The invention concerns a plate whereof the body comprises a binder containing Portland cement, a sulphoaluminous clinker and a calcium sulphate source: the binder comprises, by weight 30 to 80% of Portland cement, 20 to 70% of sulphoaluminous binder, 5 to 20% of a calcium sulphate source, and 0.4 to 7% of a water-reducing plasticizer or highly waterreducing superplasticizer admixture; it contains light aggregates in an amount such that the final density is close to 1, of the order of 0.8 to 1.5.