How Are Sewer Lines Repaired Under a Concrete Slab?
Published
Verify before you rely on this guide. This is general educational information, current as of October 11, 2026. Codes, permit rules, fees, prices, product warranties and industry practices change, and every property is different. You must confirm up-to-date information with the City of Pasadena or your local building authority, a licensed plumbing or sewer contractor, and the sources listed in this guide before making any decision.
An under-slab sewer problem does not always mean the entire floor has to be broken up. The best repair may involve a small, targeted opening, cured-in-place lining through an accessible cleanout, or a properly designed reroute. The deciding factors are where the failure actually is, what condition the existing pipe is in, and whether the proposed route will drain by gravity.
Before agreeing to cut concrete, ask the plumber to document the damaged reach and explain what additional testing—if any—confirms the problem.
Does a slow drain mean there is a sewer leak under the slab?
Not necessarily. Slow drains, gurgling toilets, and recurring backups can result from a blockage, roots, displaced joints, or deterioration anywhere along a shared drain. Odors may have several causes, including dry traps and accessible fittings.
A sewer blockage and an under-slab sewer leak are different diagnoses. A camera may reveal a visible crack or separated joint but cannot always prove that wastewater is escaping into the soil outside the pipe. Testing may be needed when the cause remains uncertain.
Be wary of descriptions borrowed from water-supply leaks. A running water meter, continuously flowing pressurized water, or a warm floor may point toward a supply or hot-water system issue; they are not reliable signs that a gravity sewer has broken.
How does a plumber find the damaged section?
A technician may inspect the accessible line with a sewer camera, recording cracks, offsets, roots, debris, and standing water. A compatible sonde and aboveground locator can help mark an approximate underground position and depth. The equipment's readings are aids to planning—not proof of an exact underground profile or every hidden defect.
Ask for a sketch showing where the camera entered, what stretch it inspected, where the suspected failure sits, and whether the camera could pass it. When video findings are inconclusive, a professional may recommend a controlled test appropriate to the pipe and suspected failure. The right test depends on the actual plumbing layout and condition.
Basic CCTV also does not measure sewer slope. If the recommendation is based on a suspected belly, ask what separate elevation or grade evidence supports that diagnosis. See our sewer-belly explanation for more.
Option 1: Targeted slab opening and spot repair
If a short section has a confirmed break, an accessible repair may involve cutting and removing concrete over that section, excavating safely, replacing the failed pipe, and reconnecting it to sound pipe at the intended grade.
The contractor needs to assess nearby structural components and utilities before cutting. Depending on the building and slab, the work area may contain reinforcement, post-tension elements, or other buried systems; no one should assume the slab is plain concrete.
Ask exactly what is included in the price: dust protection, concrete removal, pipe replacement, testing, backfill, slab patching, and any flooring restoration. A small pipe repair can still require careful interior preparation and finishing.
Option 2: Lining an eligible pipe from an access point
Cured-in-place pipe lining (CIPP) creates a new interior wall inside an existing pipe. It may reduce the need to open a slab when the pipe can be cleaned, measured, and accessed through a suitable cleanout or another planned opening. NASSCO's lateral lining guideline describes methods that can use cleanouts or other access points; it does not promise zero excavation.
Lining must fit the actual pipe geometry. A seriously collapsed line, an obstruction, a severe offset, or an uncorrected grade defect may make it inappropriate. A liner generally follows the host pipe's existing route; it does not raise a belly or make wastewater flow uphill.
Ask who will verify that branch connections remain open and what final inspection or installation records the contractor will provide. Our lining process guide explains the stages.
Option 3: Rerouting around the slab
Sometimes replacing the original route would be disruptive or technically difficult. A contractor may evaluate a new route through an accessible area or around part of the building instead.
A reroute is not simply “putting the pipe somewhere else.” It must maintain sufficient gravity drainage, suitable connections, access for cleaning, required materials, and safe separation from other work. Where the project affects structural elements or other building systems, the required design and approvals may be more involved.
Ask for a route diagram with new connections and the portions of old piping that will be taken out of service. The contractor should explain what walls, floors, and outdoor areas are affected and who restores them.
What about pipe bursting under a slab?
Pipe bursting replaces an old pipe while displacing the old material outward. It can work on some routes, but it is not a default under-slab solution. Access, soil displacement, utilities, foundations, the old pipe's alignment, and the location of connections can create serious limitations. NASSCO's rehabilitation matrix emphasizes site suitability; it does not treat pipe bursting as a way to automatically correct grade.
If bursting is proposed near a slab, ask where the equipment and new pipe will enter and exit, what other buried utilities are nearby, and how the installer will manage displacement risks. Compare that plan with a targeted excavation or reroute before committing.
What does the work involve for your household?
Regardless of method, expect a period when connected drains cannot be used normally. The potable water supply may stay on, but running a sink, shower, or washing machine still sends wastewater into the sewer. Follow the crew's instructions about fixture use and bypass arrangements.
Ask for a schedule that separately identifies diagnostics, access work, pipe repair, testing, and restoration. If sewage has backed up into living areas, keep people and pets away from contamination until the area is safe.
California excavation rules address locating buried installations and protective measures for exposed utilities and excavations; see the state excavation-safety regulation. Work should be planned by appropriately qualified personnel, not treated as a weekend cut-and-patch project.
How do you compare repair quotes?
Ask each bidder to use the same documented defect location and state the repair limits, new materials, access method, connections, testing, permits, and restoration. One quote that replaces a short pipe segment and another that reroutes several branches are not directly comparable.
For budget questions, use our under-slab sewer repair cost guide, which explains estimate components without inventing a Pasadena-wide average.
The takeaway
First locate and characterize the failure. Then choose the least disruptive method that actually corrects it. Lining, spot excavation, and rerouting are different tools; none is the right answer for every under-slab pipe.