that one spot. The sustained saturation was causing differential settlement at the corner footing. Redirecting the downspout and extending it away from the foundation stopped the settlement. The crack was then sealed. A cosmetic fix without addressing the downspout would have failed within a season.
A horizontal crack in a 1960s block foundation wall that looked like it only needed sealing. The wall had a visible inward bow that the homeowner had assumed was "always like that." Installing carbon fibre strapping to stabilize the wall came first — trying to waterproof a wall that is still moving is futile. After strapping and sealing, the homeowner commented that the wall had actually been moving for years and had been written off as structural when it was a preventable, repairable condition. Earlier intervention would have been far less expensive.
The musty smell in the finished basement had been present for two years. The homeowner had it painted, treated for mould twice, and had the HVAC inspected. No one had removed the drywall section. When we did, we found a 2mm crack behind the vapour barrier — barely visible, not actively dripping, but consistently damp enough to sustain mould growth. Two millimetres is enough. Moisture finds any opening in a wall under hydrostatic pressure and exploits it relentlessly.
One properly repaired active crack changed a homeowner's sump pump cycle from running every hour during rain events to running twice a week. That single crack was responsible for the majority of the water load the pump was managing. The pump was not undersized — it was compensating for one leak. Fixing the source reduced the strain on the pump significantly and extended its service life. Not every sump pump that runs constantly needs to be replaced.
Tree roots had grown into the weeping tile over a 25-year period and were wicking moisture directly to a crack in the wall face. The crack was on the same side of the foundation as a large silver maple roughly four metres away. We replaced the blocked weeping tile section at the same time as repairing the crack — addressing both the drainage failure and the crack in one project. The crack repair alone, without the drainage work, would have been fighting the same conditions that caused the crack in the first place.
A diagonal settlement crack at the garage-to-house connection point — a classic location for differential movement, where two different foundation sections with potentially different footing depths meet. We injected with epoxy after monitoring confirmed the crack had been dormant for at least two seasons. We recommended annual monitoring for 12 months after repair to confirm the settlement had fully stabilized. Settlement cracks require patience in the diagnosis phase before the repair phase.
Many homeowners patch cracks with hydraulic cement or caulk from a hardware store. It stops visible water temporarily — sometimes for a season or two — and creates the impression the problem is solved. But hydraulic cement is rigid and doesn't bond well to concrete under hydrostatic pressure. It pops out. The caulk lifts. And the homeowner has lost another year while the crack widened slightly with each freeze-thaw cycle. The original crack repair would have been faster and cheaper than the repeated cycle of temporary fixes.
We repaired a crack that had been "fixed" three times by previous contractors. Each time it re-opened at the injection line within one to two years. The pattern was clear: all three previous repairs had used epoxy injection on a crack that was still moving seasonally with the foundation. Epoxy is rigid — it re-cracks when the foundation moves. The right material was flexible polyurethane. One injection with the correct material, and the repair has held. Material selection is as important as technique.
No single method suits every crack. The right choice depends on the crack type, whether it is active or dormant, the foundation material, and whether structural stabilization is needed before sealing. This comparison covers the primary methods we use and the situations each one best addresses.
| Method | Best For | Flexibility | Structural Benefit | Typical Use Case |
|---|---|---|---|---|
| Polyurethane Injection | Actively leaking or dormant vertical cracks in poured concrete | High — flexible cure, moves with foundation | Seals only — does not restore tensile strength | Active crack seeping during rain; most common crack repair scenario |
| Epoxy Injection | Dry, dormant cracks where structural integrity is the goal | None — rigid cure, cannot accommodate movement | High — exceeds surrounding concrete strength when cured | Confirmed dormant settlement cracks; post-stabilization structural repair |
| Exterior Membrane Patch | Full-depth cracks with exterior membrane damage | High — Duraflex stays flexible through freeze-thaw | Moderate — seals crack face and restores exterior barrier | Cracks wider at exterior than interior; failed exterior membrane at crack location |
| Carbon Fibre Strapping | Horizontal or bowing walls with active lateral movement | N/A — rigid stabilization system | High — prevents further inward wall movement permanently | Horizontal crack with bowing; prerequisite before crack sealing on moving walls |
| Interior Drainage System | Multiple cracks, block foundations, or where full sealing is impractical | N/A — manages water rather than sealing cracks | None — does not address the cracks themselves | Porous block walls; multiple entry points; backup layer alongside crack repair |
Homeowners ask these questions constantly when they call about a foundation crack. We give direct answers — no vague reassurances, no upselling language. If your question isn't here, call us.
Horizontal cracks are the most serious type. They indicate lateral soil pressure against the wall has exceeded the structural capacity of the wall itself — not just a water issue, but a structural risk. Diagonal cracks are the next most concerning, as they often indicate differential foundation settlement. Vertical cracks are typically the least structurally significant, though they are still water entry points and should be repaired. Any crack that is widening, offset (the two sides are at different levels), or associated with wall bowing requires immediate professional assessment.
