Peel Harbour Isle of Man, UK

THE PROJECT

In 2022, Gunform International Limited, a SCA member based in the North-west of England with over 35 years of spray experience, were approached about a marine repair project. The Department of Infrastructure had earmarked the sea wall in Peel on The Isle of Man for refurbishment, as the bull-nosed arris on the promenade had slowly been eroded, with years of chloride ingress taking its toll on the reinforced concrete form. The repair of sea walls, especially those incorporating a promenade, must be both functional and high performing. There is also an aesthetic demand on their refurbishment which goes beyond that of many other types of infrastructure repair. The initial plan was to remove the defective concrete and replace the bull-nose with a formed pre-cast block – something which would have been costly and involved a far greater removal of existing concrete from the existing wall. This is where Gunform saw an opportunity to use sprayed concrete.

THE SOLUTION

An excavator was used to remove all the existing defective concrete, and the periphery of the repair areas were prepared with hand-tools to ensure no feather-edging at the existing concrete interface, in line with BS EN1504 standards. The entire repair area was then high-pressure washed to remove all surface chlorides and organic matter. New reinforcement was introduced in the form of rebar cages connected with chemical anchors. Fosroc’s Renderoc DSR (Rapid-set) was adopted as the dry-spray mortar for the initial bulk coverage of the rebar with Renderoc DS then being used for concrete reinstatement closer to the finished surface. The reason for this was down to setting times – the technique adopted by Gunform was to support and form the outer edge of the repairs using timber shutters, and then strike the shutters within a time frame. This allowed the finer hand-skills of closing off the surface of the concrete by steel float. Renderoc DS stays open longer to allow more time to influence surface finishing.

THE BENEFITS

The resulting repairs achieved an aesthetic quality befitting of a structure in the public view and will perform to the high standard expected of works undertaken in the public realm. Furthermore, this project is a fine example of a skilled contractor taking an alternative view on a repair solution based on their own knowledge of a materials capabilities. Renderoc DSR’s extremely fast early-set allows layers to be built up in multiple passes, while the underlying layer sets in around ten minutes. It still conforms to the performance specification of an R4 rated mortar within BS EN1504-3 and the fibre-reinforced mortar achieves better cohesion in service, to reduce the costly ‘rebound’ wastage associated with the dry-spraying process.