Understanding the Importance of Proper Pipe Relining

Pipe relining has transformed the way plumbing professionals and property owners address damaged drainage and sewer lines. This trenchless technology allows for the restoration of pipes from within, eliminating the need for disruptive excavation. However, the success of a relining project depends heavily on avoiding a series of common mistakes that can compromise the integrity and longevity of the repair. Whether you are a seasoned contractor or a homeowner overseeing a project, understanding these pitfalls is essential for achieving a reliable, long-lasting result.

The process involves inserting a resin-impregnated liner into the existing pipe, inflating it against the pipe walls, and allowing it to cure. If any step is overlooked or executed poorly, the liner may fail prematurely, leading to recurring blockages, leaks, or even complete structural collapse. This article provides a comprehensive, step-by-step guide to the most frequent errors encountered during pipe relining procedures and how to avoid them.

Comprehensive Pre-Installation Assessment

Before any liner touches the pipe, a thorough assessment of the existing system is non-negotiable. Skipping or rushing this phase is one of the most common and costly mistakes. The goal is to understand the exact condition of the host pipe, including its material, diameter, slope, and the extent of damage.

The Critical Role of CCTV Inspection

A closed-circuit television (CCTV) inspection is the gold standard for evaluating pipe interiors. This step allows technicians to identify blockages, root intrusions, offset joints, cracks, and deformations. Without a clear video record, decisions about liner type and installation method are made in the dark. Always insist on a full CCTV survey that covers the entire length of the pipe to be relined, including any lateral connections.

Common CCTV Oversights

  • Not inspecting the full pipe length, especially remote sections
  • Failing to note pipe ovality or significant deflection that may prevent liner insertion
  • Ignoring the presence of debris or standing water that can interfere with resin adhesion
  • Overlooking previous repair patches or misaligned sections

External resources such as NASSCO (National Association of Sewer Service Companies) provide standardized inspection codes that should be followed for consistency and accuracy.

Addressing Root Intrusions and Blockages

Tree roots are a leading cause of pipe damage. During relining, any roots that have penetrated the pipe must be mechanically removed before liner insertion. Simply cutting them with a rooter may leave remnants that degrade over time, causing new obstructions or interfering with the liner's bond. Hydraulic or mechanical cutting followed by high-pressure cleaning is recommended. Similarly, any solid blockages, such as grease or sediment, must be completely cleared. Failing to do so will result in a liner that cannot seat properly, creating weak spots or voids.

Crucial Cleaning Protocols

Even after removing visible blockages, the pipe walls must be scrupulously clean. Any grease, slime, or mineral deposits will prevent the resin from bonding permanently to the host pipe. High-velocity water jetting with appropriate nozzles is the standard cleaning method. In some cases, mechanical scraping or chemical pre-treatments may be needed. Never assume a pipe is clean enough—verify with a post-cleaning CCTV.

Selecting the Right Liner and Resin System

Using the wrong materials is a recipe for failure. The liner and resin must be matched not only to the pipe material but also to the environmental conditions, such as temperature and chemical exposure. Mistakes in material selection can lead to poor adhesion, incomplete curing, or a liner that is either too rigid or too flexible for the application.

Matching Liner Type to Pipe Material and Condition

Most current pipe relining systems fall into two main categories: cured-in-place pipe (CIPP) and pull-in-place (PIP) liners. Within CIPP, the liner fabric can be polyester, felt, or fiberglass, each with different tensile strengths and elongation properties. For example, fiberglass liners offer higher structural strength and are better suited for pipes with significant deformation or live loads (e.g., under roads). Polyester liners are more common for residential gravity sewers. Always consult the manufacturer's data sheets and structural design guide to select a liner that meets the required pressure or load class.

Key Material Selection Factors

  • Pipe material: Is the host pipe PVC, clay, cast iron, or concrete? Different liners and resins bond differently to each substrate.
  • Pipe age and condition: Older, brittle pipes may require a more flexible liner to accommodate minor movement.
  • Chemical environment: Industrial or commercial drains may require epoxy resins with higher chemical resistance.
  • Temperature range: Curing times and resin viscosity are heavily temperature-dependent. Hot weather speeds up cure; cold weather slows it or may require heated cure.

Refer to ASTM F1216 for standard practice for CIPP installation in non-pressure pipes. Following these standards helps ensure material compatibility and performance.

Prioritizing Certified and Tested Products

Not all liners on the market are created equal. Choose products that carry third-party certifications and have been tested for long-term performance, such as those listed by the NSF International for potable water contact if applicable, or those that meet ASTM or EN standards. Avoid bargain materials that lack documentation—they often fail within a few years, negating any initial savings.

Mastering the Installation Process

Even with perfect materials, improper installation is a leading cause of liner failures. This step demands meticulous attention to detail, from resin mixing to liner inversion and curing. Rushing through any phase increases the risk of defects.

Accurate Resin Mixing and Impregnation

The resin and hardener must be mixed in the exact ratio specified by the manufacturer. Using a scale to weigh components is far more reliable than volumetric guesswork. Insufficient hardener leads to incomplete cure (a sticky liner), while excess hardener can cause the resin to gel too quickly, preventing proper saturation of the fabric. After mixing, the resin must be evenly distributed throughout the liner. Vacuum impregnation or controlled roller methods are preferred over hand-brushing, especially for large-diameter liners.

