CIPP (Cured-in-Place Pipe) Lining

Why this matters

CIPP (cured-in-place pipe) lining is the trenchless method that lets a contractor rehabilitate a failed sewer line without trenching across the customer's front yard, driveway, or finished landscaping. Done right, CIPP delivers a 50-year service life with one day of work and minimal site disruption. Done wrong, it traps a failed line inside an inadequately cured liner that delaminates in 2 to 5 years, and the customer ends up paying for both the failed CIPP and the full trench replacement that should have been done in the first place. The technical work is repeatable; the project-selection decision (which lines are CIPP candidates and which are not) is where most failed CIPP projects start.

What CIPP actually is

A felt or fiberglass tube ("the liner") impregnated with a thermosetting resin (epoxy, polyester, or vinyl ester) is inverted or pulled into the host pipe. The liner is pressed against the host-pipe wall by air, water, or steam pressure. The resin cures (heat, UV, or ambient temperature), forming a structurally-independent new pipe inside the old one.

Once cured, the new "pipe in pipe" is structurally sound on its own and bonded to the host. Outside-pipe failures (further root intrusion, future cracks) do not affect the liner; the liner is the new flow path.

ASTM F1216 governs the standard for CIPP rehabilitation. ASTM F2019 covers pulled-in-place lining; ASTM F2599 covers UV-cured lining.

Where CIPP works

Best candidates:

• Continuous run with no major branches in the section to be lined (or branches that can be reinstated by robotic cutting)
• Pipe diameter in the residential and small-commercial range (4 inch through 12 inch typical; up to 60 inch for municipal)
• Host pipe with structural integrity remaining (the liner conforms to the host shape; a fully collapsed host cannot be lined)
• Length under 200 ft for residential, longer for municipal
• Material is cast iron, clay, concrete, or even PVC (any rigid material with structural shape)
• Access to one end (one-sided pull or invert; two-sided improves quality but is not required)

Poor candidates:

• Completely collapsed host (the liner has nothing to conform against)
• Severely deformed host (ovaling over 30 percent; liner takes the wrong shape)
• Heavy infiltration (groundwater entering during cure produces a poor bond and weak liner)
• Multiple severe offsets at joints (the liner cannot bridge step changes in shape)
• Active wet conditions that prevent dewatering before cure
• Galvanized steel host with heavy scale (liner does not adhere well to scale)

Curing methods

Three curing methods cover most residential and commercial CIPP work:

Steam cure

Steam at 180 to 220 F pressurizes the liner and activates the resin. Cure time 2 to 6 hours depending on diameter and resin chemistry.

• Pros: fast cure, widely available, well-understood
• Cons: requires steam boiler and water source; more equipment on site

Hot water cure

Heated water at 140 to 180 F pressurizes the liner. Cure time 4 to 8 hours.

• Pros: gentler than steam, lower energy
• Cons: slower; requires large water source

UV cure (light cure)

Resin formulated to cure under UV light. After the liner is inverted, a UV light train is pulled through the liner, curing in 30 to 90 minutes per typical length.

• Pros: fastest cure, smallest crew, no thermal equipment
• Cons: requires fiberglass liners (felt does not transmit UV); higher equipment cost; quality-control via in-process temperature monitoring

UV cure has been gaining residential share since 2018; most modern shops are buying UV equipment for new install or replacing aging steam rigs.

Ambient cure

Some resin systems cure at ambient temperature over 24 to 72 hours. Used for emergency situations where heat or UV equipment is unavailable, or for specific resin formulations.

Resin systems

Residential sewer lines almost always use polyester or vinyl ester. Potable-water service lines (yes, you can line potable lines too) require epoxy and NSF/ANSI 61 certified product (3M Scotchkote 169LV, Nu Flow, Pipe Restoration).

Step-by-step CIPP procedure

Step 1: Pre-line inspection

Run a sewer camera (see sewer camera image interpretation reference) to document:

• Material, diameter, condition
• Length to be lined
• Branch locations (these must be reinstated after lining)
• Existing cleanout and access points
• Any deformations or structural issues that affect cure

Document with video; this is the baseline for the warranty.

Step 2: Cleaning

A CIPP cannot bond to grease, scale, debris, or soft material. Pre-cleaning is mandatory:

• Mechanical descaling (chain knocker, descaling tool) for cast iron with heavy scale
• Hydrojetting at 4,000 to 8,000 psi for grease and soft debris
• Root cutting for any remaining roots
• Final inspection camera pass to verify cleanliness

A line that is not properly cleaned produces a CIPP that delaminates within 1 to 3 years. This step is the single highest-leverage quality control in the entire procedure.

