1. Always weigh out the amount of plaster you need, then look up the water by weight percentage. For example USG #1 Pottery for making molds uses 70% water to plaster. So 5 lb. of plaster requires 3.5 lb. of water. First weigh out the plaster you need, take that amount and multiply it by .7, (point seven, 70%) this gives you how much water to use.
2. Generally speaking the larger the percentage of water the softer and more absorbent the plaster will be. The harder the plaster the less water used.
3. Hot water will speed up the set time and cold water will slow it down.
4. Place the water in a suitable sized container. Always add plaster to water. Pour the plaster into the water and let slake for one minute. Mix by hand or with a Jiffy Mixer, being careful not to suck air into the plaster. When the mixture is lump free it is ready to pour; don’t wait for it to start to thicken. It should look like whole milk when you pour the plaster.
WARNING: This product can expose you to chemicals including Silica, crystalline (airborne particles of respirable size), which are known to the State of California to cause cancer. For more information go to www.P65Warnings.ca.gov.