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Re: [hobbicast] Re: Need advice

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  • David Hair
    I ve been reading the last few post about POP molds. HELP, what is POP. I guess you can tell I m green at this. DH ... From: tmoranwms
    Message 1 of 24 , Apr 10, 2013
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      I've been reading the last few post about POP molds.
      HELP, what is POP. I guess you can tell I'm green at this.

      DH
      ----- Original Message -----
      From: "tmoranwms" <tmoranwms@...>
      To: <hobbicast@yahoogroups.com>
      Sent: Wednesday, April 10, 2013 2:16 AM
      Subject: [hobbicast] Re: Need advice


      > PoP dries out in three stages:
      > 1. Absorbed moisture. This is mostly driven off at any temperature with
      > low humidity (with the dry air around here in winter, it would be enough
      > to leave a mold sitting out for a few weeks to fully dry!), or over 212F
      > at any humidity.
      > 2. First chemical dehydration: when PoP sets, it forms a chemical
      > dihydrate (it's the hydrating process that makes it set, which is also
      > true of Portland cement -- which is why it makes such a bad choice for
      > refractory). Up around 400F, it dehydrates to the hemihydrate ("half
      > hydrate"), losing 75% of the chemically combined water.
      > 3. Second chemical dehydration: up around 1000F, the rest of the water is
      > given up, resulting in straight-up calcium sulfate.
      > 4. Calcium sulfate itself decomposes above 2400F or so, giving off stinky
      > SO2 gas (and potentially contaminating whatever metal is touching it),
      > leaving lime (calcium oxide), if additives don't react first (for example,
      > if silica is present, it'll start to form glass).
      >
      > If you're pouring a metal at a temperature less than 100F below the next
      > dehydration point, you must calcine the mold at least past the preceeding
      > stage. The mold does not necessarily have to be heated all the way to the
      > pouring temperature.
      >
      > Examples:
      > - Solder might not need a calcined mold at all. With a melting point
      > around 350F, it's close (it might get bubbly), but may be achieved with
      > only basic dehydration of the mold (say, 250F throughout?).
      >
      > - Lead and zinc can be cast comfortably in a mold baked out at 450F for
      > several hours. Zinc is close, with a pouring temp of maybe 900F, close to
      > the 1000F dehydration point. But as long as it isn't too hot, you need
      > only complete the first dehydration to pour successfully.
      >
      > - Aluminum, and other nonferrous alloys like bronzes, with pouring temps
      > over 1200F, require that the mold be calcined past 1000F (usually to the
      > point where residual soot burns off, which is around red heat -- more than
      > good enough). A very open mold might turn out passable with only the
      > first stage, but don't count on it. (Once upon a time, I cast a pulley in
      > a sand mold, forming the grooves with PoP core inserts. I had baked them
      > thoroughly at 450F just before assembling the mold. The casting worked,
      > but the grooves were obviously distorted by the steam given off by that
      > pesky half a hydration.)
      >
      > - Iron and steel cannot be poured in PoP molds because the stuff fully
      > decomposes over 2500F (causing more gas, shrinkage and cracking), and the
      > sulfurous gasses will react with iron to form sulfide impurities, which
      > cause embrittlement.
      >
      > HTH,
      >
      > Tim
      >
      > --- In hobbicast@yahoogroups.com, "crashbone256" <wheezer606@...> wrote:
      >>
      >> Group:
      >>
      >> I made the mold from eps. I taped the edges with masking tape.
      >> I encased the mold in POP. The mold was oven dried at 170 F for 12 hours.
      >> Then 8 hours at 200 F. Acetone was poured into the mold the dissolve the
      >> styrofoam. The mold was dried at 210 F for 3 hours. The 200F molds were
      >> buried in new dry sand to near the top.
      >>
      >> 5 # Al muffins were melted in a 10 # crucible. The crux was red hot when
      >> removed.
      >>
      >> As the Al melt was poured into the "empty" mold it bubbled and popped and
      >> blew
      >> bubbles up through the sprue. A steady stream was being poured, but it
      >> didn't want to go down the sprue.
      >>
      >> You can see from the first picture how it was gated.
      >> Sprued on the top, Al runs down into the mold and rises off the bottom.
      >>
      >> The casting is porous and crappy.
      >> What to do next time?
      >>
      >>
      >> Thanks
      >> lance
      >> ++++
      >>
      >>
      >> http://groups.yahoo.com/group/hobbicast/photos/album/1891226731/pic/list
      >>
      >
      >
      >
      >
      > ------------------------------------
      >
      > For discussion of Metal Casting and related issues
      > this list does not accept attachments.
      >
      > Files area and list services are at:
      > http://groups.yahoo.com/group/hobbicast
      >
      > For additional files and photos and off topic discussions
      > check out these two affiliated sites:
      > http://groups.yahoo.com/group/sandcrabs
      > http://groups.yahoo.com/group/Hobbicast1
      >
      > Please visit our sponsor: Budget Casting Supply
      > http://budgetcastingsupply.com/
      >
      > List Owner:
      > owly@...
      >
      > Yahoo! Groups Links
      >
      >
      >
      >
      > -----
      > No virus found in this message.
      > Checked by AVG - www.avg.com
      > Version: 2013.0.3272 / Virus Database: 3162/6235 - Release Date: 04/09/13
      >
    • Ron Thompson
      ... Plaster Of Paris. -- Ron Thompson On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA Think, Draw, Print. 3D printers ROCK!
      Message 2 of 24 , Apr 10, 2013
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        On 4/10/2013 3:54 AM, David Hair wrote:
        > I've been reading the last few post about POP molds.
        > HELP, what is POP. I guess you can tell I'm green at this.
        >
        > DH
        > ----- Original Message -----
        > From: "tmoranwms" <tmoranwms@... <mailto:tmoranwms%40charter.net>>
        > To: <hobbicast@yahoogroups.com <mailto:hobbicast%40yahoogroups.com>>
        > Sent: Wednesday, April 10, 2013 2:16 AM
        > Subject: [hobbicast] Re: Need advice
        >
        > > PoP dries out in three stages:
        Plaster Of Paris.

