In a scheme to relieve such flooding in one of their catchments in Greater London, Thames Water joined forces with one of its principal contractors, Morrison Ltd, to find a way to radically alter the operational role of a 25 metre deep Victorian sewer maintenance shaft. This old, but well-maintained Victorian maintenance and materials shaft was built in the late 19th century. In the future, the shaft will be used as a combined sewer overflow backdrop shaft from a new DN750 overflow relief pipe from the local upsized sewer discharging into the Victorian Metropolitan Southern High Level Sewer No.2 some 20 metres below.

The projected lifespan of the rehabilitated shaft is at least a century; therefore Thames Water looked for a technique that was both technically mature and efficient. An unusual technical requirement was that only the middle 15 metres of the shaft were to be rehabilitated; the top and bottom five metres could be left as they were, once their stability had been checked.

Thames Water opted for the M-COATING process for the project, in conjunction with ERGELIT-KS1.The following prerequisites were crucial:

• High corrosion resistance
• High abrasion resistance
• Excellent bond with the sewer’s wet clinker brickwork
• Optimum mechanical cleaning without operatives entering shaft
• Optimum mechanical coating of walls without operatives entering shaft
• Fast, efficient operation
• Highly experienced firm
• Internationally recognised qualifications
• Compliance with all relevant safety regulations
• Compliance with all applicable norms and directives
• Excellent references

After the contract had been awarded, a technical team from Habilitas – a company specialising in ERGELIT coatings – swiftly prepared for this unique assignment. In order to ensure rapid delivery of the 2,000 or so kilograms of coating grout calculated for the job, the engineers from HERMES Technologie prescribed a somewhat larger diameter hosepipe than usual. They also increased the mixer’s output by raising the dosing screw capacity to over 16 litres per minute. The grout pump would deliver 16 litres per minute. The winch line was upgraded to a 30 metre long 4 mm thick cable. All the technical prerequisites were now in place for a successful operation.

The crew consisted of four operators to handle the 2,000 kg of ERGELIT-KS1 required for coating, and to successfully guide the 20 metre of grout delivery hose weighing in excess of 150 kg when full of mortar. As the cleaning cycle began there was a little nervousness in the air, however, this quickly disappeared. The TSSR HP nozzle was adjusted precisely to the cross-section of the shaft, and the middle section of 15metres was then jetted clean in two passes. By midday the cleaning cycle was completed and the condition of the walls was checked by CCTV.

Everything had been properly and thoroughly cleaned, the coating equipment as well as the hoses and cables were put in position and everything was connected. It was certainly unusual to be coating only the middle 15 metres of a 25 metre shaft, but it was a challenge that the highly motivated operators were happy to take on. Each man took up his position and the grout began to flow to the centrifuge motor.

After 45 minutes the centrifuge motor suddenly cut out. The experienced team thought things through and were able to solve a problem with the electrical connections. Slowly and smoothly lowering and raising the centrifugal sprayhead meant that the 25 metre deep shaft could receive a new, solid inner lining coat of ERGELIT-KS1, some 30 mm thick, between points at 5 metre and 20 metre down. At this consistency, the grout was workable for about 30 minutes.

At the edge of London, while the public remained completely unaware, another page in the history of the M-COATING and ERGELIT Dry Mortar partnership was written. All observers on the client’s side were impressed and satisfied with the nine-hour long operation.