Damaged concrete in the Twin Cities can often be lifted with cement slurry or polyurethane foam, sealed, patched or resurfaced. Common causes are freeze-thaw scaling, frost heave, settling fill and washouts. Because slabs can move with frost, many contractors evaluate lifting after the ground thaws, and any repair should fix drainage too.
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Not every damaged slab in Minneapolis or St. Paul needs to be torn out. Depending on the cause, concrete can often be lifted, sealed, patched or resurfaced for less cost and disruption than a full replacement. The key is figuring out why it failed, because a repair that ignores the cause tends to fail again after the next winter.
Why concrete fails in the Twin Cities
- Freeze-thaw scaling. Water in the surface freezes and expands over and over, and salt makes it worse. The result is flaking, pitting and exposed stone, often worst near the garage and front door.
- Frost heave. Water held in clay-rich soil under a slab can freeze and lift panels in winter, then let them settle unevenly in spring.
- Settling fill. Backfill next to foundations, garages and steps can compress over the years and leave slabs tipping toward the house.
- Washouts. Downspouts and spring snowmelt can carry soil out from under slab edges, especially in sandier soils.
- Tree roots. Mature boulevard and yard trees lift walks and driveway edges.
- Shrinkage. Some cracking is normal as concrete dries, especially where joints are too far apart.
Repair options
- Slab lifting (mudjacking): a cement-based slurry is pumped under a sunken slab through drilled holes to raise it and fill voids.
- Polyurethane foam lifting: an expanding foam is injected through smaller holes. It's lightweight and cures quickly.
- Crack and joint sealing: flexible sealants keep water out of cracks and joints, which matters a lot where that water would otherwise freeze.
- Patching: spalled spots can be patched with repair mortars, though patches rarely match.
- Resurfacing: a thin cement-based overlay can renew a scaled surface on a slab that is otherwise sound and stable.
- Section replacement: badly broken or scaled panels are cut out at joints and repoured.
Timing repairs around frost
A slab that's heaved in February may settle back by May. Many contractors prefer to evaluate lifting after the ground thaws, so they're working with the slab's true resting position. Crack sealing and many overlays also need temperatures above certain minimums to cure, which usually means the warmer months. If a panel has become a trip hazard in winter, mark it and keep it clear of ice until it can be fixed.
When lifting makes sense
Lifting usually works best when the slab is mostly intact, has sunk as a unit, and the soil underneath has stopped moving. A slab that rises and falls with frost every year may keep doing so unless drainage is improved. Badly broken or deeply scaled slabs are often better replaced. Extending downspouts and regrading should be part of the plan either way.
Trip hazards and public sidewalks
An uneven joint is a common cause of falls. Contractors can lift the low side, grind the high edge, or replace the panel. If the hazard is on a public sidewalk, check with your city first. Minneapolis bills adjacent owners for sidewalk repairs it identifies, while St. Paul maintains its mainline sidewalks, and both require a city-licensed contractor for right-of-way work.
When it might be structural
Cracks in a garage floor or patio are usually not structural. Cracks in foundation walls, a basement floor that's heaving, or doors and windows that suddenly stick can signal foundation movement. In those cases, an evaluation by a structural engineer or foundation specialist is the right first step.
Questions to ask
- What caused the problem, and how will the repair address it?
- Will you lift, resurface or replace, and why?
- Is there a warranty if lifted slabs settle or heave again?
Not sure which way to go? Read our guide to winter damage, then request a concrete repair contractor and mark it urgent if it's a trip hazard.
See how it works
Frequently asked questions
Should I fix a heaved slab in winter or wait for spring?
Frost-heaved slabs often settle back after the thaw, so many contractors evaluate lifting or replacement once the ground has thawed. In the meantime, mark trip hazards and keep them clear of ice.
Is mudjacking or foam lifting better?
Both can lift sunken slabs. Cement slurry is long established; polyurethane foam uses smaller holes, is lighter and cures quickly. The right choice depends on the slab, the voids and the soil.
Can a salt-scaled driveway be resurfaced?
If the slab is structurally sound and not moving, a cement-based overlay can often renew the surface. If scaling is deep or widespread, or the slab is cracked and shifting, replacement is usually the better value.
Sources and further reading
- American Concrete Institute (ACI)
- Portland Cement Association (PCA)
- Minnesota Department of Labor and Industry: residential contractor licensing
- City of Minneapolis: curb cuts for residential properties
- City of Minneapolis: city sidewalk repair process
- City of Saint Paul Public Works: sidewalks
- City of Saint Paul: sidewalk contractor license
- City of Bloomington: residential driveway approaches and curb cuts handout
- Minnesota Rules chapter 1303 (frost depth zones), Office of the Revisor of Statutes
- Hennepin County landslide atlas: Minnesota River valley
- Minnesota Pollution Control Agency (winter salt and chloride)
- Gopher State One Call (Minnesota 811)
- Minnesota Department of Public Safety: Gopher State One Call