Abstract: The curing time of cementitious cellulose ether comprising-compositions can be controlled by incorporation into the composition i) a cationically-modified or a secondary or tertiary amino-modified cellulose ether or ii) a cellulose ether comprising a hydroxyethoxyl substituent alone or in combination with one or more other substituents bound to oxygen, wherein the ethylene oxide molar substitution MShydroxyethoxyl is either from 2.2 to 3.2 and the percentage of unsubstituted anhydroglucose units is up to 8.5 percent or the ethylene oxide molar substitution MShydroxyethoxyl is less than 2.2 and the percentage of unsubstituted anhydroglucose units is up to 12 percent.