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Re: usg casting plaster

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  • gregsfoundry
    Hi John..I guess what you a looking at is an investment casting process around foam. I have used a mix of 1 part plaster to 2 parts sand ...some people use
    Message 1 of 10 , Apr 1, 2009
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      Hi John..I guess what you a looking at is an investment casting process around foam. I have used a mix of 1 part plaster to 2 parts sand ...some people use brickies loam ....It takes a lot to dry the mold...in a kiln at 700c for 24 hours and the mold is best made with a chicken wire bracing built into it. Anyway thats how I do it ...not prepared to risk volatiles and moisture when I pour the bronze. If you stack the kiln full then its more economical. Some of my bronzes have my fingerprints from the wax still readable. If you quench the bronze the mold disintergrates. In terms of the viscocity of the mix this will depend on the amount of water you put in ....something that you will probably instinctively get. The trick is to keep the sand mixed untill you actually pour as it tends to sink. Hope this is of help.
      Greg
    • Leon
      ... The trick is to keep the sand mixed untill you actually pour as it tends to sink. Hope this is of help. Have you tried a thixotropic additive? Gelatin,
      Message 2 of 10 , Apr 1, 2009
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        --- In hobbicast@yahoogroups.com, "gregsfoundry" <gregorybold@...> wrote:
        The trick is to keep the sand mixed untill you actually pour as it tends to sink. Hope this is of help.

        Have you tried a thixotropic additive? Gelatin, agar, Benoite and polyacryalamide (water gell as sold for gardening and frac fluids)are some that come to mind. The 'poly' would be hard to dry out but it should completely eliminate the sand fall out problem.
        =================
        Leon McAtee
      • gregsfoundry
        Thanks Leon ...what a great idea to suspend the sand in water crystals or similar...you know this is really a wonderful group of people to help each other like
        Message 3 of 10 , Apr 2, 2009
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          Thanks Leon ...what a great idea to suspend the sand in water crystals or similar...you know this is really a wonderful group of people to help each other like this.
          ..Greg
        • Jack
          MUCH simpler is to use drywall compound instead of plaster - no sand or gelatin needed (Joint Finishing Compound in Australia - get it from builders supply
          Message 4 of 10 , Apr 2, 2009
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            MUCH simpler is to use drywall compound instead of plaster - no sand or gelatin needed (Joint Finishing Compound in Australia - get it from builders supply stores).

            Just mix with some water to a thin custard consistency and dip or brush onto the foam. Allow to dry between coats if you want a thicker layer or to ensure no gaps. Unused portion can be returned to the bucket for next time as it doesn't SET hard - it DRIES hard. A small bucket will last almost half a lifetime!
            Jack





            --- In hobbicast@yahoogroups.com, "gregsfoundry" <gregorybold@...> wrote:
            >
            > Thanks Leon ...what a great idea to suspend the sand in water crystals or similar...you know this is really a wonderful group of people to help each other like this.
            > ..Greg
            >
          • kidharris
            Homedepot also sells several versions of fast set drywall mud in a powder form in bags that have fast dry times 5 - 45 min that seem to work pretty well
            Message 5 of 10 , Apr 3, 2009
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              Homedepot also sells several versions of fast set drywall mud in a powder form in bags that have fast dry times 5 - 45 min that seem to work pretty well although I have only done very small scale experiments in the 5 minute type. looks similar to plaster.

              I merely mixed it, poured it in a container, pushed some objects into it to make impressions, waited ten minutes to dry, and put an acetylene torch to it. It was thick walled and did not crack. I don't have a furnace now to do better tests. May crack with larger molds.

              --- In hobbicast@yahoogroups.com, "Jack" <jacktarr68@...> wrote:
              >
              > MUCH simpler is to use drywall compound instead of plaster - no sand or gelatin needed (Joint Finishing Compound in Australia - get it from builders supply stores).
              >
              > Just mix with some water to a thin custard consistency and dip or brush onto the foam. Allow to dry between coats if you want a thicker layer or to ensure no gaps. Unused portion can be returned to the bucket for next time as it doesn't SET hard - it DRIES hard. A small bucket will last almost half a lifetime!
              > Jack
              >
              >
              >
              >
              >
              > --- In hobbicast@yahoogroups.com, "gregsfoundry" <gregorybold@> wrote:
              > >
              > > Thanks Leon ...what a great idea to suspend the sand in water crystals or similar...you know this is really a wonderful group of people to help each other like this.
              > > ..Greg
              > >
              >
            • JohnW
              A mix of drywall texture compound and water seems to work very well for this fellow. http://www.buildyouridea.com/cnc/hblb/hblb_prototype/prototype_4.html His
              Message 6 of 10 , Apr 3, 2009
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                A mix of drywall texture compound and water seems to work very well for this fellow.
                http://www.buildyouridea.com/cnc/hblb/hblb_prototype/prototype_4.html

                His final castings would be pretty hard t beat.

