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Directions for Use For best results always maintain a fresh supply of CERAMI-CAL Gypsum Cement in stock that will be used within at least 90 days. Reason: strength, ability to purge, and setting time are affected by age. Strength, hardness, density and ability to purge depend upon the techniques employed when using CERAMI-CAL Gypsum Cement. These techniques are consistency (water-to-plaster ratio), temperature of mixture, mixing, pouring and parting. Always weigh both CERAMI-CAL Gypsum Cement and water to obtain proper consistency. With CERAMI-CAL Gypsum Cement best results are obtained for standard RAM working dies when a 40-consistency mixture is used (40 lb. water to 100 lb. gypsum cement). Less water than this increases the strength and hardness of the working die, but decreases permeability. More water gives a somewhat weaker and more permeable die or mold. It is undesirable to use less than a 30 consistency with CERAMI-CAL Gypsum Cement. Mixing time is related to the temperature of the slurry. This is determined by the temperature of the water and CERAMI-CAL Gypsum Cement. The lower the temperature,the longer the mixing time required and, to a moderate degree, the greater the strength. Extremely cold water should not be used. Water temperature should be maintained consistent at average room temperature of about 70°F. CERAMI-CAL Gypsum Cement should be sifted or strewn evenly, not dropped into the water. Allow to soak undisturbed for 2 to 5 min., then mix mechanically with a high-speed (1,750 rpm) propeller-type mixer for about 10 minutes. Mixing time can be standardized by controlling consistency and temperature. Pour slurry over the model or into the mold within two or three minutes after mixing, employing the same techniques used with most other plasters or gypsum cements. Case molds or models for use with the RAM process are generally made of HYDROCAL B-11 or ULTRACALŪ 30 Gypsum Cements. Molds or models may be made of plaster, rubber, wood, clay or any other material not affected by moderate increases in temperature which occur during setting of CERAMI-CAL Gypsum Cement. The technique used in parting the CERAMI-CAL Gypsum Cement working die is identical with those used for any other gypsum cement. In most cases, English Crown Soap, or its equal, is used when parting CERAMI-CAL Gypsum Cement from a gypsum cement model. CERAMI-CAL Gypsum Cement hardens and heats rapidly after the initial set. To determine when to begin the purging process, a temperature-difference method is recommended. When the die is poured, set aside a cup of slurry and note its temperature with a bimetal thermometer (its stem coated with grease) or a thermocouple. When the temperature reaches 23°F from the initial value, begin the purge cycle. Physical Properties - CERAMI-CAL Gypsum Cement Recommended Use Consistency ....................36-40
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