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A slab foundation is a concrete slab at ground level. It carries the house load and serves as the floor. When soil under a slab moves unevenly, the slab cracks, slopes or lifts in places. This page explains slab repair in plain words.
What the job is
Slab repair restores support under a slab, reduces further movement and, where possible, returns the slab toward level. Work may include piers, underpinning, void filling, crack sealing and drainage correction. The exact job depends on whether the slab has settled, heaved or both.
Heaving means soil pushes a slab up. Settlement means soil drops and a slab falls. A slab can heave on one side and settle on the other side at the same time. A provider must map both patterns before choosing a method.
Signs you need it
Diagonal cracks in walls, especially at door and window corners, are a common slab sign. Stair step cracks in brick veneer also point to slab movement. Floors that slope toward one corner, tile that cracks in a line and doors that stick in dry months all deserve a level check.
Plumbing signs matter too. A slab leak can show as a high water bill, a warm spot on a floor, a sound of running water or damp soil near the slab. A provider should ask about plumbing history before recommending piers. A leak that is not fixed can keep moving soil after piers are installed.
Process step by step
First, the provider measures floor elevations inside. It creates a map with high and low points. It notes crack locations on the same map. That map shows whether movement is local or across the whole slab.
Second, the provider checks outside. It looks at grading, gutters, downspouts, irrigation and trees. It looks for water pooling near the slab. It asks about plumbing leaks and past repair work.
Third, the provider proposes piers or other support. Exterior piers go around the slab perimeter. Interior piers go through the slab where an interior area has settled. The provider should explain why each pier location was chosen.
Fourth, the crew installs piers to a stable layer. It then lifts the slab in small steps, where lifting is planned. Lifting should be slow and monitored. A fast lift can crack walls, tile and plumbing.
Fifth, the crew seals cracks, fills voids where needed and checks floor levels again. It should test plumbing after interior pier work. It should give you a record of pier locations, depths and lift amounts.
Materials and options
Steel push piers are driven into the ground using the weight of the house as resistance. They can reach deep stable soil. Helical piers are screwed into the ground with a rotating shaft. They can be installed with less house weight and in tighter access areas. Concrete piers, including drilled piers, use concrete and steel to form a deep support column.
Each pier type has limits. Push piers need enough house load to drive them. Helical piers need soil that allows screw installation. Concrete piers need curing time and access for drilling. See Foundation leveling and piering for a fuller pier comparison.
Void filling uses grout or foam under a slab to fill gaps left by settled soil. It can support a slab that has a void but has not settled far. It does not replace piers where deep soil movement is active. A provider should explain when void filling is enough and when piers are needed.
Post tensioned slabs need special care. Those slabs have steel cables under tension inside the concrete. Cutting or drilling a post tensioned slab without locating cables can damage the slab and create a safety risk. Tell the provider if your slab is post tensioned, or if you do not know. The provider should locate cables before drilling.
Cost factors
Pier count is the main cost driver. A slab that needs piers on one side costs less than a slab that needs piers around the full perimeter and inside. Pier depth also matters. Deeper piers take more material and labor.
Interior piers cost more than exterior piers in most cases. Interior work requires floor protection, slab cutting, dust control and finish repair. Plumbing testing and repair after interior work can add cost.
Drainage work may be separate. Grading, gutter work and surface drains help soil moisture stay even. They do not replace piers, but they can reduce future movement. Ask for each item on its own line.
We do not publish a single price range here. Slab size, pier count, pier depth and interior work vary too much. An on site quote after floor level measurements is the useful price for your slab.
How to choose a provider
Ask for a floor level map before work, with pier locations, type and planned depth on that map.
Ask about post tensioned cable location if your slab may be post tensioned. Ask about plumbing testing after work. Ask about permits and inspections in your city. Ask for references for slab jobs of similar size and soil type.
Check licensing that applies to your job. Ask for proof and check it when you can. For a large pier job, compare two scopes. Look for differences in pier count, pier type, interior piers and finish work.
How our referral works
We do not choose a slab method or set a price. The provider should give a written scope and price before work starts.
Cities in this batch
See the home page for the full city list in this batch.
Frequently asked questions
What is a slab on grade foundation?
A slab on grade is a concrete slab poured at ground level. It serves as both floor and foundation. Walls sit on the slab edge or on a thickened edge beam. Plumbing and wiring often run under or through the slab. That layout makes under slab leaks and soil movement harder to see, so floor levels and crack patterns matter.
Why do slabs crack and settle unevenly?
Slabs settle unevenly when soil under one part moves more than soil under another part. Expansive clay, poor drainage, plumbing leaks and tree roots can all create that contrast. A slab that settles evenly may show few signs. A slab that settles unevenly shows cracks, slopes and sticking doors, because one part drops or lifts relative to the rest.
What is the difference between lifting and stabilizing a slab?
Stabilizing stops further movement by supporting the slab on deeper soil. Lifting raises a settled part back toward level. A job may do both, or only one. Ask the provider which goal applies to your slab. A stabilization job that does not lift will leave a slope in place, even if future movement stops.
Do slab repairs damage floors and plumbing?
Pier work can crack tile, shift plumbing and disturb finishes. A provider should warn you about those risks before work starts. Interior piers require holes through the slab and floor. Exterior piers avoid interior holes but may not reach a settled interior area. Ask how the provider will protect floors and test plumbing after work.
How do I know if a slab pier job worked?
Check floor levels before and after work, with the same measurement points. Check doors, cracks and trim gaps after work. Ask for a written record of pier locations, depths and lift amounts. A provider should also explain what monitoring to do in the months after work, and what to report if cracks reopen.
Common questions
What is a slab on grade foundation?
A slab on grade is a concrete slab poured at ground level. It serves as both floor and foundation. Walls sit on the slab edge or on a thickened edge beam. Plumbing and wiring often run under or through the slab. That layout makes under slab leaks and soil movement harder to see, so floor levels and crack patterns matter.
Why do slabs crack and settle unevenly?
Slabs settle unevenly when soil under one part moves more than soil under another part. Expansive clay, poor drainage, plumbing leaks and tree roots can all create that contrast. A slab that settles evenly may show few signs. A slab that settles unevenly shows cracks, slopes and sticking doors, because one part drops or lifts relative to the rest.
What is the difference between lifting and stabilizing a slab?
Stabilizing stops further movement by supporting the slab on deeper soil. Lifting raises a settled part back toward level. A job may do both, or only one. Ask the provider which goal applies to your slab. A stabilization job that does not lift will leave a slope in place, even if future movement stops.
Do slab repairs damage floors and plumbing?
Pier work can crack tile, shift plumbing and disturb finishes. A provider should warn you about those risks before work starts. Interior piers require holes through the slab and floor. Exterior piers avoid interior holes but may not reach a settled interior area. Ask how the provider will protect floors and test plumbing after work.
How do I know if a slab pier job worked?
Check floor levels before and after work, with the same measurement points. Check doors, cracks and trim gaps after work. Ask for a written record of pier locations, depths and lift amounts. A provider should also explain what monitoring to do in the months after work, and what to report if cracks reopen.