Lifting and Leveling Sunken Concrete

Common scope

Drill, inject, raise, patch holes, seal joints

Best candidates

Whole panels that dropped and are still in one piece

Poor candidates

Broken, scaled-through or heaving panels

Key question

What caused the settling?

Why slabs sink around Wichita

Concrete sinks when the ground under it loses volume. Around Wichita, that usually comes from one of four things.

• Clay shrinking in drought. K-State Research and Extension explains that clay soils swell when wet and shrink as they dry, with enough force to move concrete sidewalks and crack foundations (K-State Research and Extension, Clay Soil: It Shrinks and Swells). After a dry summer, panels near the house or along a lawn edge can drop.
• Backfill settling. Soil placed against a foundation during construction often settles over the years, as K-State's basement guide notes (K-State Research and Extension, MF2809 Dry Basements and Crawl Spaces). Garage aprons, stoops and walks built over that fill sink with it.
• Water washing out the base. A downspout emptying at a slab edge, or a broken irrigation line, can carry fine soil away and leave a void.
• Poor original compaction. NRMCA lists improper subgrade preparation among the main causes of slab problems (NRMCA, CIP 4: Cracking Concrete Surfaces).

The Kansas Geological Survey calls expansive soils a pervasive problem in Kansas that heaves and shrinks season to season (Kansas Geological Survey, GeoRecord: geologic hazards and expansive soils). Lifting raises a slab; it does not change the soil. Fixing the water source that caused the void is part of any lasting repair.

Mudjacking versus foam

Cement-based grout (mudjacking)

A slurry of soil, sand, cement or similar material is pumped through holes drilled in the slab. The grout fills the void and, as pressure builds, lifts the panel. It is the older method, uses heavier material and typically needs larger holes. The added weight sits on the same soil that settled in the first place, which is worth discussing with the estimator.

Polyurethane foam

Two-part foam is injected through smaller holes and expands to fill voids and lift the slab. It is light and cures quickly. Because the material is different, the cost and the way it handles water differ too. Ask how each option would handle your soil and drainage.

When lifting is a good fit

• The panel is intact, or cracked in only one or two clean places.
• It settled as a unit, leaving a trip edge at a joint or a gap at the garage.
• The surface is otherwise in decent shape, without deep scaling.
• The water source that caused the settling can be fixed.

When it is not

• Heave, not settlement. If clay or a tree root has pushed a panel up, lifting the neighbors to match may not be wise. The high panel may need to come out.
• Shattered panels. A slab broken into many pieces will not lift as one.
• Badly scaled surfaces. Raising a crumbling slab leaves a level but still crumbling slab.
• Foundation movement. If cracks also show in the house walls, a foundation specialist should look first.

What happens after a lift

Drill holes are patched, and the joints around the lifted panel should be sealed so water does not wash out the new support. NRMCA's joint guidance stresses that joints accommodate movement and should be filled as specified (NRMCA, CIP 6: Joints in Concrete Slabs on Grade). Regrading so water drains away, and moving downspout outlets off the slab, help the lift last. K-State recommends ground that slopes away from a foundation, ideally about one inch for every foot over the first 15 feet (K-State Research and Extension, MF2809 Dry Basements and Crawl Spaces).

Questions worth asking before a lift

• Which panels will be lifted, and how far is each one expected to come up?
• What material goes underneath, and how many holes will be drilled?
• How will the holes and the joints be sealed afterward?
• What is the plan for the water source that caused the settling?

Lift, grind or replace?

A small trip edge on a walk can sometimes be ground flush. A sunken but intact driveway panel is a classic lifting job. A heaved, broken or scaled panel is usually a replacement. If the damage is mostly surface-deep, see repair and resurfacing. The clay soil guide explains why the same yard can sink one year and heave the next.

For what changes the scope of a lifting job, see the estimate factors page.

Sizing up the job: see what changes the size of a lifting job on the estimate-factors page. It lists what moves the scope, never a price.

Further reading

• Expansive Clay Soil and the Slabs That Sit on It
• Cracks, Joints and Heaving in Wichita Concrete
• Drainage Around Driveways and Patios