19 Stone, rock, clay and minerals; pitch, tar, bitumen and asphalt; spackling compound; building and construction materials and elements, not of metal; refractory construction materials, not of metal; concrete; cement coatings; stones; mixtures for admixture to building materials, not of metal; mixtures for admixture to concrete, cement coatings and stone; liquid mixtures for admixture to building materials, not of metal; liquid mixtures for admixture to concrete, cement coatings and stone; furnace linings of non-metallic materials; ceramic compounds (term considered too vague by the International Bureau - Rule 13 (2) (b) of the Regulations); ceramic compounds for lining metallurgical furnaces; prefabricated building components (non-metallic -); sand