Re: [ATM] Source for Dental Stone

[mdholm@telerama.com]

>Try calling a few commercial building supply outlets in your area and
>ask for Hydrocal, Ultracal, Hydro-stone or gypsum cements.

Properties for Hydrocal and Hydrostone are available at the US Gypsum web site.
 Hydrostone is the one that sounds best to me because it appears to have the
best resistance to water after curing, the lowest expansion/shrink during
curing, and the highest strength.  There is also Tuff-Stone which appears to be
Hydrostone with some sort of strengthening fibers added.  Probably raises the
tensile and impact strengths of Hydrostone.  The compressive strength is pretty
good without the fibers.

One thing to keep in mind about all these gypsum cement products is that they
probably absorb water vapor out of the air (and maybe carbon dioxide too?)
making them loose the ability to react to a strong solid over time.  This would
affect the unreacted dry powder, not the cured solid.  Probably need to store it
in a well sealed watertight package for long term storage.  Carbon dioxide will
go through plastic that water will not.  It can be slowed down with a thicker
layer of plastic.

Among the dental plaster products, the ones with "stone" in the name or
description appear to be stronger and more water resistant than plain dental
plaster.  There are a lot of brand names, and I don't have them all sorted out.
 They come in different colors, presumably to indicate the different products,
but the color code does not appear to be standardized between manufacturers.

Mark Holm
mdholm@telerama.com
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