Foundation crack repair — Montreal, Laval & the Laurentians
A crack in your foundation wall or slab should never be taken lightly. Drain MPR evaluates the type, cause, and severity before choosing the appropriate repair method — from the inside or the outside, for both residential and commercial properties.
A crack is an entry point for water
Quebec's foundations are subjected to intense freeze-thaw cycles, hydrostatic pressure, and clay soil movements. Not all resulting cracks are urgent, but none should be ignored. Concrete contracts as it dries, clay soils exert lateral pressure, and repeated cycles progressively fatigue the structure. Most cracks remain repairable without major work — provided you intervene before they worsen. A fine crack that lets moisture through can, within a few years, become an active infiltration that damages insulation and degrades the structure. Furthermore, the connection with drainage is close: a failing French drain increases hydrostatic pressure around the foundations, accelerating the appearance and widening of cracks.
Main types of foundation cracks
The shape and orientation of a crack reveal a lot about its cause and severity. Here are the most common types in properties across Montreal, Laval and the Laurentians.
Fine Vertical Crack
The most common, often caused by concrete shrinkage during drying. As long as it remains fine (less than 1 mm), stable, and dry, it poses no structural risk. If it lets moisture through or widens, an injection is recommended.
Diagonal Crack
It extends diagonally from the corner of a window or door and generally indicates foundation movement — localized settlement or asymmetric freeze-thaw. Evaluating the cause is essential before repair.
Horizontal Crack
The most concerning type. It often results from lateral soil pressure exceeding the wall's capacity — a situation that can lead to displacement if left untreated. A structural consultation is essential.
Slab Crack
Frequent, it stems from concrete shrinkage, excessive loading, or poorly compacted soil. If fine and stable, it is of little concern. If wide, with vertical offset or moisture, it warrants intervention against rising damp.
Slab-Wall Joint Crack
Often the primary basement infiltration point: water accumulated under the slab via hydrostatic pressure naturally finds this path. A polyurethane injection seals the joint, but a French drain in good condition remains the best long-term protection.
Diagnosis first, treatment second
Filling a crack without understanding its cause is treating the symptom rather than the problem. If soil pressure, poor drainage, or structural movement is to blame, the crack will reappear. Drain MPR always begins with a thorough examination before recommending a treatment — here is what we look at:
Orientation and Profile
Vertical, horizontal, or diagonal: each orientation indicates a different cause and a distinct level of structural risk.
Width and Depth
A crack of less than one millimeter is generally benign. Beyond 3 mm, a structural evaluation is required.
Presence of Moisture
Dry, damp, or active crack: each state determines the most appropriate injection product.
Evolution Over Time
A crack that progressively widens signals an active problem — soil movement or continuous pressure — that must be addressed as a priority.
Signs that warrant a prompt evaluation
Some cracks can wait, others justify an immediate call. Here are the signs to monitor closely.
Moisture or Active Infiltration
Water seeping through a crack during heavy rain or snowmelt reveals a through-crack. Each rain event worsens the internal erosion of the concrete.
Crack Wider Than 3 mm
Beyond 3 mm wide, a crack goes beyond simple concrete shrinkage. A structural evaluation is necessary to determine if the foundation is compromised.
Widening Crack
If a crack has grown since your last inspection (compare with a dated photo), it is a sign of an active problem — moving soil, increasing pressure — requiring intervention.
Horizontal Crack
A horizontal crack on a foundation wall signals lateral pressure potentially exceeding the wall's capacity. This is the most serious type of crack and requires priority assessment.
Mold near a crack
Mold near a crack confirms that moisture is regularly seeping in, even if not continuously visible. Intermittent moisture can be as damaging as continuous moisture.
Sticking Doors or Windows
Doors or windows that suddenly stick for no apparent reason can indicate foundation movement — often linked to settlement or soil pressure that also causes cracks.
Repair from the inside or the outside
The choice of method depends on the crack type, its cause, accessibility, and your situation. Drain MPR recommends the tailored method after diagnosis — not a one-size-fits-all solution.
