A method of expanding expandable polymeric microspheres including contacting an aqueous slurry including unexpanded, expandable polymeric microspheres with steam in-situ during manufacture of a cementitious composition or article, wherein the aqueous slurry optionally further includes an admixture therefor. A method of manufacturing a cementitious composition or article includes: (i) contacting an aqueous slurry of unexpanded, expandable polymeric microspheres with steam proximate to and/or during said manufacturing of the cementitious composition to create expanded polymeric microspheres; (ii) pre-wetting the expanded polymeric microspheres; and (iii) mixing the pre-wetted, expanded polymeric microspheres with cement and water to form the cementitious composition, wherein the aqueous slurry optionally further comprises an admixture therefor.