Mix plasters by weight not volume, each plaster has it unique USE number.
How to mix Plaster:
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 10 lb. of plaster requires 7 lb. of water. First weigh out the plaster you need, take that amount and multiply it by .7,(point 7), (7/10) 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.
Also called condensation-cure silicone, these are high-tear silicone rubbers that are known as the “work horse” of the industry because of their performance and economy. Tin cured silicone molds are used for casting wax, gypsum, polymer modified gypsum, etc. but are best known for standing up to production casting of urethane, epoxy and polyester resins. They are also good for casting low temperature melt metal alloys.
Silicone Rubber - Platinum Cure
Also known as addition-cure silicone, platinums exhibit the lowest long-term shrinkage and have the longest library life of all mold rubbers (with a price tag to match). While good for making molds for casting a variety of materials, platinums also have application and physical properties that other rubbers do not. As a result, they are used for other applications. For example, some are certified “skin safe” and can be applied directly to human skin. They are also used for making prosthetic and orthotic devices, skin safe appliances and effects, etc. Some are certified “food safe” for culinary applications.
Easy to use and exhibiting good wear resistance they can be poured, brushed on or sprayed onto prepared surfaces and cure with negligible shrinkage. They are economical, reproduce exceptional detail and are best suited for production casting of concrete, gypsum and wax.
Urethanes are very adhesive read the instructions to find out the correct release agent.
Urethanes hate water, make sure everything is dry.