Short answer
Concrete can often be repaired when damage is limited to the surface or to a few cracks over a sound base. When the slab has settled, heaved or scaled across large areas, resurfacing is usually a short-term cosmetic fix and replacement is the honest answer. A contractor should explain why before quoting.
Repair, resurface or replace: how to decide
| What you see | Likely cause | Usual approach |
|---|---|---|
| Hairline surface cracks | Shrinkage or normal movement | Often left alone, or sealed to keep water out. |
| Wider cracks, same height both sides | Movement, loading or drainage | Rout and fill with flexible sealant; monitor. |
| Crack with one side higher or lower | Base settlement or frost heave | Slab lifting or replacement, after finding the cause. |
| Surface flaking or scaling | Freeze-thaw with salt on non-air-entrained or unsealed concrete | Resurfacing overlay if the slab is sound; replacement if widespread. |
| Exposed stone or deep pitting (spalling) | Repeated freeze-thaw damage or reinforcement corrosion | Patch small areas; replace if extensive. |
| Crumbling edges or corners | Water and salt at edges, poor support | Edge repair or partial replacement. |
| Slab pools water | Settled or poorly sloped slab | Slab lifting or regrading; replacement if drainage cannot be fixed. |
If more than a small portion of the surface is failing, or the base has moved, repairs tend to fail again within a few winters. See concrete driveways for the replacement route.
Repair methods explained
- Crack filling and sealing. Flexible sealants keep water out of cracks. They do not restore strength and need periodic renewal.
- Patching. Damaged areas are cut back to sound concrete and filled with a repair mortar. Patches may remain visible.
- Resurfacing or overlays. A thin bonded layer is applied over a sound slab to renew the surface. It does not fix settlement or a failed base.
- Slab lifting. Some contractors raise settled slabs by injecting material beneath them. This works only if the cause of settlement is fixed and the slab is otherwise sound.
- Sealing. A good sealer slows water and salt absorption and is the cheapest way to extend the life of sound concrete.
- Replacement. When the base, drainage or the slab itself has failed, replacement is the only lasting fix.
Not every concrete contractor offers every method, so ask which they do and what experience they have with each.
Why concrete fails in southern Ontario
Most repairable damage in London is from freeze-thaw cycles combined with de-icing salts, especially on concrete that was not air-entrained, was finished too wet or was never sealed. Read the salt and frost damage guide to understand the causes and what you can do to slow them.
Settlement and heave come from poor base preparation, drainage that sends water under the slab and frost action in clay or wet soil. Those are base problems, so surface repairs alone will not solve them.
What repair work costs
We have not found a reliable published Ontario price range for repair and resurfacing, so we are not quoting one. Prices vary widely with the type and extent of damage and the method used. The same Ontario guide used elsewhere on this site (HomeStars, August 2026, Ottawa-based) lists demolition at about $3 to $8 per square foot and slabs at about $3.80 to $5 per square foot, which gives a rough sense of the replacement option for comparison only. Ask for written quotes for both repair and replacement so you can compare.
Questions to ask before you repair
- What caused the damage, and will the repair address the cause?
- How long do you expect the repair to last, and what does the warranty cover?
- Will the repair match the surrounding concrete?
- What happens if the damage returns?
- Do you carry liability insurance and a current WSIB clearance certificate?
- Would you recommend replacement in my case, and why or why not?
Frequently asked questions
Can cracked concrete be repaired?
Often yes, if the base is sound and the crack is not widening. Flexible sealants keep water out, but they do not fix the cause of movement.
Is resurfacing worth it?
It can be for a sound slab with surface scaling. It is not a fix for settlement or widespread cracking.
Why is my driveway flaking?
Usually freeze-thaw damage to the surface, made worse by de-icing salts, and often related to the mix, finishing or lack of sealing.
How long does a repair last?
It depends on the cause and the method. Surface repairs over an unstable base tend to fail again. Ask for a written warranty.
Can you lift a sunken slab?
Some contractors can, but the cause of settlement must be addressed first. Ask about the method and what is guaranteed.
Do I need to seal concrete after repair?
Sealing is generally recommended once the repair has cured, to reduce water and salt absorption.