Sunday, June 16, 2024

The Differences in Curing Systems

RSM explores the differences between curing methods in CIPP Lining

First introduced in 1971, CIPP Lining has become the most used method of Sewer Rehabilitation over the last 50 years. CIPP’s rapid development has led to the swift expansion of different curing methods – ambient cure, hot cure, steam cure, UV cure, and UV LED cure.

This article aims to explore the differences between curing methods and their various advantages and limitations. Probably the most used curing method is ambient cure. Ambient curing essentially means that once the liner has been installed, it is left to cure in the ambient temperature.

The liner for ambient cure installations must be impregnated by the engineer on site before being dragged or inverted into place, there is no possibility for factory impregnation due to the working times of the resin. Ambient cure lining is a relatively fast installation process with limited equipment needed and a small on-site team required, meaning there is a small on-site footprint.

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For larger diameter, longer length jobs, ambient cure is not the most practical method of installation – it is generally recommended that ambient cure installations only go up to 225mm in diameter. There are also limitations to the length of liners that can be installed due to the time constraints of the resin. However, the resin can be manipulated for longer or shorter cure times – RSM Lining Supplies supply a range of resins suitable for ambient cure (polyester, epoxy, and silicate). Ambient cure is popular for use with shorter, small diameter installations due to the lower price tag, small on-site footprint, and ease of installation.

Hot cure, as the name suggests, involves the addition of heat to cure the liner after it has been inverted or dragged into the pipe – this is done with the use of a hot water boiler. Ordinarily hot cure liners are factory impregnated and delivered to site in refrigerated transport (a service RSM provide!). The boiler heats the water to around 80 degrees and this is then circulated through the liner via a hose until the liner is cured (generally this takes around 3 – 4 hours).

The addition of heat speeds up the curing of the liner exponentially and is typically used for jobs that are longer in length and larger in diameter – RSM’s largest hot cure impregnation to date was for a 1300mm diameter liner that was successfully impregnated by RSM and installed by their customer back in 2019.

The hot cure methodology is incredibly popular industry-wide but does of course come with some drawbacks as it leaves a relatively large installation footprint due to the requirement of a water source and tankers.

Hot cure is still a reasonably low-price curing process after the initial cost of the hot water boiler and speeds up the cure time for the contractor. There is also the possibility of using chemically resistant resins with hot cure (such as vinylester and epoxy), and it is the only curing system suitable for curing pressure pipe liners (such as RSM’s Fero Force). Hot cure also counteracts infiltration by using the weight of the water.

Similarly to hot cure, steam cured liners are generally factory impregnated before being delivered to site. Steam cure also requires less water supply and access as there is no tanker required to dispose of wastewater as is required with a hot water boiler, reducing the on-site footprint and cost.

There is however the added potential of ‘cold spots’ when steam curing if there is pooled water within the pipe or laterals, and on-site health and safety guidelines must be stringent due to the large quantity of hot steam being emitted from the boiler. A larger compressor than that needed for hot cure is also required.

UV cure was developed back in the 1990’s and its popularity has grown rapidly over the years; it has a relatively quick cure time and a high strength characteristic (although there is no adhesion to the pipe, so it does not give a leak tight finish). UV liners are also available in diameters up to 1600mm and above, so it is an incredibly useful curing method for larger diameter liners.

The liner is pulled through the host pipe using a winch and UV lights are run through the pipe, prompting the liner to cure. As the UV bulbs are filament bulbs, they have a limited lifespan and will require replacing relatively regularly which can become costly. Caution should also be taken when using the UV curing method due to the heat that can be generated by the bulbs.

In general, there is a higher cost associated with UV cure than ambient, hot cure & steam. It is also time consuming to set up, a large installation team is required to successfully complete the installation, there is a very large plant footprint, and larger compressors and generators are required than for hot cure and steam cure. UV Cure also does not allow for any blind shot installations or installations with bends.

An extension of UV cure is the relatively new technology of UV LED. UV LED cure brings with it all the good qualities of standard UV cure in a smaller package. Although the initial system set up can be costly, it does work out cheaper in the long run as the UV LED cure methodology requires less power and energy to cure a liner than traditional systems, and the curing process does not require water meaning there is no requirement for heavy equipment. This reduces the contractor’s on-site footprint and any potential impact on residential properties.

The lightweight and portable equipment used for UV LED curing (such as the Sewertronics Speedylight+ System) means access to small working areas is achievable. This is incredibly convenient when working in limited access areas such as residential neighbourhoods, when taking a large boiler to site could be problematic. UV LED curing dramatically shortens the time required for pipe rehabilitation, making it an incredibly efficient curing method.

The variety of curing methods available across the CIPP industry allows contractors to tailor their No-Dig solutions to each specific job. Although there are strengths and limitations to all, their different suitability’s and applications make them all worthy methods to consider when planning a repair. For advice on which curing methodology is most suitable for you, get in touch with the RSM Sales Team on 01709 864271 or send an email over to

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Trenchless Works bringing you balanced journalism, accuracy, news and features for all involved in the business of trenchless and no-dig from around the world

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