Common Mixing Errors

  • Inaccurate measurement of resin and catalyst
  • Mixing too much material at once, causing premature exotherm and waste
  • Using resin past its shelf life or storage temperature range
  • Failing to wet out the liner completely, leaving dry spots that become weak points

Proper Liner Insertion and Inversion

Whether using the inversion method (air or water) or pull-in-place, the liner must be inserted without twisting, bunching, or excessive stretching. A twisted liner will create wrinkles that reduce flow capacity and can trap debris. Ensure the liner is correctly oriented—the resin-impregnated side must face the host pipe wall for adhesion. In inversion methods, monitor pressure and speed to avoid sudden surges that can burst the liner or blow out the inversion bladder.

Control of Curing Conditions

Curing is the most critical phase. The liner must be held firmly against the pipe wall until the resin reaches its full strength. Using hot water, steam, or UV light—depending on the system—requires precise temperature and duration control. Never cut the curing time short based on estimates; always use the manufacturer's minimum times, and if in doubt, extend the cure. In cold environments, the curing water may need to be preheated and the pipe insulated. A common mistake is to assume that "feeling" the liner's surface temperature indicates internal cure—this is unreliable. Use temperature sensors or cure logs.

Installation Pitfalls to Avoid

  • Inadequate liner expansion: The liner must be pressed tightly against the pipe walls to eliminate voids. Low inflation pressure or short cure time can leave gaps.
  • Improper sealing at connections and laterals: For lateral relines, the connection point must be precisely cut and sealed. Open or poorly sealed laterals allow groundwater infiltration and future blockages.
  • Rushing the process: Every step from resin mix to final cure takes time. Trying to finish a job in one day when conditions require two is a recipe for failure.

Many manufacturers provide detailed installation manuals and training. Organizations like the Trenchless Technology magazine also publish case studies and best practices that highlight common mistakes and their solutions.

Thorough Post-Installation Verification

The work is not finished when the liner is cured. Skimping on final inspection is a mistake that can allow defects to go unnoticed until a leak or blockage occurs. A comprehensive post-installation verification should include both visual inspection and functional testing.

The Essential Final CCTV Survey

After curing, run a CCTV camera through the relined pipe. Look for:

  • Wrinkles, folds, or delamination: The liner should form a smooth, continuous surface. Any deformation indicates that the liner did not fully expand or that the resin sagged during cure.
  • Misaligned joints or gaps: The liner should be flush with the pipe opening at each end and at laterals. Gaps invite root intrusion.
  • Blistering or air pockets: Air trapped between the liner and host pipe can lead to detachment.
  • Improper lateral connections: The opening to a lateral branch must be cleanly cut and sealed; excessive resin intrusion into the lateral is also a defect.
Fix any issues immediately—delaying remediation often requires cutting out the liner and starting over.

Pressure Testing for Leak Integrity

While not always required for gravity sewers, a low-pressure air test per ASTM standards provides additional confidence. For pressure pipes (e.g., force mains), a hydrostatic pressure test is mandatory. A positive test result verifies that the liner can withstand operating conditions without leaking. Many failures occur because contractors assume the liner is watertight without testing, only to discover infiltration during the next rain event.

Documenting the Results

Always create a final report that includes pre- and post-installation CCTV footage, material certifications, curing logs, and test results. This documentation serves as a warranty record and can be invaluable if future issues arise. It also demonstrates professional workmanship to clients.

Additional Pitfalls That Compromise Long-Term Performance

Beyond the installation steps, several overarching mistakes can undermine a project. Being aware of these can save time and money.

Neglecting to Bypass Flow During Cure

During relining, the pipe being worked on must be taken out of service. If wastewater or stormwater is allowed to flow during resin cure, it can cool the liner unevenly, wash away uncured resin, or cause the liner to float or collapse. Always set up a reliable bypass pumping system and verify that it can handle peak flow for the entire curing duration.

Ignoring Site-Specific Conditions

Soil type, groundwater level, and pipe depth all influence liner behavior. In areas with high groundwater, the external hydrostatic pressure can collapse an improperly cured liner. In soils with sulfates or other aggressive chemicals, the resin must be specially formulated. Adapt the relining plan to site conditions rather than using a one-size-fits-all approach.

Failing to Obtain Proper Training

Pipe relining is a specialized skill. Even experienced plumbers should invest in manufacturer-certified training programs. Untrained crews are the primary source of most mistakes—from resin handling to equipment operation. Many material suppliers offer training courses that cover common mistakes and how to avoid them. Never assume that watching a few YouTube videos is sufficient.

Conclusion: A Systematic Approach to Flawless Relining

Avoiding common mistakes in pipe relining requires a systematic, disciplined approach at every stage: assessment, material selection, installation, and verification. By dedicating time to proper CCTV inspection, thorough cleaning, careful material choice, precise resin mixing and curing, and rigorous post-installation testing, you can ensure a durable, watertight liner that lasts for decades. The upfront effort pays off in reduced callbacks, satisfied customers, and a reputation for quality work.

Remember that pipe relining is not a shortcut; it is a sophisticated repair method that demands the same level of care as a new pipe installation. Stay informed about industry developments, follow standards, and never cut corners. For further reading on industry best practices, refer to the Plumbing World resource directory and the Sewer Vac blog for case studies on successful relining projects that avoided these common pitfalls.

Ultimately, the cost of correcting a failed reline—both monetary and reputational—far exceeds the cost of doing it right the first time. Follow these guidelines to avoid the most frequent mistakes and deliver a pipe repair that truly stands the test of time.