Concrete walkway heaving or settling unevenly

Symptoms

• One slab noticeably higher or lower than its neighbor
• Trip hazard at a slab joint
• Cracking concentrated at the raised or sunken edge

Likely causes

• CommonFrost heave lifting a slab in winterWater in the soil beneath a slab freezes and expands, pushing that section upward, sometimes settling back only partially in spring.
• CommonTree roots growing under a slabRoots can lift a slab as they grow beneath it over years.
• PossibleSoil erosion or settling under a slabPoor compaction or water erosion can leave a void that a slab eventually sinks into.

What to do

1. Measure the height difference between slabs to assess the trip hazard severity.
2. As a temporary safety fix, add a beveled asphalt or rubber trip-hazard ramp at the offset joint.
3. Identify whether a visible tree root is the cause, and consult an arborist before cutting a large root, which could harm the tree or destabilize it further.
4. For a sunken slab, mudjacking or polyurethane foam injection can lift it back to level without full replacement.
5. For a badly cracked or heavily lifted slab, replacement may be more practical than lifting.
6. Address any drainage issue contributing to soil erosion under the walkway.
7. Recheck the repaired area after the next winter to confirm it has stabilized.

Tools and parts

• Tape measure
• Level

When to call a pro

Call a concrete contractor for mudjacking, foam leveling, or slab replacement.

Safety