Step 3: Bypass and dewater

The line cannot have flowing water during inversion and cure. Bypass:

• Block the line upstream
• Pump flow around the lining section
• Drain residual water from low spots
• For residential, schedule with the homeowner to minimize flow (no laundry, dishwasher, showers during the lining window)

Step 4: Liner preparation (wet-out)

The dry felt or fiberglass liner is impregnated with resin in a controlled "wet-out" process:

• Resin mixed at exact specification (resin plus catalyst, weighed and timed)
• Liner pulled through a wet-out machine that distributes resin throughout the fabric
• Saturated liner sealed in a refrigerated transport cooler if not immediately deployed (resin pot life is short at ambient)

Wet-out is typically done on the truck or at the shop. Off-site wet-out requires keeping the saturated liner cold (under 50 F) until install.

Step 5: Inversion or pull-in

Two installation methods:

Inversion (ASTM F1216). The saturated liner is turned inside out into the host pipe by water or air pressure, so the resin face rolls onto the pipe wall as the liner advances.

• Liner is loaded into an inversion drum or a standpipe at the access point, resin side in.
• Water head or air pressure inverts the tube down the line; the leading edge continuously turns outward against the host pipe.
• Pressure is held to hold the liner tight to the wall through cure.
• Best for: full-length runs from a cleanout or manhole, lines with bends where the rolling action helps the liner track, and jobs where a tight fit against an irregular wall matters.
• Watch for: enough head or pressure to reach the far end, calibrated to the liner and the manufacturer's spec, and no stalling mid-run. A liner that stops advancing and starts curing is a very bad day.

Pull-in-place (ASTM F2019). The saturated liner is pulled through the host pipe with a winch line, then inflated against the wall with a calibration bladder or tube.

• A rope or cable is run through the line from the far access point.
• The wet-out liner is pulled in flat, resin side out, to the target position.
• A bladder inside the liner is inflated with air or water to press it against the host pipe and hold it through cure.
• Best for: sectional and spot repairs, runs where you have access at both ends, and situations where you need precise positioning over a specific defect.
• Watch for: dragging the liner over sharp scale or a broken edge on the way in, which damages the tube before it is ever set, and bladder pressure held per spec for the full cure.

Cure is initiated the same way for either method once the liner is in position and under pressure: ambient, hot water, steam, or UV light, per the resin system. Follow the manufacturer's time and temperature schedule exactly and log it. Pulling pressure before full cure is the second most common cause of failure after inadequate cleaning.

Step 6: Run and verify the cure

The curing methods section above covers what each method is and when to pick it. This step is about running the one you picked and proving it happened.

Hold pressure on the liner for the entire cure. The pressure is what keeps the tube against the host wall while the resin goes off; the heat or light is only half the job. Do not adjust pressure to chase a reading unless the manufacturer's procedure tells you to.

What the tech does at this step:

• Set and hold the pressure the manufacturer specifies for the liner diameter and length. Watch the gauge continuously, not on a timer. A slow drop means a leak, a boot slip, or a tear, and it needs to be found now rather than after cure.
• Monitor temperature where the spec says to monitor it, typically at the far end and at the liner-to-host interface, using the thermocouples or in-liner sensors the system uses. On UV, monitor the light train speed and the in-process readings the equipment reports.
• Run the full hold time on the manufacturer's schedule. The clock starts where the schedule says it starts (often when the monitored point reaches the target temperature, not when you opened the steam valve). Getting that wrong shortens the cure by the whole heat-up period.
• Log it as you go: start time, pressure held, temperature readings at each interval, heat or light source settings, hold time, and who watched it. This log is part of the warranty package. A cure you cannot document is a cure you cannot defend.
• If a spec requires a cure sample, usually municipal or commercial work, prepare it alongside the liner per that spec so it sees the same cure the pipe saw. Sample requirements and test values come from the spec, not from you.

Watch for: a temperature reading that will not come up at the far end. That is the section that has not cured, and running the clock out anyway does not fix it. Stop, find the cause (heat loss to groundwater, a low spot holding water, an undersized source), and follow the manufacturer's guidance before continuing.

Step 7: Controlled cool-down and pressure release

Cure is not finished when the timer ends. The liner has to come down in temperature on the manufacturer's cool-down schedule, still under pressure, before anything gets released.

• Bring the temperature down at the rate the manufacturer specifies. On steam and hot water this usually means introducing cool water gradually or stepping the heat source down; the exact method and rate belong to the resin system and the equipment, so follow that schedule.
• Keep pressure on the liner throughout cool-down.
• Release pressure only after the liner has reached the release condition in the manufacturer's schedule, and release it in a controlled way rather than dumping it.
• Log the cool-down the same way you logged the cure.

