State of Technology Report for Force Main Rehabilitation, Final ...

more appropriate to a water main where the cleaning solution can be easily re-circulated. More
information on cleaning methods and technologies is covered in Section 6.
3.4.2 Spray-on Linings. Spray-on linings have been one of the easiest methods of rehabilitating a
pressurized main when the primary objective is just to provide corrosion protection to the interior surface.
Spray-on linings are either cementitious or polymer based as shown in Figure 3-7.
With a large population of unlined CI water pipe in the US, it is not surprising that one of the more
common methods of rehabilitation has been to apply a cement mortar lining in water distribution
networks. In the UK, where water supplies tend to be more “soft” than in the US, cement mortar linings
were first supplanted by spray epoxy liners and then by polyurethane (PU) linings which today dominate
80% of the UK spray-on liner market. The main advantage of PU over epoxy is the fast 30-minute cure
time. The equipment and application are essentially the same.
3.4.2.1 Cement Mortar Linings. Cement mortar lining is not suitable for the conveyance of
aggressive (soft) water, nor would it be recommended for the rehabilitation of a sewer force main. It
involves centrifugally casting cement mortar against the wall of the pipe with sufficient velocity to
densely pack and adhere the mortar. The interior mortar lining is then mechanically trowelled to provide
a smooth surface. Cement mortar lining is most commonly used for corrosion protection in ferrous water
pipes, but is not suitable for sewer force mains.
Figure 3-7. Summary of Spray-on Lining Technologies
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