Drain relining is a proven technology with a strong track record when installed correctly. But like any construction product, it can fail, and when it does, the consequences range from reduced flow capacity to complete liner collapse. Understanding the causes of liner failure helps you choose a quality contractor and understand the warranty claim process if needed.
The quick answer
Drain relining failure is uncommon but not unknown. The main causes are: inadequate pipe cleaning before installation, incorrect resin mix ratios, premature cure in the wrong conditions, poor end termination technique, and bypassing of junctions after installation. Most failures are detectable by post-installation CCTV inspection and are the contractor’s responsibility to rectify under warranty.
What drain relining failure looks like
Liner failures fall into several categories:
| Failure type | Description | Signs |
|---|---|---|
| Delamination | Liner separates from the host pipe wall | CCTV shows liner floating, folded or collapsed into pipe bore |
| End delamination | Liner peels back at the entry or exit end | CCTV shows curled or lifted liner edge |
| Incomplete cure | Resin hasn’t fully hardened | Liner remains flexible, compresses under pressure |
| Liner wrinkle | Liner folded during installation | CCTV shows longitudinal fold reducing bore |
| Junction bypass | Branch junction not reinstated through liner | Sewage exits through unreinstated junction rather than continuing in liner |
| Liner collapse | Fully delaminated liner collapses into bore | Total blockage or severely restricted flow |
Cause 1: Inadequate pipe cleaning
The most critical pre-installation step is thorough hydro jet cleaning of the pipe. If the pipe walls retain:
- Root debris or root mat
- Scale or mineral deposits
- Grease or organic build-up
- Silt or soil from a previous collapse
…the liner cannot fully bond to the pipe wall. Areas where the liner can’t contact the wall due to intervening debris will eventually delaminate.
Prevention: Ensure the contractor performs thorough jetting and confirms a clean pipe interior on CCTV before liner installation. The pre-reline CCTV should show a clean, clear pipe.
Cause 2: Incorrect resin mix or insufficient saturation
The resin that impregnates the felt or fibreglass liner carrier must be:
- Mixed in the correct ratio (too little hardener = incomplete cure; too much = rapid exotherm and brittleness)
- Applied in the correct quantity to fully saturate the liner
- Used within its working life at the ambient temperature on the day
Field conditions, particularly on hot Central Coast summer days, can affect resin working life. If resin starts to gel before the liner is fully positioned and inflated, the result is an incompletely formed liner.
Prevention: The contractor should perform the resin mixing with calibrated equipment and account for ambient temperature. In high temperatures, refrigerated resin or UV-cure systems are preferred because working life isn’t a constraint.
Cause 3: Wrong cure method for site conditions
Different cure methods have different requirements:
- Ambient cure requires specific temperature and humidity conditions, can be affected by wet pipes, cold weather or very hot conditions
- Steam cure is faster and more reliable than ambient but requires correct steam temperature and duration
- UV cure is the most controlled method, the cure is initiated and controlled by the UV lamp pass speed, independent of ambient conditions
Using ambient cure in a high-water-table environment (common on coastal Central Coast properties near Umina, Woy Woy or Avoca Beach) risks incomplete cure in wet pipe conditions.
Prevention: Confirm with your contractor what cure method they’re using and whether it’s appropriate for your site conditions.
Cause 4: Poor end termination
The ends of the liner, where it exits the pipe at the access points, are the most vulnerable locations for delamination. End termination requires:
- The liner end to be cut cleanly at the pipe end
- The cut end to be properly sealed or trimmed flush with the pipe
- Any adhesive or mechanical termination to be correctly applied
An inadequately terminated liner end can curl back under flow pressure, creating a flow restriction or catch point for debris.
Prevention: Inspect the liner end termination on the final CCTV. The end should be flush, smooth and adhered to the pipe wall.
