23.20 — Manufacture of Refractory Products

This class includes: - manufacture of intermediate products from mined or quarried non-metallic minerals (e.g. gravel, stone or clay) - manufacture of refractory mortars, concretes, etc. - manufacture of refractory ceramic goods, e.g.: • heat-insulating ceramic goods of siliceous fossil meals • refractory bricks, blocks and tiles, etc. • retorts, crucibles, muffles, nozzles, tubes, pipes, etc.

This class also includes: - manufacture of refractory articles containing magnesium oxide, calcium magnesium oxide or chromite