Self foaming cellular glass–ceramics were obtained by sintering mixtures of a basalt scoria and soda lime cullet for 15min at 1050 and 1100°C. The effect of polyvalent ions (Fe3+/Fe2+) on porosity (from 53 to 86vol.%) and crystallization was studied for different mixtures subjected to different thermal treatments. Due to the range of mechanical strength values (crushing strength from 2 to 50MPa) and total porosity achieved, these porous glass–ceramics could be applied as building materials, as lightweight aggregate for concrete or as lightweight panels. •We produced glass–ceramic foams from cheap and waste raw materials.•A soda lime cullet and basalt mixture foaming mechanism was investigated.•The polyvalent ions role (Fe3+/Fe2+) on generating the porosity was described.•Microstructure and mechanical strength of the glass–ceramic foams were studied.•A potential application in the building industry is discussed.