What is a Patching

Patching is a trenchless pipe repair technique used to restore the integrity of isolated or small sections of damaged drains, sewers or other underground pipelines. It involves the installation of a short resin-impregnated liner, known as a patch, that is positioned precisely over the area of damage and then cured in place to form a new, strong inner lining. This method is typically used where the rest of the pipe is in satisfactory condition and only a limited section requires repair.

Patching provides a cost-effective, efficient and minimally invasive solution for localised structural issues, avoiding the need for full-length lining or excavation.

When patching is used

Patching is suitable for a wide range of common pipe defects, including:

  • Cracks or fractures in pipe walls

  • Open or displaced joints

  • Infiltration or exfiltration points

  • Small voids or holes

  • Root intrusion in a specific area

  • Corrosion or wear in short sections

  • Localised collapse or deformation

It is typically applied to defects no longer than one metre and is ideal for pipes ranging in diameter from 100 mm to 600 mm, though patching systems exist for larger sizes.

The patching process

The patching method involves several key steps:

  1. Inspection
    A CCTV survey is carried out to identify the location and nature of the defect. Accurate positioning is critical for successful patching.

  2. Cleaning
    The pipe is cleaned using high-pressure water jetting to remove debris, grease, roots or other obstructions that could interfere with adhesion.

  3. Preparation
    A glass-reinforced mat or felt sleeve is impregnated with a two-part resin (typically epoxy or silicate). The patch is then wrapped around an inflatable packer.

  4. Installation
    The packer is positioned within the pipe using rods or winches so the patch aligns exactly with the defect.

  5. Curing
    The packer is inflated, pressing the patch tightly against the inner wall of the pipe. The resin cures in place, bonding the patch to the pipe and restoring structural integrity. Curing may take 30 minutes to several hours depending on resin type and ambient conditions.

  6. Removal and inspection
    Once cured, the packer is deflated and removed. A post-installation CCTV survey confirms the success of the repair.

The result is a pipe-within-a-pipe over the repaired section, extending the life of the pipeline without significant disruption.

Advantages of patching

Patching offers several benefits for property owners, utilities and contractors:

  • Avoids excavation and reinstatement costs

  • Minimises disruption to roads, pavements and landscaping

  • Provides rapid repair, often within a single working day

  • Suitable for both foul and surface water systems

  • Offers long-term durability, typically exceeding 25 years

  • Can be used as a preventative measure in high-risk areas

Patching is particularly useful for reactive maintenance, emergency repairs and situations where access is limited.

Limitations and considerations

While patching is highly effective for localised problems, it may not be suitable for extensive or systemic defects. Key limitations include:

  • Unsuitability for pipes with large-scale deformation or full-length damage

  • Limited effectiveness if multiple defects are closely spaced

  • Surface preparation is essential for proper adhesion

  • Resin selection must match the environmental and flow conditions (e.g. chemical resistance, temperature)

In cases where the pipe has widespread structural issues, full-length lining or replacement may be more appropriate.

Types of patching materials

Several materials are used for patch repairs, including:

  • Glass-reinforced polyester (GRP)
    Offers strength and chemical resistance

  • Non-woven felt
    Flexible and conformable to pipe shape

  • Epoxy and silicate resins
    Provide durable bonding and quick curing times

The choice of materials depends on pipe diameter, flow type, defect severity and system conditions.

Applications in different settings

Patching is used in a wide range of settings, including:

  • Domestic and residential drains

  • Commercial and industrial wastewater systems

  • Highway drainage and surface water sewers

  • Culverts and stormwater channels

  • Inspection chamber connections and junctions

Its flexibility makes it suitable for both planned maintenance and unplanned emergency response work.

Compliance and standards

Patching systems and methods must comply with recognised industry standards and codes of practice. In the UK, relevant standards include:

  • WIS 4-34-04 (Water Industry Specification for patch repair)

  • WRc Approved methods and materials

  • Local water company specifications

Installers should be trained and certified to ensure quality workmanship and long-term reliability.

Conclusion

Patching is a practical and reliable trenchless repair method for addressing small, isolated defects in drains and sewers. By using a resin-impregnated sleeve cured in place over the damaged section, it restores the pipe’s structural integrity quickly and without excavation.

As part of a broader toolkit of no-dig solutions, patching allows asset owners to extend the life of existing infrastructure, manage costs effectively and minimise disruption to the environment and the public. With proper assessment and installation, patching provides a high-performance solution for modern pipeline maintenance.