When you get a drain relining quote, the resin type used is one of the most important technical variables, but it’s rarely explained. The resin is what transforms a saturated felt or fibreglass tube into a rigid, structural pipe. Different resin chemistries have different strength, longevity, chemical resistance and cost profiles. Here’s what you need to know to ask the right questions.
The quick answer
Epoxy resin is the standard and preferred choice for residential sewer relining. It has excellent adhesion, chemical resistance and long service life. Polyester resin is cheaper but less durable and not recommended for sewer applications. Vinyl ester is the highest-performing option, longer life, superior chemical resistance, but costs more. For most Central Coast residential jobs, a quality epoxy resin system is the right specification.
The three main resin types in drain relining
1. Epoxy resin
Epoxy is a two-component thermoset resin: a resin component and a hardener, mixed in a precise ratio immediately before use.
Properties:
- Excellent adhesion to a wide range of pipe substrates (clay, AC cement, PVC, cast iron)
- Good chemical resistance to sewage, hydrogen sulphide and typical groundwater chemistry
- Moderate cure time, ambient cure in 12-24 hours at 20°C, or accelerated with heat or UV
- Good long-term flexibility (resists cracking under thermal cycling)
- Expected service life: 50-70 years in residential sewer conditions
Limitations:
- More sensitive to mixing ratio errors than polyester, incorrect hardener ratio results in incomplete cure
- Working life is temperature-sensitive, hot days shorten working time
- Higher raw material cost than polyester
Typical use: Standard residential sewer and stormwater relining. The default choice for most Central Coast residential jobs.
2. Polyester resin
Polyester resin is a one-part system (or catalyst-activated system) that’s been used in drain relining and fibreglass manufacture for decades.
Properties:
- Cheaper than epoxy
- Faster ambient cure in some formulations
- Adequate for some stormwater applications
Limitations:
- Significant shrinkage during cure, polyester shrinks as it cures, which can cause the liner to pull away from the pipe wall (delamination risk)
- Inferior adhesion compared to epoxy, particularly to damp pipe surfaces and old clay
- Poor resistance to hydrogen sulphide, sewer gas will degrade polyester liners over time
- Shorter service life in sewer applications, typically 25-40 years vs 50-70 years for epoxy
- Styrene odour during cure, a VOC (volatile organic compound) that requires ventilation
Verdict: Not recommended for sewer drain relining. Acceptable for some stormwater applications where chemical exposure is lower, but even here, epoxy is preferred.
3. Vinyl ester resin
Vinyl ester is a hybrid between epoxy and polyester, it combines the chemical performance of epoxy with some of the processing characteristics of polyester.
Properties:
- Superior chemical resistance, the best of the three types, particularly resistant to strong acids and hydrogen sulphide
- Excellent long-term durability, expected service life of 70-100 years in demanding environments
- Low shrinkage, minimal delamination risk
- Good adhesion to most pipe substrates
- Better temperature resistance than standard epoxy
Limitations:
- Highest cost, significantly more expensive than epoxy
- Still emits styrene during cure (less than polyester, but present)
- Requires more careful handling than epoxy
Typical use: Commercial applications, aggressive environments (industrial drainage, high-sulphide sewer systems, marine environments), and projects where maximum service life is the priority.
Comparison table
| Property | Epoxy | Polyester | Vinyl ester |
|---|---|---|---|
| Adhesion to wet surfaces | Excellent | Poor | Good |
| Chemical resistance (sewage) | Good | Poor | Excellent |
| Cure shrinkage | Very low | High | Low |
| Delamination risk | Low | High | Very low |
| Expected service life (sewer) | 50-70 years | 25-40 years | 70-100 years |
| Cost | Moderate | Low | High |
| Suitable for sewer relining | Yes | No | Yes |
| Suitable for stormwater | Yes | Marginal | Yes |
| Styrene odour during cure | No | Yes | Reduced |
Liner carrier materials: felt vs fibreglass
The resin is impregnated into a carrier material, either a felt (non-woven polyester felt) or a fibreglass reinforcement. This affects the liner’s structural performance independent of the resin choice.
