Concrete Slab Leveling Guide

Three approaches address settled concrete slabs. Mudjacking (slab jacking): a cement-based grout is mixed and pumped under pressure through ½-inch to 2-inch holes drilled in the slab. The grout fills voids and lifts the slab as it fills. Mudjacking is proven, cost-effective ($3–$6 per square foot), and appropriate for large areas like driveways and sidewalks. Polyurethane foam leveling: a two-part expanding foam is injected through small holes (18-inch spacing). The foam expands in seconds, filling voids and lifting the slab precisely. Curing time is 15 minutes, making it ideal for areas needing quick return to service. Cost: $5–$10 per square foot. Full replacement: removing and repouring the concrete is the most expensive option ($8–$15 per square foot) but allows for modern reinforcement and proper base preparation. Replacement is needed only when the slab is severely cracked or broken.

Not every uneven slab needs leveling. Level when: the slab has settled more than ½ inch, water pools on the surface, a trip hazard exists (rise over ¼ inch), or doors and entryways are affected by the movement. Replace when: the slab has multiple cracks wider than ¼ inch, the concrete is spalling or crumbling (indicating freeze-thaw damage or poor concrete mix), the slab has heaved upward (requires removal to address the cause), or the slab is at least 50% cracked. Leveling is not recommended for slabs with active water problems—the water source must be addressed first or the slab will continue to settle. For slabs under 50 square feet, replacement may be comparable in cost to leveling. For large areas (over 200 sq ft), leveling is significantly more economical than replacement.

Professional concrete leveling follows a defined process. 1. Drilling: ½-inch to 2-inch diameter holes are drilled through the concrete slab at strategic locations (typically 2–4 feet apart along the settled area). 2. Injection: grout or foam is pumped through the holes starting at the lowest settling point, working outward. 3. Lifting: the material fills underground voids, then begins to lift the slab. The contractor monitors lift using a level and stops when the slab reaches the target elevation. 4. Hole patching: injection holes are patched with concrete patch or plug (the patch color matches the surrounding concrete). 5. Cleanup: equipment is rinsed, and the area is swept. The entire process for a typical 10×10 area takes 2–4 hours for mudjacking and 1–2 hours for foam. Most contractors offer same-day service for foam leveling (driveable within 1 hour) vs. 24-hour cure for mudjacking.

Slab settling is almost always caused by water—either erosion of soil from under the slab, or soil shrinkage from drought. If you level a slab without fixing the drainage problem, it will settle again. Before leveling, ensure: downspouts discharge at least 5 feet from the slab, the ground slopes away from the slab at 5%, and no irrigation spray directly hits the slab edge. For slabs on expansive clay soils, maintain consistent soil moisture around the slab perimeter. If tree roots are causing soil shrinkage, consider a root barrier. A good contractor will include drainage recommendations with the leveling quote. Spending $100–$200 on drainage improvements extends leveling results from 3–5 years to 10+ years. Never level a slab without first addressing what caused it to settle.

Sidewalk leveling (4×4 section): mudjack $50–$100, foam $75–$150, replace $200–$400. Driveway leveling (400 sq ft at apron): mudjack $1,200–$2,400, foam $2,000–$4,000, replace $3,200–$6,000. Patio leveling (10×10): mudjack $300–$600, foam $500–$1,000, replace $800–$1,500. Garage floor leveling (250 sq ft): mudjack $750–$1,500, foam $1,250–$2,500, replace $2,000–$3,750. Interior slab leveling (basement floor): foam only (mudjack grout is too heavy and may cause further settling), $800–$2,000. These estimates include labor and materials. Most contractors offer fair quotes and will recommend the best method for your specific project. Check with your insurance company—some policies cover slab leveling if caused by a covered peril (burst pipe under slab).