The tank had been exhibiting signs of corrosion in the top 500 mm of the internal wall and along the top of the wall, due to prolonged exposure to the various chemicals and gases associated with sewerage. It was determined that the solution required would need to be able to resist HS2 and sulphate attacks, whilst improving the durability of the concrete and extending the service life of the structure in this aggressive environment.

NCS installed specialist concrete performance coatings to provide protection from the microbial induced corrosion. It was determined by the NCS team that a specialist mortar combined with an antimicrobial technology with crystalline technology had the ability to permanently block pores, capillaries and microcracks; delivering an impermeable integrated repair system that cannot be punctured, damaged or lose adhesion.

Survey results for the top of the Prefermenter Tank showed the amount of product that would be required to bring everything up to the highest point. In some areas it was up to 60 mm. Tolerances around the perimeter were a challenge with the limit of the tank at around 10 mm in a 3 m length. Overall the tolerances across the tank were ±5 mm to prevent twisting as a roof was to be installed prior to completion.