Date: Thu, 25 Sep 2003 13:15:07 -0400
Subject: Re: PUPT: Ultracal vs. Plaster
From: robert smythe <robertsmythe-AT-mumpuppet.org>


Ultracal (tradename) contains cement and used to make stamping dies. It 
is intentionally hard and durable, and is fairly non-porous.

Hydrocal is a general purpose, fine textured gypsum plaster that works 
well for neoprene molds.

#1 pottery plaster is an absorbent plaster made specifically for 
creating slip casting molds, where wall thickness is achieved through 
the absorption of liquid through the plaster. Since it likes moisture 
so much, it can actually set up if the powder is exposed to damp air 
(resulting in gritty mixtures and rough feeling plaster.

Remember, too, when making multiple castings, that the time spent with 
liquid in the mold will change depending on how dry the mold is.

I'd recommend:
1) #1 pottery plaster (thoroughly dried. When wet (from a previous 
pour) it still does work pretty well)
2) hydrocal
3)plaster of paris

Never ultracal.

Robert


On Thursday, September 25, 2003, at 12:57 PM, Ken Berman wrote:

> If technical questions offend you, please delete this message now.
>
>
>
> The Question: Can anyone out there offer a definitive answer to 
> confirm my suspicion that Ultracal is a terrible mold medium for 
> neoprene casting.  I want to know for sure that plaster is a better 
> medium,  because it seems to be much more porous and absorbs much more 
> moisture from the neoprene.  I used to use plaster, but have been 
> informed that ultracal is better (?) Everytime I have used ultracal 
> however, I have waited atleast three days for the neoprene to set in 
> the mold in order to be ready to get pulled, and sometimes still 
> without successful results. With plaster I usually wait only 8 hours.  
> Chicago Latex (the manufacturer of neoprene) can not supply an answer. 
>  Maybe someone here who uses neoprene can help me form a conclusion so 
> I can get rid of the delusion that I should listen to the advice.
>
>
>
> The Problem: Presently, I am making some neoprene heads using Ultracal 
> molds (persisting with the advice I was given).  I poured the rigid 
> neoprene  on Tuesday at 2pm and three days later, the neoprene is 
> still white inside, rather than the beige color that indicates it is 
> ready to be pulled from the mold.  As a risky test, I pulled one of 
> the neoprene casts, and sure enough, it was not ready and it stretched 
> and deformed.  Now I have to redo that particular pour, and I am still 
> waiting for the others to set (perhaps another three more days!?-AT-#)
>
>
>
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Robert Smythe
Artistic Director
Mum Puppettheatre
115 Arch Street
Philadelphia, PA 19106
T: 215.925.7686
F: 215.922.5184

robertsmythe-AT-mumpuppet.org
http://www.mumpuppet.org


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