Garage Foundation Repair Edmonton: Repair or Replace?

Reading time: 8 minutes

Standing in your Edmonton garage, looking at a cracked and tilted slab, most homeowners ask two questions. First: why is it doing this? Second: do I have to replace the whole thing?

The answers are related. Your garage floor is cracking because of frost. Edmonton’s soil freezes to 2.4 metres depth every winter, and your garage slab, sitting on unheated soil that freezes and thaws with the air, is moving with it. In most cases, you do not need to replace the slab. You need to address what is happening underneath it.

A garage settling away from the house is a common headache, and the methods we use mirror the same foundation repair work for Edmonton homes across the city. Here is how a garage foundation gets diagnosed and brought back to level.

Why Edmonton Garage Foundations Fail Differently

Your house basement and your garage floor sit in Edmonton’s clay soil, but they respond to winter very differently. The reason is heat.

Your heated house basement maintains a relatively stable soil temperature beneath its footings. Interior warmth conducts downward, significantly limiting how deep frost penetrates beneath the structure. An unheated garage offers no such protection. The soil beneath your garage slab freezes right along with the outdoor temperature. An attached garage that is cold but enclosed might be -20 to -25°C on a January night in Edmonton. That slab and the soil beneath it are frozen solid.

Edmonton averages approximately 91 freeze-thaw cycles per year (air temperature crossings of 0°C). A heated house basement soil experiences a small fraction of those cycles. An unheated garage slab soil experiences nearly all of them. Over 30 years in Edmonton, that adds up to over 2,700 freeze-thaw events working on your garage subgrade.

A second factor compounds frost heave: differential settlement from vehicle loads. A 2-tonne SUV parked in the same two tire contact zones day after day compresses and consolidates the soil beneath those spots. Meanwhile, adjacent areas may be heaving. The result is an uneven slab with cracking at the transition zones between moving and stationary areas.

Common Edmonton Garage Foundation Problems

The same frost and clay conditions produce the same patterns of damage across Edmonton garages. Here are the most common, in order of frequency:

• Slab cracking and heaving: Diagonal, transverse, and longitudinal cracks from frost heave and differential settlement. The perimeter of the slab typically heaves more than the centre, producing a raised outer edge and a lower central zone with cracking at the boundary between them.
• Gap at the garage door threshold: The interior slab and the exterior apron are separate concrete pours. They move independently. The interior slab heaves from frost below, or the exterior apron sinks as voids form beneath it, or both happen simultaneously. The result is a raised lip or a step at the door threshold that is both a trip hazard and a drainage problem.
• Corner cracks at the overhead door opening: The garage door opening is the structurally weakest point in the perimeter wall. Temperature differentials concentrate here. Diagonal cracks running from the upper corners of the door opening are extremely common in Edmonton garages.
• Separation between the house and garage walls: Attached garages have their own independent foundation that moves more than the house foundation. The joint between the house exterior wall and the garage wall opens over time, allowing water, air, and pest infiltration.
• Sloped floor draining toward the back wall: A garage floor that was level when poured but has heaved at the front (near the door) now slopes toward the back. Standing water accumulates near the back wall in spring, freezes in winter, and accelerates damage to both the slab and anything stored there.

Repair or Replace? The Cost Comparison

This is the question most Edmonton homeowners need answered before they call anyone. Here is the honest comparison:

The math is clear when the slab is structurally sound. A garage slab that has heaved 2 inches but is not spalling or severely deteriorated is a polyjacking candidate. You do not need to demolish and replace it. You need to fill the voids, compact the loose soil, and lift it back to level.

The critical qualifier is “structurally sound.” A slab that is cracked is not automatically unsound. Polyjacking can lift and stabilise a cracked slab. The individual sections are lifted together and the filled subgrade holds them in position. What determines whether replacement is necessary is the condition of the concrete itself: depth of spalling, rebar integrity, and whether the slab can function as a structural unit.

How Polyjacking Works

Polyjacking uses high-density polyurethane foam injected beneath the slab to fill voids, compact the loose subgrade, and lift the concrete back to its target elevation. Here is the process step by step.

Step 1: On-site inspection to identify the cause. Before any drilling, Tim inspects the garage slab on site to read why it is moving. He checks the crack patterns, the slope, the threshold lip, and the drainage around the structure to work out where the voids and soft soil are and whether frost heave, settlement, or water is driving the problem. This step determines where injection holes go and how much foam will be needed. Injecting without understanding the cause is guesswork. With a proper inspection, the injection plan is based on what is actually happening below. Learn more in our guide on foundation repair in Edmonton.

