All gypsum cements and plasters expand upon setting, but this one expands the least. So if it's pattern making you're into, this is probably the product to use. A very pale grey color, Ultracal 30 seems to be the material of choice for latex and latex foam casting. A hard material when cast, and is somewhat difficult to tool upon removal from the mold, but will yield to any of the commonly used riffler files and the like.
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