Spray concrete defends Nothe Fort at Weymouth Harbour
High performance spray repair concrete by Saint-Gobain Weber has been used to fortify the sea wall that acts as a coastal defence to Nothe Fort at Weymouth Harbour, Dorset.
Built between 1860 and 1872 by 26 Company of the Royal Engineers to protect Portland and Weymouth harbours, Nothe Fort became an important Royal Navy base especially in World War II. The fort’s first stage of construction was the sea wall which allowed a level site to be formed on the sloping ground at the end of Nothe Peninsula.
The Grade II listed fort was abandoned in 1956 and in 1961 it was sold to Weymouth and Portsmouth Borough Council. The property remained unoccupied and quickly became a victim of vandalism before falling into a state of dereliction. Over the many decades of continuous exposure to sea water and tidal action, work to reinstate the concrete harbour wall became essential. Main contractor APA Concrete Repairs Limited took on this extensive project which was completed in May 2017. APA Concrete Repairs is an experienced multi-disciplined specialist structural repair and refurbishment contractor.
Les Wallis, southern area director for APA Concrete Repairs, said: “This is the second project carried out by APA at the Nothe Fort for Weymouth and Portsmouth Borough Council. We had already added protection to the pier wall but this groyne wall had very serious tidal damage.” When the debris had been cleared it was evident at low tide that large pockets had been drilled into the wall foundations.
webercem spray DS and webercem spray RS were expertly applied by David Porter-Hallett who explained: “The Weymouth groyne wall had very bad erosion above the high water line but even worse damage with sections of the foundations which had been washed away by tidal erosion”.
“Access to the site was restricted and the project had to be run in tandem to benefit from the fall of spring tides. At the same time visitors were enjoying their spring holiday time in Weymouth during which we had to closely manage the site. With scaffolding in place, high pressure jetting cleaned the exposed surfaces above the waterline which we sealed with mesh and webercem spray DS. This product is ideal as it has low rebound on application which helps us eliminate water fouling. We can quite easily catch the small amount of dropped material so it does not pollute the sea water where fish are present.”
Having removed the scaffold, phase II proved to be an even bigger challenge. “Working in the low tide zone gave us just two hour windows of operation,” continues David. “Staff in waders had to wear full safety suits and be constantly attached to manned safety lines. Rocks on the seafloor made this difficult and prevented operation by boat.
“The high pressure water jetting removed vegetation and rubbish and exposed the half metre deep holes which had to be filled which is where we took advantage of the rapid setting benefits of webercem spray RS. It enabled us to build up these repair layers to maximum thickness in the two hour tidal windows. Altogether we used 16 tonnes of webercem spray DS on the upper surfaces and a further five tonnes of webercem spray RS on the foundation areas. The low rebound qualities of webercem spray RS allows us to ensure a safe environmental protection system to catch the small amount of dropped material.”
“We are confident that we have given the groyne a minimum extended life of 50 years. We really rely on the Weber range of technical mortars for ease of application and the confidence in the results we achieve. We could not ask for a better product backed by sound technical support.”
Saint-Gobain Weber’s specialist concrete repair products were selected to facilitate this major refurbishment. webercem spray DS, a ready-to-use, polymer-modified, cement-based concrete mix, with inert limestone aggregates and dust suppressants, is especially designed for dry process spray application to give high early strength, reduced rebound and maximum application thickness. Up to 150mm thickness can be applied in one pass on vertical or overhead faces without any additional mesh reinforcement. webercem spray DS complies with the Highways Agency Specification Class 29F for major structural repairs. The rapid strength development and dimensional stability of webercem spray DS, with an initial set in 2 – 3 hours, was especially valuable in the tidal conditions at Weymouth. webercem spray DS gives a compressive strength in seven days of 49.8MPa.
webercem spray RS ready-to-use, dry-sprayed concrete is able to achieve rapid repairs to structures within tidal zones, dock walls, jetties, seawalls and other coastal structures. It achieves a permanent repair where time constraints demand the earliest possible strength gain with reduced rebound and maximum applied thickness. It can be applied up to 100mm thickness in one pass to vertical faces.
“With skilled, specialist application together with the technical characteristics of webercem spray DS we were able to deliver the project on time and on budget. The client is delighted with the result and we hope this will ensure further work for us in Weymouth.”
Since 1980 the fort has slowly been restored with work undertaken through the Manpower Services Scheme, and other interested bodies and individuals, including the Weymouth Civic Society. It is now a successful and popular museum and tourist attraction. The structure has received a £1.8m lottery grant and a further investment of £600,000 from the local authority and English Heritage has been made. In 2012 Nothe Fort and Gardens was at the centre of the 2012 Olympic and Paralympic Games hosting the sailing events which attracted almost 5,000 ticketed spectators a day over the two week spectacular.