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Old 12-17-2014, 01:16 AM
Art-Deco Art-Deco is offline
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Join Date: Jan 2012
Location: usa
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Re: Sculpting with cement

Quote:
Originally Posted by Andrew Werby View Post
I didn't know Hydrocal or Hydrostone contained Portland cement; if they do it can't be very much, since they act a lot more like plaster than concrete.

I meant hydrostone, ultrastone and duracal have Portland, not hydrocal, it even says "Warning: contains Portland cement" on the bags, the exact ingredients are in the MSDS:


HYDROSTONE

Plaster of Paris, & Portland Cement

Plaster of Paris >90%
Portland Cement <5%
Crystalline Silica <5%

http://shop.clay-planet.com/MSDS/pla...%20Plaster.pdf


Ultracal 30

Plaster of Paris >85%
Portland Cement <10%
Crystalline Silica <5%

Ultimately it appears the difference between those two are Ultracal has a little more Portland added to it, and they have less than 5% and 10% Portland respectively, so in a 100# bag the hydrostone has a little under 5# of Portland, Ultracal a little under 10#. It also looks like you can take Plaster of Paris and add up to 10% Portland to it at home, more than that and I guess it acts more like concrete- taking hours to set up and days to fully cure.
Ive used hydrostone and ultracal, they stay syrupy liquid and then suddenly and rapidly harden up, very unsuitable for hollowing out a large cast since they have almost no plastic stage where you can work and mold it.
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