| Carrier type | Structural properties | Best with |
|---|---|---|
| Non-woven polyester felt | Good for standard residential | Epoxy or vinyl ester |
| Fibreglass composite | Significantly stronger, more rigid | Epoxy or vinyl ester |
| Glass-reinforced plastic (GRP) | Highest structural performance | Vinyl ester |
For most residential applications (100-150 mm diameter, standard depths), a felt carrier with epoxy resin is adequate. For larger diameter pipes, greater depths, or commercial applications, fibreglass or GRP carriers with vinyl ester resin provide superior performance.
Cure methods and their effect on resin performance
The cure method affects how reliably the resin reaches full cure:
| Cure method | How it works | Resin compatibility | Performance |
|---|---|---|---|
| Ambient cure | Cures at ambient temperature over 12-24 hours | Epoxy, some vinyl ester | Moisture and temperature dependent |
| Steam cure | Steam applied through bladder, 60-90°C | Epoxy, vinyl ester | Faster and more reliable than ambient |
| UV cure | UV light lamp drawn through liner | Epoxy systems with photoinitiator | Most controlled, moisture-independent |
UV cure with epoxy resin is considered the industry best practice for residential drain relining. It’s fast (15-40 min for a standard residential run), controllable, and produces consistent, high-quality cure regardless of ambient conditions. This matters especially on the Central Coast where high-humidity conditions and wet pipes (particularly near the coast) can affect ambient cure performance.
What to ask your contractor
Before signing a quote for drain relining, ask:
- What resin type are you using (epoxy, polyester, vinyl ester)?
- What is the liner carrier material (felt, fibreglass)?
- What is the cure method (ambient, steam, UV)?
- What is the liner manufacturer and product name?
- Can you provide the technical data sheet for the liner product?
Any contractor who can’t answer these questions or who uses polyester resin for sewer relining should prompt you to consider alternative quotes.
See our choosing a drain relining contractor guide for a full pre-hire checklist.
Coastal environment considerations
The Central Coast’s coastal conditions, high humidity, salt-laden air, elevated groundwater, are relevant to resin performance:
- Epoxy adhesion to pipe walls is minimally affected by damp conditions, but very wet pipes benefit from UV cure which bypasses moisture sensitivity
- Vinyl ester’s superior chemical resistance makes it a strong choice for properties near estuaries or with corrosive groundwater chemistry
- High water table environments (Umina, Woy Woy, foreshore areas) particularly benefit from UV-cure epoxy or vinyl ester liners
Frequently asked questions
Is epoxy resin safe once it’s cured inside a sewer pipe? Yes. Fully cured epoxy is chemically inert and FDA-approved for contact with drinking water (when properly formulated). Once cured, it doesn’t leach into the surrounding soil or water. The resin is only reactive in its uncured, liquid state.
How can I tell what resin my contractor used if it’s already installed? Ask for the job documentation, the liner product specification should be on the installation record. The liner itself (once cured) can be tested by a specialist, but the most practical approach is to ensure you have product documentation before the contractor leaves.
Does a cheaper polyester-resin reline invalidate the warranty of a more expensive system if done later in the same pipe? Two different liners can coexist in the same pipe system if they’re in different sections. The performance of each liner depends on its own resin specification. A polyester liner in one section doesn’t affect a correctly installed epoxy liner in another section.
Are there any environmental concerns with drain relining resins? Uncured resins must be handled as hazardous materials and disposed of correctly. Once cured, the liner is inert. Styrene emissions from polyester and vinyl ester during cure are the main workplace health concern, proper ventilation and PPE are required. After cure, there are no ongoing emissions.
Do all drain relining liners in Australia have to meet Australian Standards? CIPP (cured-in-place pipe) liners are covered by AS/NZS 2566 (Part 1: Buried flexible pipelines, Part 2: Installation). Products sold by reputable manufacturers for Australian use should comply with these standards. Ask your contractor for compliance documentation.
Want to know exactly what liner product will go into your pipes? Get a detailed quote and specification.