                JohnW

                --- In hobbicast@yahoogroups.com, "kidharris" <kidharris@...> wrote:
                >
                > Homedepot also sells several versions of fast set drywall mud in a powder form in bags that have fast dry times 5 - 45 min that seem to work pretty well although I have only done very small scale experiments in the 5 minute type. looks similar to plaster.
                >
                > I merely mixed it, poured it in a container, pushed some objects into it to make impressions, waited ten minutes to dry, and put an acetylene torch to it. It was thick walled and did not crack. I don't have a furnace now to do better tests. May crack with larger molds.
                >
                > --- In hobbicast@yahoogroups.com, "Jack" <jacktarr68@> wrote:
                > >
                > > MUCH simpler is to use drywall compound instead of plaster - no sand or gelatin needed (Joint Finishing Compound in Australia - get it from builders supply stores).
                > >
                > > Just mix with some water to a thin custard consistency and dip or brush onto the foam. Allow to dry between coats if you want a thicker layer or to ensure no gaps. Unused portion can be returned to the bucket for next time as it doesn't SET hard - it DRIES hard. A small bucket will last almost half a lifetime!
                > > Jack
                > >
                > >
                > >
                > >
                > >
                > > --- In hobbicast@yahoogroups.com, "gregsfoundry" <gregorybold@> wrote:
                > > >
                > > > Thanks Leon ...what a great idea to suspend the sand in water crystals or similar...you know this is really a wonderful group of people to help each other like this.
                > > > ..Greg
                > > >
                > >
                >
              • Andrew Werby
                1a. Re: usg casting plaster Posted by: gregsfoundry gregorybold@yahoo.com.au gregsfoundry Date: Thu Apr 2, 2009 4:27 am ((PDT)) Thanks Leon ...what a great
                Message 7 of 10 , Apr 3, 2009
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                  1a. Re: usg casting plaster
                  Posted by: "gregsfoundry" gregorybold@... gregsfoundry
                  Date: Thu Apr 2, 2009 4:27 am ((PDT))

                  Thanks Leon ...what a great idea to suspend the sand in water crystals or similar...you know this is really a wonderful group of people to help each other like this.
                  ..Greg

                  [Water crystals? You mean ice? To me this sounds like a seriously bad idea, but maybe I'm missing something...]

                  Andrew Werby
                  www.computersculpture.com
                • gregsfoundry
                  ... Water crystals are a sort of gelatin that absorbs water and holds it...great for the garden in dry climates. So not as dangerous as adding something hot to
                  Message 8 of 10 , Apr 3, 2009
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                    > [Water crystals? You mean ice? To me this sounds like a seriously bad idea, but maybe I'm missing something...]

                    Water crystals are a sort of gelatin that absorbs water and holds it...great for the garden in dry climates. So not as dangerous as adding something hot to something cold and wet...just a way of suspending the sand until the plaster sets....then moisture cooked out in kiln.
                    Greg
                  • postello@msu.edu
                    He s talking about sodiun polyacrylate and related super soaker gels. They were developed for use in drilling fluids (like bentonite) and to hold water in
                    Message 9 of 10 , Apr 4, 2009
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                      He's talking about sodiun polyacrylate and related "super soaker"
                      gels. They were developed for use in drilling fluids (like bentonite)
                      and to hold water in place where you do drip irrigation. A major use
                      now is in disposable diapers. They hold water, and I'm not sure that
                      this would be a great idea. Wear safety equipment if tou try it. I
                      do know someone who did a "fire in ice" demonstration at an iron pour,
                      pouring s full 100 lb. plus ladle of molten iron into a hole in a
                      clear block of ice. It looks like a red lamp, with steam coming out
                      of the top. I don't know why this is possible.

                      >
                      >> [Water crystals? You mean ice? To me this sounds like a seriously
                      >> bad idea, but maybe I'm missing something...]
                      >
                      > Water crystals are a sort of gelatin that absorbs water and holds
                      > it...great for the garden in dry climates. So not as dangerous as
                      > adding something hot to something cold and wet...just a way of
                      > suspending the sand until the plaster sets....then moisture cooked
                      > out in kiln.
                      > Greg
                      >
                      >
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