The Cement Plant Operations Handbook. Cement milling 110 111 The Cement Plant Operations Handbook – Seventh Edition 6. Cement milling Finish milling is the grinding together of clinker with some 3-5 per cent gypsum, natural or synthetic, for set control, and quite often other components: blastfurnace slag, pozzolan, silica fume, limestone or pulverised fuel ash ('pfa'