plaster for casting - WarmGlass.com

plaster for casting

Use this forum for discussion on kiln casting, pate de verre, and related topics.

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Chris Lowry
Posts: 49
Joined: Thu Sep 24, 2015 12:35 pm

plaster for casting

Postby Chris Lowry » Tue Oct 03, 2017 5:14 pm

Sorry for the stupid question but I can't really find what I'm looking for with the search function.

What type of plaster do you use to cast with? I know there are products from R&R but I'm just wondering about plaster silica type molds.

What I understand is dental plaster is good but I also read somewhere that Hydrostone plaster is the same. Is that true?

I've also heard that casting plaster is good... is that the same as 20 minute casting plaster?

Thanks for any help that might be out there.

JestersBaubles
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Joined: Fri Feb 25, 2011 12:01 am
Location: North Logan, UT
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Re: plaster for casting

Postby JestersBaubles » Fri Oct 13, 2017 10:39 pm

50/50 mixture of pottery plaster and silica. Both can be purchased cheaply from any pottery supply.

Dana W.

Chris Lowry
Posts: 49
Joined: Thu Sep 24, 2015 12:35 pm

Re: plaster for casting

Postby Chris Lowry » Sat Oct 14, 2017 12:08 am

Thanks... that's what I ordered but it will be awhile before I get to try it.

heywilli
Posts: 4
Joined: Tue Jul 16, 2013 9:10 pm

Re: plaster for casting

Postby heywilli » Tue Nov 28, 2017 8:38 pm

Hi I typically use Hydrocal and silica flour 1:1 for the first layer if hand building and then add an equal amount of silica sand to the silica flour or hydrocal. I find that this makes pretty strong molds that divest quiet easily. If I am making a larger mold and I worry about mold cracking, for hand built molds I will first make several layers of plaster and then dip drywall tape pieces into the wet plaster mix and apply this around the mold and then cover with another layer of plaster for a total of about 4 layers of plaster. If you cannot find Hydrocal then pottery plaster works fine as well. This is much more economical that using the R & R mix and I find I get clean castings with this mixture which are easily divested. Hope this helps.

Don Burt
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Re: plaster for casting

Postby Don Burt » Wed Nov 29, 2017 1:08 pm

heywilli wrote:Hi I typically use Hydrocal and silica flour 1:1 for the first layer if hand building and then add an equal amount of silica sand to the silica flour or hydrocal. I find that this makes pretty strong molds that divest quiet easily. If I am making a larger mold and I worry about mold cracking, for hand built molds I will first make several layers of plaster and then dip drywall tape pieces into the wet plaster mix and apply this around the mold and then cover with another layer of plaster for a total of about 4 layers of plaster. If you cannot find Hydrocal then pottery plaster works fine as well. This is much more economical that using the R & R mix and I find I get clean castings with this mixture which are easily divested. Hope this helps.


You put plaster molds with drywall tape in them into a kiln? Nothing bad happens? Smoke issues?

Peter Angel
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Joined: Fri Oct 31, 2008 9:26 am
Location: Newtown, Sydney, Australia.

Re: plaster for casting

Postby Peter Angel » Thu Nov 30, 2017 2:25 am

Make sure you get pottery plaster Number 1.

Its much stronger than regular plaster
Peter Angel
http://peterangelart.blogspot.com/

A bigger kiln, A bigger kiln, my kingdom for a bigger kiln.

FusedLightStudio
Posts: 28
Joined: Wed Jan 24, 2018 1:33 pm
Location: Georgia

Re: plaster for casting

Postby FusedLightStudio » Sat Jul 07, 2018 9:44 am

Could I use just cleaned/sifted beach sand in the second layer?
If not - wondering where to get grogg...

JestersBaubles
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Location: North Logan, UT
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Re: plaster for casting

Postby JestersBaubles » Sun Jul 08, 2018 10:16 am

FusedLightStudio wrote:Could I use just cleaned/sifted beach sand in the second layer?
If not - wondering where to get grogg...


Any place that carries pottery supplies should have grog, silica flour, and pottery plaster.

Dana W.

FusedLightStudio
Posts: 28
Joined: Wed Jan 24, 2018 1:33 pm
Location: Georgia

Re: plaster for casting

Postby FusedLightStudio » Sun Jul 08, 2018 12:50 pm

JestersBaubles wrote:
FusedLightStudio wrote:Could I use just cleaned/sifted beach sand in the second layer?
If not - wondering where to get grogg...


Any place that carries pottery supplies should have grog, silica flour, and pottery plaster.

Dana W.


If only I did not live in a rural area ... I've gotten so lazy with being able to shop for everything online, driving an hour to a pottery store seems like a huge burden !

But what do you think about using sand as grog?

Kevin Midgley
Posts: 608
Joined: Mon Mar 10, 2003 11:36 am
Location: Tofino, British Columbia, Canada

Re: plaster for casting

Postby Kevin Midgley » Sun Jul 08, 2018 2:50 pm

You don't know what is in the beach sand and if it will harm your glass or your kiln.

FusedLightStudio
Posts: 28
Joined: Wed Jan 24, 2018 1:33 pm
Location: Georgia

Re: plaster for casting

Postby FusedLightStudio » Sun Jul 08, 2018 10:28 pm

You’re right of course, Kevin. I should have said, this is sand that was brought in to augment a beach (so, artificially clean). I sifted it, and also I have used it in the kiln under plaster molds, and it fires fine.

I did use it today as grog in second layer of a mold, which is now drying in the toaster oven, and will fire it with glass tomorrow. Will see how it goes and report back.

FusedLightStudio
Posts: 28
Joined: Wed Jan 24, 2018 1:33 pm
Location: Georgia

Re: plaster for casting

Postby FusedLightStudio » Thu Jul 26, 2018 8:39 pm

A belated report back - the sand worked. The mold held together very well and the cast turned out fine.


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