Process for the manufacture of plasterboards exhibiting a core density of less than 0.77 comprising the stages of the formation of a foam from water and a surfactant composed of at least one alkyl sulphate of formula H(CH.sub.2).sub.nOSO.sub.3.sup.-M.sup.+, in which n is a number between 6 and 16, M is a monovalent cation and the mean number of carbon atoms n.sub.m is from 9 to 10, and the introduction of the foam obtained into a plaster slurry, characterized in that the amount of surfactant introduced does not exceed 0.32 g/l of plaster slurry. Application to the manufacture of lightened plasterboards.