Not every damaged slab needs to be torn out. The right fix depends on what is causing the problem, so a good repair starts with figuring out why the concrete cracked, sank or started to break down.
Common problems and their causes
- Hairline and shrinkage cracks: concrete shrinks slightly as it cures, and fine cracks are normal. They are mostly cosmetic.
- Wider or growing cracks: often caused by soil movement, tree roots, heavy loads or water getting under the slab.
- Sunken or tilted sections: the soil underneath has settled or washed out, leaving the slab without support.
- Heaving: soil that swells when wet can push slabs upward and break them.
- Flaking or crumbling surfaces (spalling): usually a sign of a weak surface, water damage or de-icing salts on older concrete.
Repair options
Crack sealing fills cracks with a flexible sealant or filler. It keeps water out from under the slab and slows further damage. It will not make a crack disappear, but it is inexpensive and worth doing early.
Slab lifting raises sunken sections back into place by pumping material underneath: either a cement-based slurry (often called mudjacking) or expanding polyurethane foam. It works when the slab is still in one piece and the soil underneath can be stabilized.
Resurfacing applies a thin bonded overlay to an old surface that is sound underneath but worn or flaking on top. It can freshen the look of a patio or walkway without a full replacement.
Partial replacement removes and repours only the damaged sections. Matching the color of old concrete exactly is difficult, so expect some visible difference.
Full replacement makes sense when a slab is broken in many places, heaving badly, or sitting on a failed base.
Fixing the cause
If water is running under the slab from a downspout or a low spot, or a tree root is lifting it, the same damage will return unless that is addressed. Ask the contractor what caused the problem and what they will do about it as part of the repair.
Questions worth asking
- What do you think caused this damage?
- Is repair a long-term fix here, or a stopgap until replacement?
- Will the repaired area match the rest of the slab?
- Is there anything about drainage or roots I should change?
Timing
Crack sealing and slab lifting are often done in a few hours, and the surface can usually be used the same day or the next. Partial and full replacements follow the same curing times as new concrete, so plan for about a week before driving on them.