        --


        Ron Thompson
        On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA

        Think, Draw, Print. 3D printers ROCK!

        http://www.plansandprojects.com/My%20Machines/PrusaMendel2012-1/

        http://www.plansandprojects.com My hobby pages are here:
        http://www.plansandprojects.com/My%20Machines/

        Visit the castinghobby FAQ:
        http://castinghobbyfaq.bareboogerhost.com/








        [Non-text portions of this message have been removed]
      • Dennis
        Good recap of the process. Here is the a manufactures description http://www.gp.com/build/product.aspx?pid=1569 I have poured zinc (900 degree) into POP
        Message 3 of 24 , Apr 10, 2013
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          Good recap of the process. Here is the a manufactures' description
          http://www.gp.com/build/product.aspx?pid=1569 I have poured zinc (900
          degree) into POP molds that were dried in the kitchen oven.

          Dennis Cranston
          Houston, Texas


          -----Original Message-----
          From: hobbicast@yahoogroups.com [mailto:hobbicast@yahoogroups.com] On Behalf
          Of tmoranwms
          Sent: Wednesday, April 10, 2013 1:17 AM
          To: hobbicast@yahoogroups.com
          Subject: [hobbicast] Re: Need advice

          PoP dries out in three stages:
          1. Absorbed moisture. This is mostly driven off at any temperature with low
          humidity (with the dry air around here in winter, it would be enough to
          leave a mold sitting out for a few weeks to fully dry!), or over 212F at any
          humidity.
          2. First chemical dehydration: when PoP sets, it forms a chemical dihydrate
          (it's the hydrating process that makes it set, which is also true of
          Portland cement -- which is why it makes such a bad choice for refractory).
          Up around 400F, it dehydrates to the hemihydrate ("half hydrate"), losing
          75% of the chemically combined water.
          3. Second chemical dehydration: up around 1000F, the rest of the water is
          given up, resulting in straight-up calcium sulfate.
          4. Calcium sulfate itself decomposes above 2400F or so, giving off stinky
          SO2 gas (and potentially contaminating whatever metal is touching it),
          leaving lime (calcium oxide), if additives don't react first (for example,
          if silica is present, it'll start to form glass).

          If you're pouring a metal at a temperature less than 100F below the next
          dehydration point, you must calcine the mold at least past the preceeding
          stage. The mold does not necessarily have to be heated all the way to the
          pouring temperature.

          Examples:
          - Solder might not need a calcined mold at all. With a melting point around
          350F, it's close (it might get bubbly), but may be achieved with only basic
          dehydration of the mold (say, 250F throughout?).

