Low-density cement slurries for cementing subterranean wells are described that comprise alkali swellable polymers as thickening agents that provide slurry stability. The polymers are preferably added as liquid latex dispersions, and may also comprise a surfactant that is present at a concentration below its critical micelle concentration. Particular utility is observed when the solid-volume fraction (SVF) of the slurry is less than about 40 percent. Also described are a method for increasing the viscosity of a cement slurry and methods for cementing a subterranean well.