The quick lime powder containing gypsum has a hardening property in mixing with water. However, the quick lime sets too quickly and has much exothermic property, depending on the hydraration. In this report, it was found that heat of the lime goes down in mixing with slaked lime or slaked dolomite, and the hydration of quick lime is retarded by adding a small amount of calcium gluconate.
Plasters were prepared from the mixtures in various proportions of quick lime, gypsum, slaked lime or slaked dolomite and calcium gluconate. Physical properties of the plasters such as expansion or shirinkage, heat evolution, setting time, strength and soundness etc were measured.
Results are summerized as follows :
(1) The best test results were obtained from the mixtures of quick lime 30-40 parts, slaked lime or slaked dolomite 70-60 parts, gypsum 2-4 parts and calcium gluconate 0. 25-0. 50 parts.
(2) The temperature of the plasters goes up 10-30°C in the setting and hardening stages.
(3) The setting time of the plasters are easily controlled by changing the amount of gypsum and calcium gluconate.
(4) The strength of the test pieces from the plasters is increased time by time, for example, 30-70 kg/cm² in bending strength and 40-120 kg/cm² in compressive strength after 28 deys.
(5) The test pieces are sound in steam test.
(6) The strength, hardness, water retension property and viscosity of the plasters mixed slaked dolomite are higher than them of the plasters mixed slaked lime.
(7) Much retarder should be spent in the use of slaked dolomite than in the use of slaked lime as mixing materials.

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