Epoxy or polyurethane injection
he least invasive method: the technician drills ports along the crack and injects the product under pressure, which penetrates to the outer surface of the wall. No digging required. Epoxy bonds dry cracks, while polyurethane creates a watertight seal on wet or active cracks. Work takes a few hours, ideal for accessible vertical and diagonal cracks.
Exterior Repair & Waterproofing
Partial excavation right at the crack gives access to the wall from the outside. The crack is cleaned, repaired, and a waterproofing membrane is applied across the entire surface. The most durable solution for deep cracks caused by hydrostatic pressure — it treats the cause at the source and can be combined with the installation of a French drain.
Epoxy — Dry Cracks
Epoxy injection bonds both sides of the crack and restores the structural strength of the concrete. This is the indicated choice when the crack is dry during the intervention.
Polyurethane — Active Cracks
Polyurethane injection swells upon contact with water to create a flexible watertight seal. It is the suitable solution for wet or active cracks that let water through during the work.
WHAT AN IGNORED CRACK CAN LEAD TO
Fixing a minor crack early is a simple repair. Ignored, it opens the door to a chain reaction of damage
Mold and contamination
Chronic humidity creates ideal conditions for mold. A contaminated basement requires costly remediation and can affect indoor air quality throughout the house.
Structural Deterioration
Water freezing and thawing inside a crack progressively widens it. What could be patched by injection might require partial wall reconstruction a few years later.
Impact on Property Value
A damaged foundation is one of the first things a building inspector flags during a sale. Untreated cracks can delay or compromise a transaction.
Compromised Insulation
Infiltrating moisture saturates basement insulation and reduces its thermal efficiency. Result: a colder house and higher heating bills in winter.
Progressive Worsening
Cracks do not disappear on their own. Without intervention, every Quebec freeze-thaw cycle enlarges them further, and repairs become more complex over time.
Insurance Due Diligence
Acting quickly documents your maintenance diligence. A dated diagnostic report supports your claim with the insurer if a claim becomes necessary later.
Our repair process
From diagnosis to repair, here's how Drain MPR tackles every crack — with a methodical, unhurried approach.
On-Site Evaluatio
Complete visual inspection of the crack (orientation, width, depth, moisture, evolution) and examination of the context: drainage, terrain, property history.
Diagnosis & Recommendation
Identification of the probable cause and recommendation of the appropriate method — interior injection, exterior repair, or a combination of both.
Targeted Repair
Execution of the work according to the selected method — epoxy or polyurethane injection, or partial excavation with a waterproofing membrane — adhering to industry standards.
Additional Recommendations
If the cause is linked to drainage (failing French drain, hydrostatic pressure), we recommend complementary measures to prevent recurrence.
CRACKS & DRAINAGE: A DIRECT LINK
- 1
Hydrostatic Pressure Accumulates
When the French drain no longer does its job, water stagnates against foundation walls and exerts continuous pressure. This pressure pushes water toward the weakest points of the concrete.
- 2
Water Finds Existing Cracks
Pressure seeks the path of least resistance: pre-existing cracks widen, and new weak points may yield in turn.
- 3
Patching Alone Is Not Enough
Repairing a crack without fixing the drainage often just delays the problem by a few years. The crack reappears, sometimes elsewhere on the same wall.
- 4
A Comprehensive Approach
Drain MPR treats the crack and evaluates the drainage in the same process — ensuring the repair lasts sustainably.
Throughout Montreal, Laval & the Laurentians
Based locally, Drain MPR evaluates and repairs foundation cracks in the following municipalities:
FAQ — Cracks repair
Are all foundation cracks dangerous?
Is it better to repair a crack from the inside or the outside?
What is the difference between epoxy and polyurethane injection?
Can a repaired crack reopen?
What is the relationship between foundation cracks and drainage?
Does my insurance cover foundation crack repair?
Additional services
Une fissure dans la fondation est rarement isolée — elle est souvent le symptôme d’un problème de drainage. Voici les services qui y sont directement liés.
A crack in your foundation? We start with the diagnosis.
The longer you wait, the more complex the repair becomes. Our team evaluates the cause in Montreal, Laval and the Laurentians, then recommends the appropriate method. Free diagnosis and quote, or call directly.
