| 摘要 |
1481788 Gypsum BPB INDUSTRIES Ltd 8 Oct 1974 [25 Oct 1973] 49749/73 Heading C1A [Also in Division E1] The tendency of gypsum articles to sag in damp conditions is reduced by incorporating gallic acid (preferably in a proportion of 0À01 to 0À04 wt. per cent of the gypsum, calculated as calcium sulphate hemihydrate). The gallic acid may be added to the gypsum plaster, or gypsum and gallic acid may be mixed and then calcined to form a plaster; in either case, the plaster is then mixed with water and the articles are shaped in conventional manner. |
