What is trenchless pipe lining?
Trenchless pipe lining rebuilds a damaged pipe from the inside, so it doesn't have to be dug up. Through a cleanout, a manhole or a small access pit, a flexible liner soaked in resin is pulled or inverted into the old pipe, pressed against its walls, and cured into a hard new pipe. The result is a jointless, corrosion-resistant pipe inside the old one, often installed in a day, while the parking lot, landscaping or finished floor above stays in place.
Lining is one of several trenchless methods. Others include sectional point repairs for single defects, pipe bursting to pull a new pipe through the old one, and epoxy coatings sprayed or blown onto the inside of smaller pipes. They're most often used on sewer laterals, storm lines and interior drain lines. Some coatings are also used on pressurized water lines.
Trenchless isn't always possible. It depends on the condition and shape of the existing pipe, so the work always starts with cleaning and a camera inspection. A broken, offset or root-filled pipe is a good candidate. A collapsed pipe or one with a deep sag usually is not.
Which trenchless method fits which problem?
| Method | How it works | Good for | Limits |
|---|---|---|---|
| CIPP lining | A resin-saturated liner is inverted or pulled in, then cured with hot water, steam or UV light. | Long runs with cracks, joint gaps and root entry. | Can't correct sags. Needs the pipe to keep its shape. |
| Sectional repair | A short liner is placed and cured at one defect. | Isolated cracks or a single bad joint. | Not cost-effective for many defects along a run. |
| Pipe bursting | A bursting head breaks the old pipe outward while new pipe is pulled in behind it. | Replacing or upsizing failed pipe without trenching. | Needs launch and receiving pits, and room to displace soil. |
| Epoxy coating | Epoxy is sprayed or blown onto the cleaned pipe interior. | Smaller drains, stacks and branches with lots of fittings. | Pipe must be structurally sound enough to coat. |
How is a pipe lined?
Clean and inspect
The pipe is cleaned with jetting or cutters to remove roots, grease and scale. On cast iron that can mean descaling down to bare metal. A camera then records the cleaned pipe and measures its length, diameter changes and branch connections.
Measure and wet out
The liner is cut to length and saturated with resin, a step called wet-out, in a controlled way so the resin is evenly distributed.
Install and cure
The liner goes in through the access point, either inverted with air or water pressure or pulled in and inflated with a bladder, then cured. Hot water and steam cures take hours. UV-cured liners cure as a light train is pulled through them. Industry standards such as ASTM F1216 describe the inversion-and-cure process.
Reopen branches and verify
Where other lines join the lined pipe, a robotic cutter reopens each connection from inside. A final camera run checks for wrinkles, gaps and properly reopened branches, and the line goes back into service.
Lining vertical drain stacks
In multi-story buildings, cast iron stacks and their branches can be lined or coated from the roof vents and cleanouts. That avoids opening walls in every unit or suite. It takes careful sequencing, because each floor's fixtures have to be out of service while that section cures, but it's often far less disruptive than replacing stacks through finished spaces.
Questions to ask before you sign
Lining proposals can look alike on paper. Ask what liner material and resin will be used, how the liner's thickness was chosen for your pipe's diameter and depth, and how it will be cured. Ask how many branch connections will be reopened and how that will be verified. Ask what happens if the camera finds a defect during prep that rules out lining, and what the warranty covers. Clear answers to those questions are a good sign you're dealing with an experienced installer.
What are the signs a pipe may need lining?
- Recurring backups that come back weeks after the line is cleaned.
- Camera footage showing cracks, open joints or root intrusion along the run.
- A sewer route under paving, a building or landscaping you don't want to tear up.
- Cast iron with heavy scale or rot-through on the bottom of the pipe.
- Wet spots or sinking ground above a leaking drain.
- Sewer odors traced by smoke testing to a broken underground section.
- Repeated drain stack leaks inside walls of a multi-story building.
- A pre-purchase or sewer district inspection that flagged defects.
Why do pipes reach the point of needing a liner?
- Joint failure. Older clay and concrete pipe have a joint every few feet, and each one is a potential gap for roots and soil.
- Corrosion. Cast iron corrodes from inside, and sewer gases attack concrete above the waterline.
- Roots. Roots widen joints as they grow, turning small gaps into cracks.
- Ground movement. Settling and seismic shifts crack rigid pipe and offset joints.
- Age. Many commercial buildings still use original drain lines that have simply reached the end of their service life.
What should you gather before calling?
- Any existing camera video or reports, with footage counts to each defect.
- Site or building drawings showing the line route, size and access points.
- A list of which fixtures and areas drain through the affected line.
- Your operating hours, so lining can be scheduled when the line can be out of service.
- Any sewer district notices or requirements tied to the repair.
Pro tip: ask for before-and-after video
A reputable lining job comes with video of the cleaned pipe before lining and the finished liner after, including reopened branch connections.
Warning: lining won't fix a belly
If the pipe sags, the liner follows the sag and the line keeps clogging. Make sure the camera report checks grade before you approve lining.
What happens on a lining project?
- AssessmentCleaning and camera inspection to confirm the pipe is a lining candidate.
- ProposalMethod, liner type, cure method, length, access points and downtime, in writing.
- PrepFinal cleaning, bypass pumping if flow can't be stopped, and access set up.
- Install and cureLiner placed and cured, typically in a single working day for a lateral.
- ReinstatementBranch connections reopened from inside with a robotic cutter.
- Final videoPost-lining inspection and handover of records.
What affects the cost of trenchless lining?
| Factor | Effect on the job |
|---|---|
| Diameter & length | Larger, longer liners use more material and resin. |
| Pipe condition | Heavy descaling or root removal adds prep time. |
| Branches | Each reopened connection adds robotic cutting time. |
| Access | Missing cleanouts may need an access pit. |
| Flow control | Bypass pumping for lines that can't be shut down. |
What if the line is backing up now?
Lining is planned work, but a backup can't wait for it. The first step is clearing the line by jetting or cabling to restore flow, then cleaning up any contamination. Once the building is working again, the camera inspection decides whether lining is the long-term fix. For active sewage backups, call for emergency commercial leak repair.
Ventilation during curing
Some resin systems give off odors during cure. Crews should ventilate and keep traps filled so fumes don't enter occupied space.
Trenchless lining FAQ
How long does a pipe liner last?
Properly installed liners are designed for long service lives, often comparable to new pipe. Ask the installer for the expected design life and warranty terms for the specific product.
Does lining make the pipe smaller?
Slightly, by the liner's thickness. The smooth, jointless interior usually flows as well as or better than the rough old pipe.
Can lining be done on pressurized water lines?
Some epoxy coatings and liners are rated for pressure and drinking water. Lining is most common on drain and sewer lines, though.
Is lining cheaper than digging?
Often, once you count the paving, landscaping, floors and downtime that excavation would disturb. For a short, shallow line in open soil, digging can be cheaper.
Will my business have to close?
The affected line is out of service during install and cure, often for part of a day. Many jobs are scheduled overnight or on weekends.
What if my pipe is collapsed?
A collapsed section usually has to be excavated and replaced first. The rest of the line can sometimes still be lined.
Related services and areas
Older laterals under parking lots along the West Bothell corridor, and long private sewer runs in HOA communities around Brickyard Road–Queensgate, are frequent lining candidates. Diagnosis comes first under sewer and drain line leak repair. For every other leak type, see our Bothell leak repair overview.