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Does Plaster of Paris shrink? Answered

Does Plaster of Paris shrink as it dries? I would like to make a mask out of it but I don't wan't it to shrink and crack.
Gratias agimus tibi,
josh1324

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Burf
Burf

Best Answer 9 years ago

No, it doesn't shrink. That's why it is used for things like paster cast impressions by police departments, and molds for casting gold and silver jewelry, etc.

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steveastrouk
steveastrouk

Answer 9 years ago

Well, it does shrink a bit - try doing thick sections.

Steve

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Burf
Burf

Answer 9 years ago

Its been a long time since I studied this, but as I recall, basic plaster of paris, without additives, actually expands slightly as it is curing. In the neighborhood of 0.3% to 0.5 %, nominal, if memory is correct. I don't recall the figures, but thermal expansion and contraction is also relatively small.

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steveastrouk
steveastrouk

Answer 9 years ago

True, buts it shrinks very slightly in storage, so that dental impressions can be problematic

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rickharris
rickharris

9 years ago

It will do what you want - DO NOT totally encapsulate any body past in Plaster of Paris.

you may find making a mould with alginate works better than a direct plaster cast,

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rachymarie
rachymarie

Reply 1 year ago

I have heard the horror stories - appendages lost and burning thermonuclear reaction when setting, and sets fast, hard as concrete, next to impossible to get it off or your limbs out of it - plaster of Paris doesn't muck around when it comes to messing you up

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rojo.balloon
rojo.balloon

9 years ago

Plaster will not shrink as it dries, therefore, it can be used to create a court-admissible cast as well as a reference which can be used in an investigation.