An inorganic mortar system for a chemical fastening of an anchor in a mineral surface includes calcium sulfate, a component A, and a component B for initiating a curing process. Component A includes water, aluminous cement, at least one plasticizer, and at least one blocking agent selected from phosphoric acid, metaphosphoric acid, phosphorous acid, and a phosphonic acid. Component B includes an initiator, at least one retarder, at least one mineral filler, and water. Component A is also a curable composition.