| abstract |
A dry, pulverulent coating compsn. is produced by calcining gypsum obtd. during desulphurisation of smoke gas, into hemi-hydrate, compacting or stacking the obtd. beta-hemi- hydrate and regrinding it to the following mesh size:- 0-0.3 m 30-40 wt.%; 0.03-0.06 mm 5-12 wt.%; 0.06-0.1 mm 10-20 wt.%, 0.1-0.2mm 9-15 wt.%; 0.2-0.5 mm 8-18 wt.% and 0.5-1.0 mm 7-15 wt.%. The prod. is then mixed with other components of the coating compsn. Also claimed is prepn. of CaSO4. hemihydrate by calcining gypsum contg. less than 10 wt.% moisture to form the beta- hemi-hydrate, compacting dry and at room temp. the finely divided prod. with briquettes which are then ground to the above particle size distribution. The prod. is used in the building industry to form, when mixed with water, smooth and fine surfaces. It has good rheological and setting properties. |