Steenwolgranulaat rockwoolStonewool granulate is shredded basalt substrate. Substrate slabs are being used in greenhouse cultivation to grow e.g. tomatoes . Substrate slabs last for about one year and after that these are collected. After collection the slabs are treated: organic pollutants and foils are getting removed and the slabs is shredded to what we call stonewool granulate. The ceramic industry uses stonewool granulate as an alternative material.