A method of retarding the setting time of cement

摘要

The setting time of a cement which sets on hydration with water, such as Portland cement, is retarded by adding thereto a mixture of one or more water-soluble silicofluorides with one or more inorganic or organic acids dissociable in water (provided that the silicofluoride and the acid are not both H2SiF6). The silicofluoride may be H2SiF6 or Mg, Zn, Pb, Al or ammonium silicofluoride, and the acid may be phosphoric, boric, acetic, or succinic. The mixture may be added to the water used for mixing the cement. The cement may be mixed with blast furnace slag, siliceous material, or pozzolanic material to form mortar or cement.