Why this matters, because it is where good installs get ruined at the last minute:

• Releasing pressure early lets a resin that is still soft pull away from the host wall. You get an annular gap, wrinkling, or a liner that has relaxed out of round. Nothing about the finished camera pass will look obviously wrong on day one, and the failure shows up later as delamination or infiltration behind the liner.
• Cooling too fast shocks the cured resin. The liner and the host pipe do not move the same amount as temperature drops, and a fast drop puts that difference into the resin and the bond line as stress. That is how you get crazing, cracks at the ends, and a bond that lets go.

Both failure modes cost you the same thing: a liner that passed the post-cure camera pass and failed inside the warranty period. There is no repair for a cure that was rushed. The pipe gets lined again or dug up.

Step 8: Reinstate branch connections and laterals

Every branch you documented in Step 1 is now covered by the liner. Reinstatement is opening each one back up. Miss one and the customer has a fixture, a floor drain, or a whole branch line with nowhere to drain.

The work is done with a robotic cutter: a small tracked or skidded unit with its own camera and a high-speed cutting head, fed down the lined pipe on an umbilical and driven from a control station on the surface.

Locating each branch:

• Start from the footage marks on the Step 1 baseline video. That video is why you recorded footage on the way in.
• Confirm on the cutter camera. A covered branch usually shows as a dimple or a shadowed depression where the liner has pressed slightly into the branch opening. On a tight-fitting liner the dimple can be faint, which is exactly why you do not rely on the dimple alone.
• If a branch will not come up on camera and the footage is uncertain, locate it from the fixture side (run water, or send a sonde down the branch) before you cut. Cutting to find a branch is how you cut in the wrong place.

Cutting:

• Center the cutter on the opening and open it out to the full branch diameter, working out from the middle rather than starting at an edge.
• Keep the cut inside the branch profile. The target is a clean, full-diameter opening flush with the liner wall.
• Inspect each reinstatement on camera before moving to the next one, while the cutter is still there.
• Log every reinstatement with its footage so the count on the finished report matches the branch count from Step 1.

What a bad reinstatement causes:

• Undercut, meaning the opening is smaller than the branch. The remaining liner is a shelf across the bottom of the branch that catches paper, grease, and wipes. The customer gets recurring stoppages at a spot that was fine before you lined it.
• A flap or a tag of liner left hanging at the edge. Same result, faster, and it can also fold over and choke the branch.
• Overcut past the liner into the host pipe or the annular space. You have opened a path behind the liner for roots and groundwater, which is most of what you lined the pipe to stop.
• Off-center or partial cut. Flow restriction plus a turbulent entry that collects debris.

Watch for: heat and dust from the cutting head, and a cutter that stalls or bogs. Follow the cutter manufacturer's procedure for feed rate and bit selection for the liner material. Forcing it damages both the head and the liner edge you are trying to leave clean.

Step 9: Final CCTV inspection and acceptance

Restore flow last, and only after the finished line has been inspected.

Run a full-length camera pass over the entire lined section, same direction and same footage reference as the Step 1 baseline so the two videos read against each other.

What you are looking at:

• Full-length liner with no wrinkles, fins, folds, or lifted sections
• No dry spots, soft areas, blistering, or delamination
• End seals at both terminations, with no annular gap where the liner meets the host pipe or the access point
• Every branch from Step 1 reinstated, clean, full diameter, no shelf and no tag
• No standing water where the line should drain, which would flag a low spot or a sag that the liner did not correct (CIPP conforms to the host; it does not fix grade)
• Debris and cuttings flushed out

Then remove the bypass, pull the plugs, and restore normal flow. Run water from the fixtures and confirm each reinstated branch drains.

The acceptance package is what turns the job into a warranty you can stand behind. It should carry:

• The Step 1 pre-line video, which is the baseline. It is what proves the condition you started with, and it is the only thing that separates a defect you lined over from a defect you caused.
• The post-line video, referenced to the same footage marks
• The cure and cool-down logs from Steps 6 and 7, with pressure and temperature readings
• Liner size, length, resin system, and the resin batch or lot information from wet-out
• The reinstatement list with footages, matched against the branch list from Step 1
• Any cure sample results the spec required

Give the customer a copy. File a copy. When somebody calls in year four, the baseline video and the cure log are the two documents that settle whether the liner failed or the rest of the system did.

References

• ASTM F1216 (Standard Practice for Rehabilitation of Existing Pipelines and Conduits by the Inversion and Curing of a Resin-Impregnated Tube).
• ASTM F2019 (Pulled-in-Place CIPP).
• ASTM F2599 (UV-cured CIPP).
• NASSCO LACP (Lateral Assessment Certification Program).
• NSF/ANSI 61 (for potable-water-side lining).
• EPA Effluent Limitation Guidelines.
• Manufacturer literature: Insituform, Perma-Liner, LightStream UV, MaxLiner, AquaBlast LiteRoad UV.
• Manuall internal: Plumbing Sewer Camera Image Interpretation, Plumbing Trenchless Sewer Repair, Plumbing Clear Main Sewer Line.