How Do You Repair a Slab Foundation?
Slab foundations fail in three distinct ways: surface cracking, differential settling, and plumbing leaks beneath the slab. Each has a different repair approach.
Slab Cracking: Seal to Prevent Water Infiltration
Most slab cracks are shrinkage cracks that formed in the first 1 to 5 years after construction. They are cosmetic rather than structural in most cases. Action: seal with a polyurethane or epoxy crack sealant to prevent water infiltration into the sub-base (which accelerates further settlement) and prevent insect infiltration. A crack in a load-bearing area of the slab (under a load-bearing wall) that has significant displacement (one side higher than the other): warrants a structural engineer assessment before sealing. A growing crack (getting longer or wider over time): indicates active settlement and requires assessment before repair. (For more on this, see Foundation Crack Repair: What Type of Crack Do You Have?.)
Slab Settling: Mudjacking or Foam Injection
A slab section that has settled (dropped relative to adjacent sections): typically caused by erosion or consolidation of the sub-base soil below. Mudjacking ($3 to $6 per sq ft) or polyurethane foam injection ($5 to $25 per sq ft) lifts the settled section back to grade. For interior slab settling (a sunken living room or kitchen floor): mudjacking is technically feasible but requires access through the finished floor surface — a significant disruption. Foam injection with smaller holes ($5 to $25 per sq ft, 5/8-inch holes): less disruptive and preferred for interior slab work. If the settling is due to a plumbing leak beneath the slab (which is the most common cause of interior slab settling): the plumbing leak must be repaired before the slab can be lifted, or the repaired slab will re-settle from the ongoing water erosion.
Plumbing Leaks Below the Slab
A plumbing leak beneath the slab (a common failure mode in homes with cast iron or copper slab plumbing): identified by a sudden spike in the water bill, wet or warm spots on the floor, the sound of running water with all fixtures off, and mold or efflorescence appearing at slab joints. Detection: professional leak detection using acoustic, thermal, or pressure testing methods ($200 to $600). Repair options: break-and-repair (saw-cutting through the slab, excavating to the pipe, repairing the pipe, and patching the slab: $2,000 to $5,000 per location), or slab bypassing (rerouting the plumbing above-grade through attic and walls, avoiding slab penetration: $4,500 to $13,000 for a whole-house repipe, depending on house size).
Working With a Contractor on This Project
Getting the right outcome on any home services project starts before the work begins. A few consistent practices make the difference between a smooth project and a frustrating one.
Get at least two or three quotes. A single quote gives you no basis for comparison. Two or three quotes reveal the market rate for the work, expose scope differences between bidders, and let you assess contractor communication quality before any commitment is made. The lowest bid is not automatically the best value if the scope is thin or the materials are underspecified.
Ask for licenses and insurance before work starts. Verify current general liability insurance and, for any work involving workers on your property, workers compensation coverage. Licensing requirements vary by state and trade; confirm the specific requirements in your jurisdiction. A licensed contractor who carries appropriate insurance protects both parties if something goes wrong during the project. (For more on this, see Questions to Ask Before Hiring a Foundation Repair Contractor.)
Get the scope in writing. A written proposal that specifies materials, labor scope, timeline, what is included (permits, cleanup, disposal), and warranty terms is the foundation of a professional engagement. Verbal agreements on any of these points invite misunderstanding. For any project over $500, written scope is non-negotiable.
Clarify the payment schedule upfront. A reasonable payment schedule ties major payments to project milestones: a deposit at signing, a payment at material delivery or project start, and a final payment at completion after a walkthrough confirms satisfaction. A contractor who requires full payment upfront before work begins is a red flag in any trade.
Making a Confident Decision
The information in this article is designed to help you ask better questions of the professionals you work with, evaluate their answers with more confidence, and understand the decisions involved in this type of home services project. It is not a substitute for professional assessment of your specific home. (For more on this, see Questions to Ask a Foundation Repair Contractor.)
Every home is different. Roof slopes, local weather, tree exposure, soil conditions, and existing system condition all affect what the right solution is for your specific situation. The general principles here apply broadly, but a professional who assesses your home in person will give you guidance that accounts for the details that general articles cannot.
When you are ready to move forward, getting at least two or three quotes from licensed, insured, local contractors is the most important practical step. It lets you compare approaches, assess contractor quality, and confirm that the solution proposed matches your specific situation and budget.
Cost figures on this page were checked against published pricing on September 2, 2026. How we source cost data.