          - Lead and zinc can be cast comfortably in a mold baked out at 450F for
          several hours. Zinc is close, with a pouring temp of maybe 900F, close to
          the 1000F dehydration point. But as long as it isn't too hot, you need only
          complete the first dehydration to pour successfully.

          - Aluminum, and other nonferrous alloys like bronzes, with pouring temps
          over 1200F, require that the mold be calcined past 1000F (usually to the
          point where residual soot burns off, which is around red heat -- more than
          good enough). A very open mold might turn out passable with only the first
          stage, but don't count on it. (Once upon a time, I cast a pulley in a sand
          mold, forming the grooves with PoP core inserts. I had baked them
          thoroughly at 450F just before assembling the mold. The casting worked, but
          the grooves were obviously distorted by the steam given off by that pesky
          half a hydration.)

          - Iron and steel cannot be poured in PoP molds because the stuff fully
          decomposes over 2500F (causing more gas, shrinkage and cracking), and the
          sulfurous gasses will react with iron to form sulfide impurities, which
          cause embrittlement.

          HTH,

          Tim

          --- In hobbicast@yahoogroups.com, "crashbone256" <wheezer606@...> wrote:
          >
          > Group:
          >
          > I made the mold from eps. I taped the edges with masking tape.
          > I encased the mold in POP. The mold was oven dried at 170 F for 12 hours.
          > Then 8 hours at 200 F. Acetone was poured into the mold the dissolve
          > the styrofoam. The mold was dried at 210 F for 3 hours. The 200F molds
          were buried in new dry sand to near the top.
          >
          > 5 # Al muffins were melted in a 10 # crucible. The crux was red hot when
          removed.
          >
          > As the Al melt was poured into the "empty" mold it bubbled and popped
          > and blew bubbles up through the sprue. A steady stream was being poured,
          but it didn't want to go down the sprue.
          >
          > You can see from the first picture how it was gated.
          > Sprued on the top, Al runs down into the mold and rises off the bottom.
          >
          > The casting is porous and crappy.
          > What to do next time?
          >
          >
          > Thanks
          > lance
          > ++++
          >
          >
          > http://groups.yahoo.com/group/hobbicast/photos/album/1891226731/pic/li
          > st
          >




          ------------------------------------

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          For additional files and photos and off topic discussions check out these
          two affiliated sites:
          http://groups.yahoo.com/group/sandcrabs
          http://groups.yahoo.com/group/Hobbicast1

          Please visit our sponsor: Budget Casting Supply
          http://budgetcastingsupply.com/

          List Owner:
          owly@...

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        • Dan Brewer
          On of the problems with using POP is that it is hygroscopic meaning that the material will never release all of the water trapped in its structure. It actually
          Message 4 of 24 , Apr 10, 2013
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            On of the problems with using POP is that it is hygroscopic meaning that
            the material will never release all of the water trapped in its structure.
            It actually will draw water out of the atmosphere . I would use a material
            that when fired will vitrify and change to a substance that now will reject
            water. American plaster makes casting plaster. 50 lbs goes for about
            20USD . There are several others. Plaster of Paris is best left to the
            art casting for statues.

            Dan in Auburn


            On Tue, Apr 9, 2013 at 10:07 PM, Eggleston Lance <wheezer606@...>wrote:

            > **
            >
            >
            > OK, will dry 400-700 F.
            >
            > Would it work better to fill from the bottom and
            > vent at the top ?
            >
            > lance
            > ++++
            >
            > On Apr 9, 2013, at 10:19 PM, Jeshua Lacock wrote:
            >
            > > Sounds like the POP had far too much water in it still.
            > >
            > > I would dry it out more around 400F. When I do lost plastic casting (a
            > bit different of course) I heat the POP mold up to around 1000F...
            >
            > [Non-text portions of this message have been removed]
            >
            >
            >


            [Non-text portions of this message have been removed]
          • Yvanwolvesbane
            Hey there, folks- PoP I m familiar with. This is the first time I ve heard of American Plaster. Is it known by other names? What makes it different from PoP?
            Message 5 of 24 , Apr 10, 2013
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              Hey there, folks-
              PoP I'm familiar with. This is the first time I've heard of American Plaster. Is it known by other names? What makes it different from PoP?