Cause 5: Unreinstated or poorly reinstated junctions
After the liner is installed, branch connections (junctions) that are covered by the liner must be reinstated by robotic cutter, a camera-guided cutting tool that opens the junction from inside the liner.
If a junction is:
- Not reinstated (overlooked)
- Reinstated with a hole that’s off-centre from the branch pipe
- Damaged during cutting (liner torn around the junction)
…the result is either a blocked branch pipe (nothing flows from that fixture) or a junction where the liner is weakened and susceptible to delamination around the cut edge.
Prevention: Final CCTV should confirm every junction is reinstated, correctly positioned and cleanly cut.
Detecting failure: why post-installation CCTV matters
The final CCTV inspection after relining is not a formality, it’s the quality assurance check that should be a contractual requirement. A competent contractor will conduct a post-reline camera inspection and provide footage as part of the job documentation.
What to look for in post-reline CCTV:
- Liner is smooth and adhered along its full length
- No visible delamination areas (liner should not appear to float from the wall)
- No wrinkles or folds
- Liner ends are flush and clean
- All junctions are reinstated and cleanly cut
- No voids or bypasses visible at any point
If you have not received post-reline CCTV footage, request it. If the contractor can’t provide it, treat this as a red flag.
What to do if your liner has failed
Step 1: Get independent CCTV
Before making any warranty claim, get an independent CCTV inspection that documents the failure clearly. You need:
- Footage showing the defect
- The plumber’s written assessment of the failure type and probable cause
- Comparison with the original post-installation footage if available
Step 2: Review your warranty documentation
Your warranty should specify:
- What defects it covers
- The process for making a claim
- Whether the contractor or liner manufacturer is the warranty provider
- The time frame for reporting defects
Step 3: Contact the contractor
Most warranty claims can be resolved by the contractor returning to rectify the defect. A delaminated end or an unreinstated junction is typically rectified by the contractor at no cost within the warranty period.
Step 4: Escalate if needed
If the contractor disputes the claim or is unresponsive:
- NSW Fair Trading handles disputes with licensed tradespeople
- The plumbing licence regulator (NSW Fair Trading) can take action against licensed plumbers for substandard work
- NCAT (NSW Civil and Administrative Tribunal) can hear consumer claims
Prevention checklist when hiring a drain relining contractor
| Before signing | Check |
|---|---|
| NSW plumber/drainer licence confirmed | Yes/No |
| Liner product named and specified | Yes/No |
| Resin type and cure method specified | Yes/No |
| Post-reline CCTV included in scope | Yes/No |
| Warranty terms documented (duration, what’s covered) | Yes/No |
| References or previous work evidence available | Yes/No |
See our guide to choosing a drain relining contractor for a full pre-hire checklist.
Frequently asked questions
How common is drain relining failure? Failure in correctly installed relining is uncommon. Industry data suggests that when installed by experienced contractors using quality liner products, failure rates are very low (well under 5% of installations). The cases that do fail almost always trace back to one of the installation errors described above.
Can a failed liner be removed? A rigid cured liner cannot be easily removed from inside the pipe. In most cases, a failed liner is addressed by either relining again (installing a second liner inside the failed one) or excavation and pipe replacement at the affected section.
Does the type of resin affect failure risk? Yes. Higher-quality resins (vinyl ester, two-part epoxy systems) have better adhesion characteristics and more consistent cure behaviour than basic polyester resins. For demanding environments (high groundwater, old fragile host pipes), better resin specification reduces failure risk.
If my liner delaminated after 10 years, is it still under warranty? Depends on the warranty terms. A manufacturer warranty of 25 years covering material defects would typically apply. A contractor workmanship warranty of 2 years would not. This is why reading both warranty documents before signing is important.
Can I inspect the liner myself without a camera? No. Liner condition can only be assessed via CCTV. If you have concerns about a reline done in the past, arrange a CCTV inspection to check condition.
Concerned about a pipe reline on your property? Book an independent CCTV inspection.