A crack in your foundation wall is not automatically cause for alarm, but it's never something to ignore. The significance of a crack depends entirely on its type, orientation, width, and whether it's stable or actively changing. Getting a proper diagnosis before committing to a repair approach saves Ottawa homeowners from spending money on solutions that don't address the actual problem.
Understanding Foundation Crack Types
Vertical Cracks
Vertical cracks are the most common type in poured concrete foundations and are typically caused by concrete shrinkage during the curing process. Shrinkage cracks form within the first few years of a home's life, are usually uniform in width from top to bottom, and are generally stable, meaning they don't widen significantly over time.
Shrinkage cracks are not structural concerns but they are water pathways. A vertical crack 1–2mm wide in a poured concrete wall, with no lateral displacement, can typically be repaired by low-pressure polyurethane foam injection, an effective, minimally invasive technique that seals the crack from the inside.
Horizontal Cracks
Horizontal cracks in a concrete block or poured concrete foundation wall are a more serious finding. They typically indicate lateral pressure from soil or frost pushing against the wall. If the crack is accompanied by inward bowing of the wall, that's a structural emergency that needs professional assessment immediately.
Do not ignore a horizontal crack that is widening or where the wall face has displaced inward, even by a few millimetres. These cracks require structural remediation, not just waterproofing.
Diagonal or Stair-Step Cracks
Diagonal cracks in poured concrete walls, or stair-step cracks following the mortar joints in block walls, often indicate differential settlement, one part of the foundation moving independently of another. In Ottawa, this can result from frost heave, inconsistent soil conditions, or tree root pressure.
Minor diagonal cracks (hairline, stable, no displacement) can often be injected and sealed. Cracks with visible lateral or vertical displacement, or cracks that are actively growing, indicate an ongoing movement problem that needs to be addressed at the source, not just sealed at the surface.
The Right Repair for Each Situation
Crack Injection (Low-Pressure Polyurethane or Epoxy)
Polyurethane foam injection is the standard approach for sealing non-structural vertical cracks in poured concrete foundations. The foam is injected at low pressure, expands to fill the full depth of the crack, and cures to a flexible solid that accommodates minor future movement. It's done from the interior, with no excavation required.
Epoxy injection is used when structural restoration of the crack is needed, it bonds both faces of the crack together and restores tensile strength. Epoxy is less flexible than polyurethane and is not appropriate for cracks that may experience future movement.
Exterior Membrane Waterproofing
When a foundation wall has multiple cracks, widespread moisture penetration through the wall face, or where the existing damp-proofing membrane (applied at original construction) has failed, exterior waterproofing is the comprehensive solution. This involves:
- Excavating to the footing on the affected wall section(s)
- Cleaning and preparing the wall face
- Applying a new waterproofing membrane (rubberized asphalt or spray-applied polymer)
- Installing drainage board to protect the membrane and direct water downward
- Re-grading and compacting backfill with appropriate drainage aggregate
Exterior waterproofing is the most effective and lasting solution for water penetration through foundation walls, it stops water at the exterior face rather than managing it after it enters. It is also the most disruptive and expensive option, requiring excavation along the home's perimeter.
Interior drain tile systems (sometimes marketed as "waterproofing") are a water management system, not a waterproofing solution. They collect water that has already entered the wall and direct it to a sump pump. They're a legitimate solution in some situations, particularly where exterior excavation isn't feasible, but they don't stop water penetration. We offer exterior waterproofing, which does.
What Causes Foundation Water Problems in Ottawa
Most foundation water problems in Ottawa homes trace to one or more of the following:
- Grading: Soil that slopes toward the foundation directs surface water against the wall. Even modest negative grading can cause significant water accumulation at the base of the wall.
- Eavestroughs and downspouts: Disconnected, blocked, or poorly directed downspouts concentrate enormous volumes of roof runoff directly at the foundation.
- Failed or blocked weeping tile: The perimeter drainage tile installed at original construction gradually fills with silt and roots over decades. When it stops draining effectively, ground water that used to be directed away now builds up against the wall.
- Failed original damp-proofing: Most homes built before the 1990s were damp-proofed rather than waterproofed, a thin bituminous coating applied to the exterior wall that degrades over time. This is not waterproofing and often fails well before the 40–50 year life of the home.
When to Call a Masonry Contractor vs. a Structural Engineer
Call a masonry contractor for: vertical crack injection, failed parging repair, exterior membrane waterproofing of non-structural walls, and repointing of block foundation walls.
Call a structural engineer first if: you see horizontal cracking in a foundation wall, the wall is visibly bowing inward, you have wide (5mm+) diagonal cracks with displacement, or the crack is growing rapidly. A structural assessment should precede any waterproofing work when structural movement is suspected.
Foundation Concerns in Ottawa?
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