A top hat liner seals the connection between a lateral drain or sewer and a vertical pipe connected to it. It gets its name from its shape. McAllister uses various top hat liners – most commonly Trelleborg’s EPROS® LCR System or Hächler's EL300/600 grout injection lateral repair unit.

Top hat liners use similar technology as our CIPP liners. They are made of polyester and infused with a resin that, when cured, forms an impermeable bond with the host pipe. Our technicians use a specialised tool known as a “packer” that pushes the liner into place with an extendible “finger”.

We use top hat liners to:

  • prevent leaks and groundwater pollution out of faulty pipe connections.

  • prevent groundwater infiltration from washing the soil away from a sewer system, which would otherwise create voids around connections.

  • repair connections that have come loose due to poor installation, temperature fluctuations, or heavy traffic.

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Our top hat liner service teams have a few requirements before they can get to work. They must conduct a preliminary survey to assess the damage and measure the host pipe and lateral connections. They also need data about the probable flow rates to provide over-pumping or temporary sealing. They need safe access and a working area around the chamber.

Our technicians prepare the packer off-site by infusing the top-hat liner with resin, wrapping it around the packer, and loading it into the van. Once on-site, our technicians conduct a brief CCTV survey to determine the precise location of the damage. They use this information to guide the packer into place, monitoring their work with an onboard CCTV link. The packer extends and inverts the top hat liner, while the finger ensures that it bonds with all the pipe connection’s surfaces. The team then pumps extra resin into any cavities, especially in the damaged area. This extra resin creates a permanent bond between the top hat liner, the host pipe, and the lateral connection.

The packer remains in place while the resin cures – the specific resin mix determines how long this takes. Once the resin is completely cured, our technicians deflate the packer, retract the finger, and remove the equipment from the pipe. Finally, they check their work with a final CCTV survey and save the data for our project report.

McAllister was one of the UK’s first environmental services firms to adopt top hat lining systems, and we have done thousands of these in numerous geographical locations. Many of our staff have the relevant training and experience to install top hat liners, and we keep two dedicated top hat liner teams on call at all times. We enjoy a close working relationship with Trelleborg, the EPROS system manufacturer, and they provide comprehensive training and support for our team.

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