What is a Lining

Lining is a trenchless method used to repair and rehabilitate damaged, aged, or deteriorating underground pipes by installing a resin-impregnated liner inside the existing pipe structure. This technique effectively creates a new pipe within the old one, restoring structural integrity, flow efficiency, and watertightness without the need for excavation. Lining is widely used in sewerage, drainage, and stormwater systems and is considered one of the most effective long-term repair strategies for a broad range of pipe defects.

By bonding tightly to the interior wall of the host pipe and curing into a hardened form, the liner forms a seamless, corrosion-resistant barrier that performs similarly to a new pipe, often with a service life of 50 years or more.

Purpose and benefits of lining

The main purpose of pipe lining is to restore functionality and structural stability to a damaged pipeline without digging up the ground. It is used in situations where pipes are cracked, leaking, corroded, misaligned, or infiltrated by tree roots. In some cases, lining is also used proactively to upgrade ageing infrastructure before major defects occur.

Key benefits of lining include:

  • No need for surface excavation, avoiding disruption to roads, gardens, or buildings

  • Suitable for a wide range of pipe diameters and materials

  • Long service life and structural reinforcement

  • Resistance to chemicals, corrosion, and abrasion

  • Reduced installation time compared to full pipe replacement

  • Maintains or restores hydraulic capacity

Lining is considered an environmentally friendly option because it reduces waste, preserves existing infrastructure, and requires fewer resources than traditional excavation.

How the lining process works

The lining process typically involves the installation of a flexible tube, saturated with a resin, into the damaged pipe using inversion or winching methods. Once in place, the resin is cured (hardened) to form a rigid, structural pipe that fits tightly within the host pipe. The process involves several stages:

  1. Inspection and assessment
    A CCTV survey is used to inspect the pipe and identify defects such as cracks, joint displacements, root ingress, or infiltration. This helps determine whether lining is appropriate and what length of pipe needs to be rehabilitated.

  2. Pipe cleaning and preparation
    The pipe is thoroughly cleaned using high-pressure water jetting or mechanical tools to remove debris, silt, scale, and obstructions. Any protruding connections or roots are trimmed to ensure a smooth internal surface for lining.

  3. Liner preparation
    A flexible liner made from felt or fibreglass is impregnated with a two-part resin, typically epoxy, polyester, or silicate. The resin saturates the liner fully to ensure strong adhesion and structural properties after curing.

  4. Insertion into the host pipe
    The liner is inserted using either inversion (pushed in using water or air pressure) or winching (pulled through with a rope or cable). Inversion is more common for longer or smaller diameter pipes.

  5. Curing
    Once in place, the liner is cured to harden the resin. This may be done using ambient temperature, hot water, steam, or ultraviolet (UV) light depending on the system used. The curing process can take from one hour to several hours.

  6. Final trimming and inspection
    After curing, the liner is trimmed at both ends to restore access points and re-open lateral connections using robotic cutting tools. A post-installation CCTV survey confirms the quality of the lining and ensures the pipe is fully rehabilitated.

Types of lining techniques

There are several variations of pipe lining, depending on the application and conditions on site. Common types include:

  1. Cured-in-Place Pipe (CIPP)
    The most widely used lining method. It uses a resin-saturated liner cured inside the pipe to form a new internal structure. Suitable for pipes from 100 mm to over 1500 mm in diameter.

  2. UV lining
    Uses light-sensitive resins cured with ultraviolet lamps pulled through the pipe. Faster curing time and high-quality control make it ideal for time-critical projects.

  3. Pull-in-place lining
    The liner is pulled into position rather than inverted and cured using steam, hot water, or ambient air. Useful in short runs or where inversion is not possible.

  4. Spray-on lining
    A resin or cementitious coating is sprayed onto the inside of the pipe rather than installing a liner. Less structural than full CIPP but useful for corrosion protection or sealing minor defects.

Typical applications

Lining is used across a wide range of environments and pipe systems. Typical applications include:

  • Foul water sewers with root intrusion, cracks, or leaks

  • Stormwater drains with structural defects or water infiltration

  • Industrial pipework subject to chemical exposure

  • Private lateral drains in domestic properties

  • Heritage sites or urban areas where excavation is restricted

  • Culverts and under-road crossings that are difficult to access

Lining is suitable for most pipe materials, including vitrified clay, cast iron, concrete, asbestos cement, and plastic (uPVC or HDPE).

Technical considerations

Successful lining depends on several technical factors, including:

  • Pipe condition: Lining cannot be installed in pipes that are completely collapsed or severely deformed. Some minimum structural integrity is required.

  • Diameter and length: Lining can be applied in pipes from around 75 mm up to several metres in diameter. Longer runs may require intermediate access points.

  • Flow control: The pipe must be isolated during installation. Temporary overpumping or bypass systems may be required.

  • Resin selection: The type of resin must match the application conditions, such as temperature, load, and chemical exposure.

  • Pipe bends and diameter changes: Liners can accommodate some changes in geometry but excessive distortion may prevent proper seating or curing.

Longevity and performance

When installed correctly, pipe lining systems are expected to last 50 years or more. They provide a smooth, jointless surface that reduces flow resistance and minimises the risk of future blockages. The cured liner typically has high tensile strength, resistance to pressure, and impermeability to both water and gases.

Independent testing and certification, such as WRc or BBA approval in the UK, help ensure that lining products meet required performance and durability standards.

Regulations and standards

In the UK, pipe lining installations must comply with various industry regulations and codes, including:

  • Building Regulations Part H

  • Water Industry Specification WIS 4-34-04

  • WRc’s Sewer Renovation Manual

  • BS EN ISO 11296 (for plastic pipe rehabilitation)

Local authorities or sewerage undertakers may also require pre-approval or inspections, particularly where the pipe is part of the adopted public sewer network.

Conclusion

Lining is a proven and efficient method for rehabilitating underground drainage and sewer pipes without the need for disruptive excavation. By installing a resin-impregnated liner that cures in place, engineers can create a durable, watertight, and structurally sound new pipe inside the existing one.

It is widely adopted across residential, commercial, and public infrastructure projects due to its speed, reliability, and long-term performance. When applied correctly, lining helps extend the life of drainage systems, reduce maintenance costs, and protect the environment from leaks and failures in ageing infrastructure.