Step 2: Drilling the injection holes. Small holes, 5/8 inch in diameter, are drilled through the slab at the locations identified during the inspection. These holes are spaced to target void zones and soil compaction areas. Their small size means the surface patch is nearly invisible after completion.

Step 3: Foam injection and lift. The two-component foam is injected under the slab in controlled increments. As the foam expands, it fills voids, compacts loose soil, and exerts gentle upward pressure that lifts the slab. The elevation is monitored continuously. Injection pauses frequently to allow the foam to stabilise and the lift to be measured before adding more.

Step 4: Hole patching. Once the slab reaches its target elevation, the injection holes are patched with a matching concrete mix. The surface is clean and essentially invisible from normal viewing distance within minutes.

Step 5: Ready for use. Foot traffic within 15 to 20 minutes. Vehicle loads the same day.

When Slab Replacement Is Actually Necessary

Polyjacking is not always the right answer. Replacement is the correct choice when:

• The concrete itself is severely deteriorated throughout. Spalling deeper than one inch across large sections, exposed and actively corroding rebar, delamination of the surface aggregate. When the concrete matrix is compromised, lifting it just lifts a crumbling surface.
• The slab has fractured into many small, displaced pieces. Polyjacking lifts sections. If the slab has shattered into dozens of fragments that cannot be lifted as units, injection cannot restore a flat, functional surface.
• Salt-related concrete failure has penetrated through the full slab depth. Fifteen years of winter vehicles tracking salt brine onto a bare, unsealed concrete floor can cause chloride-induced corrosion that reaches the rebar and causes internal concrete fracture from the inside out. When this has progressed throughout the slab, replacement is the only option.
• The heave or settlement is so severe that the slab cannot be lifted as a unit. Displacement of more than 6 to 8 inches in some zones while other zones are still low is difficult to correct without replacement of the most severely displaced sections.

The honest assessment is that replacement is necessary in roughly 20 to 30 percent of Edmonton garage slab situations Tim encounters. In the remaining 70 to 80 percent, polyjacking delivers the same result at a fraction of the cost.

Edmonton-Specific Factors: Salt, Clay, and Cycle Count

Three Edmonton-specific realities accelerate garage foundation damage beyond what you’d see in a milder Canadian city.

Road salt and chloride attack. Edmonton applies road salt from November through March. Every vehicle that parks in your garage brings salt brine on its tires and undercarriage. On bare concrete, this brine penetrates the porous surface and reaches the concrete matrix. Calcium chloride reacts with calcium hydroxide in concrete to form calcium oxychloride, which expands inside the concrete and causes internal fracture. Combined with freeze-thaw cycling of salt-saturated concrete, this is an accelerant that produces the pitting and spalling surface common in older Edmonton garage floors. An epoxy or polyurea floor coating applied after polyjacking addresses this: it seals the concrete surface against brine infiltration and makes cleaning easier.

Edmonton glacial till clay. The soil beneath Edmonton garages is primarily glacial till clay: a fine-grained, frost-susceptible soil that swells up to 20% when saturated and contracts when dry. Both movements stress the slab from below. For more on Edmonton’s clay soil behaviour, see our guide on Edmonton clay soil and your foundation.

91 freeze-thaw cycles per year. An unheated garage slab in Edmonton experiences nearly all 91 average annual freeze-thaw cycles directly. Each cycle that produces soil movement adds to the cumulative damage. Over 30 years, the subgrade beneath a 1980s Edmonton garage has experienced over 2,700 cycles of movement. The cracked floor you are standing on is the result of that history.

Get a Garage Foundation Assessment in Edmonton

If your garage floor is cracked, heaved, or has a lip at the threshold, the first step is understanding what is happening beneath the slab. Polyjacking solves the problem in most cases, at a cost that is a fraction of replacement. But the right repair starts with accurate information about what is underground.

Alberta Foundation Repair serves Edmonton and surrounding areas: (519) 732-1964

Tim inspects every garage on site and identifies the cause before recommending or starting any repair. You understand why the slab is moving before anyone drills a hole. No guesswork, no over-injecting, no unnecessary replacement.