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Old 07-13-2019, 08:12 PM
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Franklin Sankar Franklin Sankar is offline
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Type of plaster

Is #1 pottery plaster the same as dental plaster? I have no pottery plaster.
Franklin
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Old 07-13-2019, 09:18 PM
Steven O'Day Steven O'Day is offline
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No. #1 pottery plaster is straight plaster, dental plaster is a mix of plaster and refractory and maybe other stuff. Each brand has it's own mix so it is difficult to compare them. If you are using this for glass casting you will need to adjust the amount of silica in the mix or maybe just use the dental plaster by itself. The amount of water and mixing technique is important.
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Old 07-13-2019, 09:24 PM
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Thanks for the reply. When you say straight plaster do you mean plaster of paris?
I can get dental plaster.
Franklin
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Old 07-13-2019, 09:58 PM
Steven O'Day Steven O'Day is offline
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Plaster of Paris is a little different but close, they are both forms of calcium sulfate. There are lots of different plasters and you will need to test the ones you have for what you are doing. Also, I mis-poke about dental plaster, some do not have refractories in them.
Probably the reason pottery plaster started to be used for glass casting is that it is readily available in school studios, not necessarily because it is the best plaster to use. Sometimes the water ratio and mixing is more important than the type of plaster. Consistent testing is important.
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Old 07-13-2019, 10:28 PM
Steven O'Day Steven O'Day is offline
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Also, dental plaster investment is often just called dental plaster. Dental plaster is similar to pottery #1 or plaster of Paris, investment is similar to casting mold mix.
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Old 07-14-2019, 11:19 AM
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Yes I just discovered there are plaster and there are plaster. Getting the relevant info in the specs. Helps.
Franklin
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Old 07-14-2019, 11:54 AM
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we mix regular plaster with 95 percent alumina castables Franklin. It's nice.
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Old 07-16-2019, 05:52 AM
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That sounds like a good use for expired refractory cement. If expired don’t work fresh still is a winner.
Thanks for confirming it’s possible Pete. So it replaces the silica flour.
Franklin
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Old 07-16-2019, 08:08 AM
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Pete VanderLaan Pete VanderLaan is offline
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It is more refractory than the plaster certainly. It doesn't expand a ton and that's handy. Plaster tends to turn punky when repeat firings are done with it but I think the primary function of the silica is keeping the mold from cracking. Refractory castable does that. I'm not so sure about expired cement.

Missouri Refractory sells calcium aluminate if you ask after it. They never advertise the stuff but it's the cement that makes castables bind and set. I do get 25 lb bags of it and seal it up in airtight containers. Then, when a castable has gone by, I add some. Too much and the peak temperatures for the castable will be compromised.
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Old 07-16-2019, 10:08 AM
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Franklin Sankar Franklin Sankar is offline
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Nice how you add the refractory. I am going to try with some green cast 95. Kind of old but itís free. I am most curious to see the outcome. Refractory needs little water but plaster need much more water. That is going to be interesting to see how they work together.
Thanks
Franklin
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