Abstract
Two kinds of dolomite plaster, which were produced by calcining dolomite (Kuzuu, Tochigi Pref.) at about (a)900°C or (b) 700°C and grinding after hydration, by proper amount of water, were observed to be of inferior quality of small hardening strength and easily cracking.
these samples of dolomite plaster were tested by adding small amount of gypsum plaster (or calcined gypsum, Ca SO4.1/2H2O), which was obtained by calcining crystal gypsum (CaSO4.2H2O) from salt making plants. These samples of mixed dolomite-gypsum plaster (dolomite plaster (a) or (b) 95-75 parts to gypsum plaster 5-25 parts) were tested on their hardening compressive strength (7 days curing) and the cracks in the plaster layer on wrought iron plate (7 days in air or in 110°C hot aix curing). The addition of calcined gypsum (10-15%) to both (a) & (b) kinds of dolomite plaster makes remarkably good effect to increase the hardened compressive strength and to decrease or exclude the cracks in the hardened layer of mixed plaster of calcined gypsum and dolomite plaster.
