What is a Patch lining

Patch lining is a widely used trenchless method for repairing localised damage in underground drainage and sewer pipes. It involves placing a short section of resin-impregnated liner inside the existing pipe to cover cracks, fractures, or displaced joints. Once cured, the liner bonds to the inner wall, restoring the structural integrity and watertightness of the pipe.

This technique is particularly suited to situations where the rest of the pipe is in good condition and only a small area requires reinforcement. It is faster and less invasive than full pipe replacement and significantly more cost effective than excavating to access the fault directly.

When patch lining is used

Patch lining is ideal for repairing isolated defects. These can include:

  • Cracks caused by ground movement or pressure

  • Displaced or open joints

  • Minor root ingress

  • Small holes or wear spots

  • Fractures in older clay or cast iron pipework

The method is commonly used in residential, commercial and municipal drainage systems, especially in areas where access is restricted or where excavation would be costly or disruptive.

Benefits of patch lining

Patch lining offers a number of clear advantages over traditional repair methods:

  • No need for digging or breaking surfaces

  • Quick to install, often within a few hours

  • Compatible with most common pipe materials

  • Long service life, typically over 50 years

  • Low impact on surrounding structures and environments

  • Reduced risk of future infiltration or leakage

Because it can be installed through existing access points such as manholes or rodding eyes, patch lining avoids the need for permits, surface restoration or major groundwork.

How the process works

The patch lining procedure involves a series of carefully controlled steps to ensure the repair is durable and accurately positioned.

  1. Inspection
    A CCTV drain survey is carried out to identify the location and extent of the damage.

  2. Cleaning
    The pipe is cleaned using high-pressure water jetting or mechanical tools to remove debris, scale or roots.

  3. Preparation
    A short section of liner, usually made of fibreglass or non-woven material, is cut to size and saturated with a resin. This resin may be epoxy, silicate or polyester depending on the application.

  4. Installation
    The liner is wrapped around an inflatable packer and inserted into the pipe using push rods or ropes. The packer is positioned so that the patch covers the damaged section precisely.

  5. Curing
    The packer is inflated, pressing the resin-soaked patch firmly against the pipe wall. After a set curing time, the resin hardens and bonds with the host pipe.

  6. Completion
    The packer is deflated and removed. A final CCTV inspection is performed to confirm the success of the repair.

Technical considerations

Patch liners are typically between 0.5 and 1.5 metres in length. They can be installed in pipes ranging from 75 mm to 300 mm in diameter, though custom solutions exist for larger sizes. The repair adds a small internal thickness to the pipe, but this usually has a minimal effect on flow rates.

To ensure long term performance, the following factors must be considered:

  • Pipe must be clean and free of active flow during installation

  • Resin type must match expected chemical exposure and temperature

  • Proper curing time must be observed based on resin and ambient conditions

  • Liner and packer sizes must match the pipe diameter precisely

Only trained personnel should carry out patch lining to avoid issues such as poor adhesion, misalignment or incomplete curing.

When patch lining is not suitable

While highly effective for localised defects, patch lining is not suitable in all cases. It may not be appropriate if:

  • The pipe is extensively collapsed or deformed

  • There are multiple defects over a long section

  • There is no access for equipment or packer insertion

  • Pipe diameter varies significantly near the repair area

In such cases, full length lining, pipe bursting or excavation may be required instead.

Compliance and industry standards

In the United Kingdom, patch lining must meet standards set by the Water Research Centre and conform to Water Industry Specification WIS 4-34-04. Repairs must not reduce the structural integrity or flow performance of the drainage system. Responsible installers should provide a full CCTV report and guarantee on completion.

Conclusion

Patch lining is a practical, efficient and cost effective method of repairing isolated faults in underground drainage systems. It eliminates the need for excavation, reduces downtime and offers long term structural and hydraulic performance.

When used appropriately, it can restore a damaged section of pipe to near-original condition, extend the life of existing infrastructure and prevent the need for more invasive and expensive repairs in the future. For engineers, property managers and homeowners alike, patch lining is an essential tool in modern drain maintenance.