Manufacture of refractory products

23.1 Manufacture of glass and glass products 23.2 Manufacture of refractory products 23.3 Manufacture of clay building materials 23.4 Manufacture of other porcelain and ceramic products 23.5 Manufacture of cement, lime and plaster 23.6 Manufacture of articles of concrete, cement and plaster 23.7 Cutting, shaping and finishing of stone 23.9 Manufacture of abrasive products and non-metallic mineral products n.e.c.