plaster for casting

[Chris Lowry]

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]

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

Dana W.

[Chris Lowry]

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

[heywilli]

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]

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]

Make sure you get pottery plaster Number 1.

Its much stronger than regular plaster

[FusedLightStudio]

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

[JestersBaubles]

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]

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]

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

[FusedLightStudio]

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]

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