Oxford Street, London, UK

THE PROJECT

The basement vaults and corridors at 120 Oxford Street run under part of the building and extend under the pavement area. In 2020, after an engineering report highlighted a failed previous waterproofing system and failed existing repairs, corrosion of steel “H” section and reinforcement as well as breaking up of the basement floor, it was clear a complete refurbishment was needed to protect against further water ingress. There were large areas of defective concrete to the ring beams and columns - mainly due to water ingress from above, failure of previous waterproofing and repairs, and the floor was breaking up due to failed old repairs and general wear of the area. This had led to potholes in the floor and loss of concrete, which was not only a health and safety issue but would eventually result in the potholes enlarging and increased deterioration of the floor surface. By November 2020 parts of the basement were under 3ft of water.

THE SOLUTION

Fosroc completed a visual inspection of the site for the project specification document. A more detailed examination of the condition of the substrate and structure was then undertaken following a preparatory phase of work by contractor City Remedial. Firstly, Nitobond EP was used onto glazed tiles as the primer. Nitocote CM210 cementitious coating – which is capable of resisting up to 3 Bar (30m) negative water pressure - was then applied to the prepared brickwork surfaces to prevent further water ingress. Given the confined spaced nature of a basement walkway, the standard dry spray method would have generated too much dust, so Renderoc HB45, which is typically a hand-applied repair mortar, was spray applied at a thickness of between 10mm – 20mm.

THE BENEFITS

The wet spray method generates minimal rebound, excellent yield and minimal dust, making it suitable for confined / limited site working spaces. QC practices are also more straightforward as bagged material is mixed prior to entering the machine, rather than at the nozzle - as is the case with the dry spray method. This method also negates the possibility of any voids as the mortar is better compacted, than when applied by hand. It also provides a higher bond performance and can be applied much faster, while maintaining the same high quality finish as a hand-applied application.