The construction site determines the installation technology: light, steam, hot water or ambient temperature. Which curing method should ideally be used in the context of rehabilitation projects in building and site drainage?
The market for the rehabilitation of building and property drainage is currently developing dynamically. The complexity of construction sites in particular places enormous demands on pipe rehabilitation companies. Frequently there are pipe nets with many bends, dimensions and numerous inlets. As a rule, the exact course of the pipeline is not known before the measure is taken, so that pipe rehabilitation companies have to act with a high degree of flexibility.
Four different curing methods are available for rehabilitation: Light, steam, hot water and ambient temperature curing. But what are the benefits of each method? What are the disadvantages that need to be considered?
For sewer rehabilitation companies, planners and clients, the question arises as to which system with which curing should ideally be used in which application.
Fundamental difference of the resins used
With light-curing, styrene-free vinyl ester resins, significantly faster curing times are possible than with temperature-curing epoxy resins. However, styrene-free VE resins do not reliably prevent run-backs. Epoxy resins, on the other hand, have proven themselves over more than 20 years with regard to the avoidance of run-backs:
"The connections [note: pipe liner with epoxy resin] or ring gap formation [note: pipe liner with vinyl ester resin] found to be free of backward migration during curing of the pipe liner are primarily attributed to the different reaction characteristics of the resins used. Vinyl ester resins tend to shrink by up to approx. 7%, which occurs primarily during the curing phase. Epoxy resins, which are considered to have low shrinkage, typically exhibit < 1% shrinkage, which occurs in the liquid phase when the curing starts".
The BRAWOLINER® was already able to confirm in 2006 that run-backs are generally avoided when installing with epoxy resin. With all common light-curing systems, the shrinkage processes lead to the fact that a gap exists and run-backs cannot be safely avoided. For example, waste water, groundwater and roots can penetrate between the gap in between the outer side of the liner and the inner side of the old pipe.
The use of light-curing resins on construction sites for building and property drainage is particularly suitable where there are few or no inlets and outlets in the laterals. Furthermore, good accessibility in the area of the starting point and ideally also the target point (e.g. manhole, maintenance opening) is advantageous in order to be able to protect the connection area against backflow after completion of the shrinking process with e.g. sleeves or epoxy resin spatulas.
There is an almost unlimited processing time, which leads to a high level of installation safety, as the vinyl ester resins used only cure when exposed to UV or LED light. However, the use of a preliner is recommended. This prevents uncured resin from entering the groundwater via damaged areas in the soil.
The retraction speeds of the light sources are generally 0.5 - 1 meter per minute. A 30 m pipe can thus be cured in 30 to 60 minutes.
Areas of application for light-curing house connection liners are in particular:
- Storm water laterals and house laterals (without inlets)
- Rehabilitation with a limited time frame
- Laterals and connection sewers on properties (without inlets)
Hot water curing
Hot water curing is the most effective curing method. It is particularly suitable for underground and connecting pipes with a height difference of up to four metres. By using an epoxy resin, a watertight connection with the old pipe is created .
The method of hot water curing is extremely flexible. Complicated pipe connections with many bends, long supports, several dimensional jumps as well as extreme pipe geometries, connections and branches can be easily rehabilitated. During curing, an even heat distribution is created in the liner, since the heat transfer medium is available everywhere - water finds its way. The curing time is generally two to four hours for liner lengths of up to 50 m.
Hot water curing is not suitable for larger height differences or vertical pipes. Depending on the length and dimension of the liner, longer filling times may occur.
Areas of application for hot water curing house connection liners are in particular:
- Complicated property drainage networks
- Long laterals with numerous inlets and outlets
- Laterals and connections sewers with several dimensional jumps, extreme line geometries and many bends
Steam curing and ambient temperature curing
Steam curing and curing at ambient temperature are particularly suitable for pipes with a large gradient difference, such as downpipes and in the in-house area, but earth-laid pipes can also be rehabilitated using these methods. The use of an epoxy resin basically results in a connection with the old pipe that is free of backflow.
Both curing methods can be used extremely flexibly: even many bends, long pipe supports and extreme pipe geometries pose no problem during rehabilitation. Branches, connections and several dimensional jumps can also be rehabilitated.
The curing time during steam curing is usually one to three hours for holding lengths of up to 50 m and the filling time of the liner is only brief. In order to avoid delays in curing due to condensation water, a safe drainage must be ensured.
When curing at ambient temperature, no additional equipment is required for curing. This results in lower investment and acquisition costs. In addition, there is no additional effort on site to accelerate the curing process. However, long curing times may occur, as these depend on the ambient temperature.
Areas of application for steam-curing and at ambient temperature curing house connection liners are in particular:
- In-house rehabilitations
- Pipes with large gradient differences (e.g. downpipes)
- Laterals with several dimensional jumps, extreme pipe geometries and many bends
The requirements and challenges on construction sites for building and site drainage are enormous for pipe rehabilitation companies: pipe networks with complicated drainage lines, many bends and dimensional jumps often exist. Often the exact course of the pipeline is not known before the measure is taken, so that a high degree of flexibility is required on site. Sewer rehabilitation companies must be able to react flexibly and quickly without losing construction time.
With a pipe liner for all curing methods (ambient temperature, water, steam and light) this flexibility is given, since every situation and requirement can be dealt with individually. It is important to emphasize that the choice of the installation technique or curing method depends on the structure and condition of the sewer, the pipe and the pipe network and the boundary conditions on site. The requirements of the construction site determine the installation technology - not vice versa. Here, particularly planning engineering offices and tendering parties are required to demand the best installation technology in order to achieve optimum results for their clients.
 Expert report: Accompaniment of sample construction sites - Testing for freedom from backward migration on different house connection liner systems, Report No. 19-210-02264-SB, p. 10.
 s. Ref. CP308/1/2, Cured-in-place Pipe Leaktightness Test, WRc, Dezember 2006.
 s. Expert report: Accompaniment of Sample Construction Sites - Testing for Freedom from Hinder Migration on Different House Connection Liner Systems, Report No. 19-210-02264-SB, p. 10
 s. Leddig-Bahls, Susanne 2019. Sanierung von Rohrleitungen innerhalb von Gebäuden. 3R 04-05 2019.