The invention relates to a method of making a particulate material comprising; providing mineral wool base material in a form having size at least 80% not more than 40 mm, subjecting the mineral wool base material to sintering by use of a pulse combustor and thereby forming a particulate material in the form of particles having size at least 80% not more than 20 mm. An apparatus for carrying out the method comprises means for size reduction of coherent mineral wool substrate and a reaction chamber in communication with a pulse combustor.