Edwards Diving Services Ltd were appointed to undertake repairs to an effluent sump tank at a large steelworks site in South Wales. The tank contains both sulphuric acid and caustic soda when it is operational. The concrete soffit of the tank had suffered severe damage in areas where the acid had come in to prolonged contact with it. EDS broke out the defective concrete areas, installed new reinforcing mesh tied back in to the good concrete and repaired the areas using Natcem 35 repair mortar. Works within the tank were limited to a narrow working window due to the time taken to purge the tank of all acid and caustic soda residues prior to entering and the plant needing to be operational again. As a result, the fast setting time and high early strength of the Natcem 35 repair mortar was the ideal solution, enabling a number of layers of application within the available working window. The repairs were ultimately completed ahead of time and to the satisfaction of the customer.