What is sewer rehabilitation?
Sewer rehabilitation is restoring the function of an existing drain or sewer without replacing the pipe. Instead of digging up the street or the garden, the old pipe is given a new, watertight wall on the inside. This is called trenchless rehabilitation, and it is now the standard approach to leaking or cracked drains.
Why rehabilitate rather than replace
A sewer typically lasts sixty to eighty years, but fails earlier through settlement of the ground, root ingress, attack on the concrete by sulphuric acid formed from rotting sewage, or simply badly laid joints. Replacement means excavation, traffic disruption, dewatering and reinstating the surface. Rehabilitation can often be done in a day from the existing manholes, and therefore usually costs considerably less.
Relining with a cured-in-place liner
The most common technique is CIPP — cured-in-place pipe, also called relining or pipe-in-pipe:
- Clean and survey — the line is cut out and jetted clean, then a camera records cracks, sags and incoming connections.
- Insert the liner — a flexible felt or glass-fibre liner impregnated with resin (polyester, vinyl ester or epoxy) is winched in or inverted with air or water pressure.
- Cure — the resin cures using hot water, steam or UV light, forming a seamless new pipe inside the old one.
- Reinstate connections — a cutting robot reopens the lateral connections.
- Final survey — a second camera run, usually issued as a report.
The new inner pipe is strong enough to carry the load on its own and is expected to last fifty years or more. Because the wall is smooth, the small loss of diameter matters little: flow capacity usually stays the same or improves.
Other techniques
- Patch repair (short liner) — a short liner a few millimetres thick over just the damaged section; ideal for a single crack or a leaking joint.
- Top hat — specifically restores where a house connection meets the main.
- Injection grouting — resin forced into a leaking joint to stop groundwater entering.
- Pipe bursting — where the pipe is too small or has collapsed, the old pipe is split apart and the new one pulled straight in behind it.
Watch out for work inside the house
Curing releases fumes; polyester liners release styrene among others. Ventilate, and keep occupants away for as long as the supplier specifies. Always ask for the camera survey both before and after the work — it is your only proof that anything was actually repaired.
Related terms
- Sewer
- Stoneware pipe
- Settlement joint
- Drainage settlement compensator
- Rainwater drainage
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.