How to Level an Existing Concrete Slab

Assess the Slab and Choose a Leveling Method

Leveling an existing concrete slab is possible without tearing it out, and the right approach depends on the slab size, the severity of the unevenness, and the underlying cause. Small surface irregularities can be skim-coated with a polymer-modified overlay, while slabs that have settled due to soil erosion or compaction require lifting techniques. Before any work begins, walk the slab with a level or a straightedge to map the low spots and determine whether the issue is cosmetic or structural.

Prepare the Surface and Gather Materials

Clean the slab thoroughly with a pressure washer to remove dirt, grease, and loose debris, then let it dry. For mudjacking or foam injection, drill ⅝-inch holes through the concrete at strategic points near the low areas. Gather your leveling material—traditional mudjacking slurry, expanding polyurethane foam, or a self-leveling concrete overlay—along with a concrete mixer, pump, or pour pump, and protective gear including gloves, eye protection, and a dust mask.

Mudjacking (Slabjacking)

Mudjacking pumps a mixture of water, soil, sand, and cement under the slab through the drilled holes. The slurry fills voids and lifts the concrete back into position. This method is cost-effective for larger slabs and works well when the subgrade has settled but remains stable.

Polyurethane Foam Injection

Polyurethane foam expands after injection, lifting the slab with minimal disruption. It cures quickly, weighs far less than mudjacking slurry, and resists water erosion, making it a popular choice for both residential and commercial applications.

Self-Leveling Overlay

For slabs that are structurally sound but have minor surface unevenness, a polymer-modified self-leveling overlay can be poured to create a smooth, flat finish. This method does not address settlement but effectively corrects trip hazards and prepares the surface for new flooring.

Execute the Leveling Work

For mudjacking or foam injection, insert the injection ports into the drilled holes and pump the material until the slab rises evenly. Monitor the process closely; over-lifting can crack the slab or create new high spots. Once the slab is level, plug the holes with concrete patching compound and allow the repair material to cure fully before applying any loads or finishes.

Prevent Future Settlement

Address the root cause of the unevenness by improving drainage around the slab, filling any underlying voids, and compacting the subgrade where possible. Proper grading and gutter maintenance reduce the water erosion that causes most concrete settling.