WarmGlass.com

Hello, Can I use OLD plaster which I did store in a plastic jar with lid, for casting ..... plaster, silica flour and chamotte. Jan

If it is still in a powder form, there is absolutely no reason not to use it.
It is an inorganic compound so there is no expiration date.
The other Jim

Thank you Jim. But I did read on Internet that Plaster can be used for about 4 month, so therefore my question. Jan

If it is on the internet, it must be so :>)
The other Jim

I've read that, too, a few times. Is it a myth put about by the manufacturers? Or is there more to it?

Here's some chat about it:
http://www.potters.org/subject82013.htm

I've got some that must be ten years old. I was thinking of putting it in the kiln before I tried to use it. Would I be wasting my time ? It's cheap enough to replace, I just don't like waste.

Jen

Look at the very top of the bag of plaster and see if there are small hard balls of plaster.

These balls are plaster that has already hardened.

Sift them out. The rest of the plaster is fine.

Pete