              Mark Feldmann/
              Yvan Wolvesbane

              Pacifist with occasional lapses


              On Apr 10, 2013, at 9:52 AM, Dan Brewer <danqualman@...> wrote:

              > On of the problems with using POP is that it is hygroscopic meaning that
              > the material will never release all of the water trapped in its structure.
              > It actually will draw water out of the atmosphere . I would use a material
              > that when fired will vitrify and change to a substance that now will reject
              > water. American plaster makes casting plaster. 50 lbs goes for about
              > 20USD . There are several others. Plaster of Paris is best left to the
              > art casting for statues.
              >
              > Dan in Auburn
              >
              >
              > On Tue, Apr 9, 2013 at 10:07 PM, Eggleston Lance <wheezer606@...>wrote:
              >
              >> **
              >>
              >>
              >> OK, will dry 400-700 F.
              >>
              >> Would it work better to fill from the bottom and
              >> vent at the top ?
              >>
              >> lance
              >> ++++
              >>
              >> On Apr 9, 2013, at 10:19 PM, Jeshua Lacock wrote:
              >>
              >>> Sounds like the POP had far too much water in it still.
              >>>
              >>> I would dry it out more around 400F. When I do lost plastic casting (a
              >> bit different of course) I heat the POP mold up to around 1000F...
              >>
              >> [Non-text portions of this message have been removed]
              >>
              >>
              >>
              >
              >
              > [Non-text portions of this message have been removed]
              >
              >
              >
              > ------------------------------------
              >
              > For discussion of Metal Casting and related issues
              > this list does not accept attachments.
              >
              > Files area and list services are at:
              > http://groups.yahoo.com/group/hobbicast
              >
              > For additional files and photos and off topic discussions
              > check out these two affiliated sites:
              > http://groups.yahoo.com/group/sandcrabs
              > http://groups.yahoo.com/group/Hobbicast1
              >
              > Please visit our sponsor: Budget Casting Supply
              > http://budgetcastingsupply.com/
              >
              > List Owner:
              > owly@...
              >
              > Yahoo! Groups Links
              >
              >
              >
            • Inventor
              Just a side thought: Did you de-gass before the pour? Grandpa Bill
              Message 6 of 24 , Apr 10, 2013
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                Just a side thought:
                Did you de-gass before the pour?

                Grandpa Bill

                --- In hobbicast@yahoogroups.com, "crashbone256" <wheezer606@...> wrote:
                >
                > Group:
                >
                > I made the mold from eps. I taped the edges with masking tape.
                > I encased the mold in POP. The mold was oven dried at 170 F for 12 hours.
                > Then 8 hours at 200 F. Acetone was poured into the mold the dissolve the
                > styrofoam. The mold was dried at 210 F for 3 hours. The 200F molds were buried in new dry sand to near the top.
                >
                > 5 # Al muffins were melted in a 10 # crucible. The crux was red hot when removed.
                >
                > As the Al melt was poured into the "empty" mold it bubbled and popped and blew
                > bubbles up through the sprue. A steady stream was being poured, but it didn't want to go down the sprue.
                >
                > You can see from the first picture how it was gated.
                > Sprued on the top, Al runs down into the mold and rises off the bottom.
                >
                > The casting is porous and crappy.
                > What to do next time?
                >
                >
                > Thanks
                > lance
                > ++++
                >
                >
                > http://groups.yahoo.com/group/hobbicast/photos/album/1891226731/pic/list
                >
              • StoneTool
                Mark: I think you misread.......... American Plaster is probably a company not a product. Though I wouldn t be surprised if during the Bush administration
                Message 7 of 24 , Apr 10, 2013
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                  Mark:
                  I think you misread.......... American Plaster is probably a
                  company not a product. Though I wouldn't be surprised if during the
                  Bush administration when they were stirring up hatred against the French
                  for telling the truth, and going to such absurd lengths as renaming
                  everything with the word "French", if Plaster of Paris wasn't renamed
                  "American Plaster" along with the other childish nonsense that went on!

