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This heading covers certain preparations (e.g., for furnace linings) with a basis of such refractory materials as chamotte and dinas earths, crushed or ground corundum, powdered quartzites, chalk, calcined dolomite, with an added refractory binder (for example, sodium silicate, magnesium or zinc fluosilicates). Many of the products of this heading also contain non-refractory binders such as hydraulic binding agents.
The heading also covers refractory compositions with a basis of silica for the manufacture of dental or jewellery moulds by the lost wax process.
The heading further covers refractory concretes consisting of mixtures of heat‑resistant hydraulic cements (e.g., aluminous cements) and refractory aggregates, used for the foundation of furnaces, coke ovens, etc., or for patching furnace linings as well as the following :(a) Compositions known as refractory "plastics", which are products sold as a dampened mass often consisting of a refractory aggregate, clay and minor additives. (b) Ramming mixes, other than dolomite ramming mixes, which are similar in composition to the products mentioned in (a) above and which, when applied by hand‑held pneumatic rammers, form a dense coating or filling. (c) Gunning mixes, which are refractory aggregates mixed with hydraulic setting or other binders, applied to furnace linings, sometimes even when these are hot, by special guns which project the mix through a nozzle using compressed air. The heading does not cover : (a) Dolomite ramming mixes (heading 25.18). (b) Carbonaceous pastes of heading 38.01.
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