Ultracal additives

Terry Gallentine · Post by **Terry Gallentine** » Mon Sep 29, 2014 12:55 pm

What are the best sand or grog particle sizes to add to Ultracal plaster to get the most durable mold for firing to 1400F? Which is preferable, sand or grog?

Morganica · Post by **Morganica** » Mon Sep 29, 2014 3:02 pm

For me? Neither. I prefer fiber chop, or fiber fabric. But what else are you using with the Ultracal?

Terry Gallentine · Post by **Terry Gallentine** » Mon Sep 29, 2014 3:15 pm

In the past, I have been mixing silica sand (#4030) with standard moulding plaster. It gives me a mold that lasts for five or six firings and for most jobs that is fine. For a current job, I would like to increase the durability of the mold. The Ultracal when mixed the same way, maintains a good surface hardness but has a tendency to crack. Many years ago I experimented with fiber but I didn't get satisfactory results so I went with standard silica.

Terry Gallentine · Post by **Terry Gallentine** » Fri Oct 03, 2014 1:21 pm

Morganica,
I have decided to try out fiber as an additive as you suggested but I have some questions. I assume that you are referring to chopped ceramic fiber not chopped glass fiber (as used in cement), am I correct? What fiber length are you using? My molds vary quite a bit in thickness so I am also considering using Hydroperm. Have you ever used Hydroperm with chopped fiber?
Thanks for your expertise.

WarmGlass.com

Ultracal additives

Ultracal additives

Re: Ultracal additives

Re: Ultracal additives

Re: Ultracal additives