This report presents the results of research to give the Thaumasite Expert Group data on which to establish interim recommendations for concrete mixes designed to minimise deterioration due to the thaumasite form of sulfate attack. Earlier site and lab investigations carried out by BRE on the problems of sulfate attack showed that the mineral thaumasite is responsible for the deterioration of concrete and mortars specifically designed to give good sulfate resistance. At that time there were indications that the use of blast furnace slag cement could improve the resistance of limestone aggregate concretes.