Drain Relining Explained: When No-Dig Repair Works
In short
Drain relining repairs a damaged pipe from the inside. A resin-impregnated liner is drawn or inverted into the existing drain, pressed against the pipe wall and cured to form a new pipe within a pipe. It suits cracks, fractures, open or displaced joints, root entry points and general deterioration where the pipe still holds its shape. It is not suitable where the drain has collapsed, lost its fall, or is too badly deformed to accept a liner — those cases need excavation. A CCTV survey decides which applies.
Relining — also called no-dig or trenchless repair, and CIPP (cured-in-place pipe) — repairs a drain from the inside rather than digging it up. The existing pipe becomes the mould for a new one.
It is often the cheaper and far less disruptive option, particularly under driveways, patios, extensions and roads. It is not a universal answer, and the honest version of this subject is mostly about knowing where the line falls.
What relining actually involves
A felt or fibreglass liner is saturated with a two-part resin, then either winched into position and inflated against the pipe wall, or inverted into the drain under air or water pressure. Held in place while the resin cures, it hardens into a smooth, jointless sleeve bonded to the original pipe.
Two forms are used depending on the defect: a patch (or localised) liner covering a short length such as a single cracked joint, and a full-length liner running between chambers where the whole run has deteriorated. Branch connections are re-opened afterwards with a cutter, and junctions can be sealed with a purpose-made hat or top-hat liner.
Which defects relining suits
Relining is a good match where the pipe is damaged but structurally still there.
- Longitudinal and circumferential cracks
- Open, displaced or leaking joints
- Root entry points, once the roots have been cut out
- Corroded or worn pipe walls and lost mortar in older clay drains
- Minor infiltration of groundwater through defects
- Runs beneath driveways, buildings, patios or highways where excavation is costly
When relining is not appropriate
Some defects cannot be solved from the inside, and a contractor who says otherwise is guessing.
- A fully collapsed section, where there is no host pipe left to line against
- Severe deformation or ovality that will not accept a liner
- A run laid to the wrong fall or with standing water — a liner does not change the gradient
- Badly displaced joints where the pipe ends no longer line up
- Missing sections, or a drain that needs re-routing rather than repairing
- Very small-bore or heavily stepped runs where the liner cannot be installed cleanly
Preparation matters more than the liner
Most lining failures come from poor preparation. The pipe has to be cleared and cleaned properly first — jetting out silt, cutting back roots, removing scale and any intruding connection — and then surveyed again so the liner bonds to a clean surface with nothing trapped beneath it.
After curing, the run is re-surveyed to confirm the liner is fully formed, correctly positioned and that all branch connections are reinstated.
Relining compared with excavation
The right choice depends on the defect and what is above the pipe, not on a general preference for one method.
| Relining | Excavation | |
|---|---|---|
| Suits | Cracks, open joints, root entry, worn pipe | Collapse, lost fall, missing or re-routed pipework |
| Surface disruption | Minimal — works through existing access | Digging and reinstatement of the ground above |
| Typical time on site | Often a day or less for a domestic run | Longer, depending on depth and reinstatement |
| Effect on bore | Slight reduction, offset by a smoother surface | New pipe at full bore |
| Decided by | CCTV survey of the affected run | CCTV survey of the affected run |
Why the survey comes first
Every decision above rests on seeing the pipe. A CCTV survey shows the defect type, its position and depth, the condition of the surrounding pipe and whether the run holds water — which is what determines whether a liner will work.
It also protects you commercially: with a recorded survey you can compare quotes for the same defined defect rather than competing descriptions of what might be wrong. Where a defect genuinely cannot be lined, excavation is the honest answer — our Devon job replacing a cracked run that had lost its fall is an example of a drain that needed replacing rather than lining.
Still not resolved? CCTV Drain Surveys can help
Find out exactly what's going on inside your drains, without guessing. Our engineers are available 24 hours a day with no call-out charge, and you get a fixed price before any work starts.