Re: [ATM] List "reference material"

["Stuart Hutchins" <stuart452@earthlink.net>]

----- Original Message ----- 
From: "Richard Schwartz" <richas@earthlink.net>

Subject: RE: [ATM] List "reference material"


> Use of the word "plaster" is to be discouraged.   The proper material is
> dental stone.   The problem with plaster is that it disintegrates when 
> wet.
> However, I have a plaster project in my list of things to do, wherein
> additives to plaster (such as white glue) would be evaluated in an attempt
> to strengthen and waterproof it.

Hmm, yes, to most people "plaster' means Plaster of Paris, which is refined 
gypsum, i.e. calcium sulfate.  But generically speaking, the proper word 
would be "gypsum cement", which seems to be improved plaster, since the MSDS 
says it is also calcium sulfate.  This includes the dental stones and the US 
Gypsum trade-names Hydrocal and Hydrostone.  Hydrostone is the most water 
resistant of the group, has 10,000 psi conpressive strength, and you can 
make your own imitation by adding 5% Portland Cement to Hydrocal.

Question:  Has anyone tried the white liquid concrete additives with plain 
old Plaster of Paris?

Stuart Hutchins 

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