Hardware store hydraulic cement and crack caulk can stop visible water temporarily — sometimes for a season or two. But surface patching doesn't address the hydrostatic pressure driving water through the crack, and it doesn't penetrate the full depth of the crack. It typically fails within one to two winters as the concrete moves and the patch lifts or cracks. Effective permanent crack repair requires pressure injection, which pushes repair material through the full depth of the crack under controlled pressure. This requires professional equipment and trained technique. DIY repairs delay the real repair while often making the crack harder to assess accurately.
We drill injection port holes along the crack face at intervals sized to the crack depth, install port fittings, and seal the crack surface between ports with a surface paste. A two-part polyurethane resin is then injected under controlled pressure through each port in sequence, starting at the lowest point. The resin travels through the crack — filling it from face to exterior — and reacts with moisture inside the crack, expanding to fill irregular voids. It cures into a flexible, permanently waterproof seal that is bonded to the concrete on both sides of the crack. The flexibility allows minor foundation movement to occur without re-opening the repair, which is why it outperforms rigid alternatives in most crack repair scenarios.
A correctly injected crack — filled to full depth with flexible polyurethane — will not re-open at the same location in the vast majority of cases. The repair is stronger than the original crack. However, if the underlying conditions that caused the crack are not addressed — high hydrostatic pressure from failed drainage, active settlement, blocked weeping tile — new cracks may form nearby even if the repaired crack holds. Our assessment identifies root causes so we can tell you whether crack repair alone is sufficient or whether drainage improvements should accompany the repair.
Polyurethane injection produces a flexible, expanding waterproof seal that bonds to wet or dry concrete and can accommodate minor foundation movement without re-cracking. It is the right choice for most actively leaking cracks and any crack in a foundation that experiences seasonal movement. Epoxy injection produces a rigid bond that can restore the tensile strength of concrete across the crack — making it stronger than the surrounding wall material. It is the right choice for dry, confirmed-dormant cracks where structural integrity is the repair priority. Using rigid epoxy in a crack that is still moving will result in the repair re-cracking alongside the injection line as the foundation moves.
Key indicators of a structural concern include: horizontal orientation, visible offset between the two sides of the crack (one side higher than the other), cracks wider than 6mm, cracks that are actively widening over time, and cracks associated with bowing or bulging of the wall. A hairline vertical crack in poured concrete that shows no movement, no offset, and no water entry is typically a cosmetic shrinkage crack. When you're uncertain, a professional assessment is the right call. The difference in consequences between a cosmetic crack and a structural one is too significant to guess at.
Most interior crack injection repairs are completed in a single visit of two to four hours, depending on the crack length and the number of ports required. Drilling, port installation, surface paste application, injection, and port capping are all done in one session. The injected polyurethane or epoxy cures within 24 to 48 hours, after which the repair is fully active. Exterior crack repairs requiring excavation take longer — typically one to two days depending on crack depth, wall height, and site access conditions.
Most crack repairs are performed from the interior using pressure injection, which is highly effective and requires no excavation. This is typically the fastest and most cost-effective approach for poured concrete cracks. For cracks that extend through the full wall depth and have compromised the exterior membrane — or where the crack is wider on the exterior face — we may recommend excavating to address it from both sides simultaneously: Duraflex membrane patch at the exterior, injection from the interior. We recommend the approach best suited to the specific crack rather than defaulting to one method for every situation.
Standard home insurance policies in Ontario typically do not cover foundation crack repair resulting from gradual deterioration, settlement, hydrostatic pressure, or chronic water intrusion — these are considered maintenance issues rather than sudden insurable events. Coverage may apply if cracking results from a sudden unexpected event such as an earthquake or a major sudden ground failure. Some overland water endorsements may cover interior water damage from a crack during a flooding event, but typically not the crack repair itself. We recommend contacting your insurer directly to review your specific policy. We can provide written documentation of the damage for insurance purposes if needed.
Interior polyurethane or epoxy injection for a single crack in poured concrete typically ranges from $500 to $1,500 depending on crack length and complexity. Multiple cracks, exterior membrane patching, carbon fibre strapping, or cracks requiring excavation will cost more. Every project is different — which is why we provide free written estimates before any work begins. You know exactly what you're committing to, with no surprises. Every crack repair includes a written workmanship warranty. Call (519) 278-5002 for a free on-site assessment.
Foundation cracks don't improve on their own. Freeze-thaw cycling widens them. Hydrostatic pressure forces more water through. The surrounding concrete deteriorates at the edges. The longer a crack stays open, the more it costs to repair — and the more damage accumulates in the meantime. Call us today for a free, no-obligation assessment.
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