FIELD: manufacture of building materials, mainly, compositions of groove-crest slabs; applicable in manufacture of internal walls and partitions in buildings of various types. SUBSTANCE: mixture contains solution of magnesium chloride in form of bischofite solution with density of 1.3 d/cu. cm and cellulose additive in form of fiberized waste paper-cardboard material and additionally foaming agent in form of solution of saponified wood resin with density of 0.07 g/cu.cm and slaked lime with the following amounts of components, wt.%: magnesian binding agent 51-3-52.5; bishofite solution with density of 1.3 g/cu.cm 22.6-23.5; fiberized waste paper-cardboard material 2.0-2.35; saponified wood-resin solution with density of 1.07 g/cu.cm 2.25-2.35; slaked lime 0.3-0.35; the balance, water. EFFECT: reduced average density of groove-crest slabs with preserved preset strength. 1 tbl
