Foundation cracks cause more homeowner anxiety than almost any other residential defect — and most of that anxiety is disproportionate to the actual risk. The vast majority of foundation cracks in Canadian homes are cosmetic or minor waterproofing issues, not structural failures. But some cracks are genuinely structural and require engineering assessment before any repair is done. Knowing which is which, and what to ask, is what separates an informed homeowner from one who pays for the wrong solution or misses a real problem.

“The crack that concerns me most isn’t the dramatic-looking one that runs diagonally across a poured concrete wall — that’s almost always a shrinkage crack and it’s typically cosmetic. The crack that concerns me is the horizontal one in a block wall that homeowners often dismiss because it looks small. Horizontal cracking in a block wall under significant batter indicates lateral soil pressure — that’s a structural issue that needs engineering assessment, not crack injection.”

— Patrick Osei, licensed structural engineer and foundation consultant with 22 years of experience in residential foundation assessment and waterproofing in the local area

Understanding Types of Cracks

High-resolution image of a cracked red-painted concrete wall surface for texture background.

What type of crack do I have?

Before asking any contractor anything, do your own initial assessment. The type of crack provides significant information about its cause and severity:

Vertical cracks in poured concrete:
The most common type. Usually caused by concrete shrinkage during curing or minor settlement. Generally not structural unless accompanied by displacement (one side higher than the other). Often amenable to crack injection as a waterproofing solution.

Diagonal cracks (stair-step in block, angled in poured):
Typically caused by differential settlement — one part of the foundation settling more than another. May be cosmetic if historic (not growing) and without displacement. May be structural if active (growing), with displacement, or if accompanied by visible movement in the structure above.

Horizontal cracks:
The most serious type. Horizontal cracking in a foundation wall indicates lateral pressure from the soil pushing against the wall. In block walls, this can indicate the wall is bowing inward under soil pressure — a structural failure mode that requires engineering assessment. In poured concrete, horizontal cracks may indicate similar lateral pressure issues.

Wall displacement (offset):
Any crack where one side of the wall is at a different elevation or position than the other indicates actual wall movement. This is a structural issue requiring engineering assessment.

Questions to Ask About Crack Assessment

Detailed texture of a weathered concrete wall showing crack patterns.

Is this crack structural or cosmetic — and how do you know?

Ask the contractor directly and ask them to explain their reasoning. A contractor who can explain the crack type, probable cause, and why they’ve concluded it’s structural (or not) is doing a real assessment. One who says “all foundation cracks need to be repaired” is selling, not diagnosing.

Red flag: Any contractor who recommends a major repair on a crack without being able to explain the structural distinction between crack types.

Is this crack active (growing) or historic?

An active crack is one that is currently moving — widening, shifting, or lengthening. A historic crack reached its final position years ago and hasn’t changed. Determining whether a crack is active is important for both the repair approach and the urgency.

A common method for monitoring cracks: apply tell-tale markers across the crack (a small line of plaster, or commercially available crack monitors) and photograph periodically. Ask the contractor whether they can confirm the crack is active or historic.

Does this crack require a structural engineering assessment?

Some cracks — horizontal cracks in block walls, cracks with significant displacement, or multiple cracks with a pattern suggesting systematic movement — require engineering assessment before any repair is done. A contractor who recommends crack injection on a crack that may indicate structural movement is potentially masking a serious problem.

Ask directly: does this crack require a structural engineer to assess before we repair it?

What a good answer looks like: A clear explanation of why this crack is or isn’t a structural concern, with a referral to a structural engineer if there’s any uncertainty.

For more: Do I Need a Structural Engineer for My Foundation Problem?

Questions About Crack Repair Methods

Is crack injection appropriate for this crack?

Crack injection — filling the crack with polyurethane foam or epoxy resin under pressure — is the appropriate repair for:

  • Vertical cracks in poured concrete that are non-structural
  • Diagonal cracks in poured concrete that are confirmed to be historic and non-structural
  • Cracks that are a localized source of water entry

Polyurethane injection: Creates a flexible, water-tight seal. Good for active (living) cracks that may continue to move slightly. The preferred option for waterproofing rather than structural purposes.

Epoxy injection: Creates a rigid, structural bond. Used when the crack needs to be structurally restored to full strength. Not appropriate for cracks that are still moving.

Ask the contractor which injection material is being proposed and why.

What crack injection is NOT appropriate for: Horizontal cracks indicating structural wall movement, active cracks in block walls, or any crack that hasn’t been assessed and confirmed to be non-structural.

What warranty does crack injection carry?

A properly injected crack should not re-open or re-seep. Ask what warranty the contractor provides on the injection work — both for the crack not leaking and for the repair not de-bonding.

What a good answer looks like: At least a one-year no-leak warranty on the injected crack, in writing.

For hollow-core block walls: is grouting appropriate?

Concrete block (CMU) foundation walls can be waterproofed by filling the hollow cores with concrete grout, combined with surface-applied waterproofing. This is a different approach than crack injection and appropriate for porous block walls that transmit water through the block rather than through specific cracks. Ask whether this approach is appropriate for your block wall type.

When to Get an Engineering Assessment

Get a structural engineering assessment before proceeding with any repair when:

  • The crack is horizontal in any wall type
  • There is visible displacement (one side higher than the other)
  • The crack runs through the full thickness of the wall (visible inside and outside)
  • Multiple cracks form a pattern suggesting systematic movement
  • There is visible wall bowing or deflection
  • The crack has appeared recently or is growing rapidly

An engineering assessment costs $500–$1,500 for a residential foundation. It is almost always worth it before a significant foundation repair.

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