                  Howard

                  On 04/10/2013 09:42 AM, Yvanwolvesbane wrote:
                  > Hey there, folks-
                  > PoP I'm familiar with. This is the first time I've heard of American Plaster. Is it known by other names? What makes it different from PoP?
                  >
                  > Mark Feldmann/
                  > Yvan Wolvesbane
                  >
                  > Pacifist with occasional lapses
                  >
                  >
                  > On Apr 10, 2013, at 9:52 AM, Dan Brewer <danqualman@...> wrote:
                  >
                  >> On of the problems with using POP is that it is hygroscopic meaning that
                  >> the material will never release all of the water trapped in its structure.
                  >> It actually will draw water out of the atmosphere . I would use a material
                  >> that when fired will vitrify and change to a substance that now will reject
                  >> water. American plaster makes casting plaster. 50 lbs goes for about
                  >> 20USD . There are several others. Plaster of Paris is best left to the
                  >> art casting for statues.
                  >>
                  >> Dan in Auburn
                  >>
                  >>
                  >> On Tue, Apr 9, 2013 at 10:07 PM, Eggleston Lance <wheezer606@...>wrote:
                  >>
                  >>> **
                  >>>
                  >>>
                  >>> OK, will dry 400-700 F.
                  >>>
                  >>> Would it work better to fill from the bottom and
                  >>> vent at the top ?
                  >>>
                  >>> lance
                  >>> ++++
                  >>>
                  >>> On Apr 9, 2013, at 10:19 PM, Jeshua Lacock wrote:
                  >>>
                  >>>> Sounds like the POP had far too much water in it still.
                  >>>>
                  >>>> I would dry it out more around 400F. When I do lost plastic casting (a
                  >>> bit different of course) I heat the POP mold up to around 1000F...
                  >>>
                  >>> [Non-text portions of this message have been removed]
                  >>>
                  >>>
                  >>>
                  >>
                  >> [Non-text portions of this message have been removed]
                  >>
                  >>
                  >>
                  >> ------------------------------------
                  >>
                  >> For discussion of Metal Casting and related issues
                  >> this list does not accept attachments.
                  >>
                  >> Files area and list services are at:
                  >> http://groups.yahoo.com/group/hobbicast
                  >>
                  >> For additional files and photos and off topic discussions
                  >> check out these two affiliated sites:
                  >> http://groups.yahoo.com/group/sandcrabs
                  >> http://groups.yahoo.com/group/Hobbicast1
                  >>
                  >> Please visit our sponsor: Budget Casting Supply
                  >> http://budgetcastingsupply.com/
                  >>
                  >> List Owner:
                  >> owly@...
                  >>
                  >> Yahoo! Groups Links
                  >>
                  >>
                  >>
                  >
                  > ------------------------------------
                  >
                  > For discussion of Metal Casting and related issues
                  > this list does not accept attachments.
                  >
                  > Files area and list services are at:
                  > http://groups.yahoo.com/group/hobbicast
                  >
                  > For additional files and photos and off topic discussions
                  > check out these two affiliated sites:
                  > http://groups.yahoo.com/group/sandcrabs
                  > http://groups.yahoo.com/group/Hobbicast1
                  >
                  > Please visit our sponsor: Budget Casting Supply
                  > http://budgetcastingsupply.com/
                  >
                  > List Owner:
                  > owly@...
                  >
                  > Yahoo! Groups Links
                  >
                  >
                  >
                  >
                • Dan Brewer
                  The big difference is that when fired the substrate will no longer adsorb any moisture. The term used to describe it is vitrification or to become like glass.
                  Message 8 of 24 , Apr 10, 2013
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                    The big difference is that when fired the substrate will no longer adsorb
                    any moisture. The term used to describe it is vitrification or to become
                    like glass.


                    On Wed, Apr 10, 2013 at 8:42 AM, Yvanwolvesbane <yvanwolvesbane222@...
                    > wrote:

                    > **
                    >
                    >
                    > Hey there, folks-
                    > PoP I'm familiar with. This is the first time I've heard of American
                    > Plaster. Is it known by other names? What makes it different from PoP?
                    >
                    > Mark Feldmann/
                    > Yvan Wolvesbane
                    >
                    > Pacifist with occasional lapses
                    >
                    >
                    > On Apr 10, 2013, at 9:52 AM, Dan Brewer <danqualman@...> wrote:
                    >
                    > > On of the problems with using POP is that it is hygroscopic meaning that
                    > > the material will never release all of the water trapped in its
                    > structure.
                    > > It actually will draw water out of the atmosphere . I would use a
                    > material
                    > > that when fired will vitrify and change to a substance that now will
                    > reject
                    > > water. American plaster makes casting plaster. 50 lbs goes for about
                    > > 20USD . There are several others. Plaster of Paris is best left to the
                    > > art casting for statues.
                    > >
                    > > Dan in Auburn
                    > >
                    > >
                    > > On Tue, Apr 9, 2013 at 10:07 PM, Eggleston Lance <wheezer606@...
                    > >wrote:
                    > >
                    > >> **
                    >
                    > >>
                    > >>
                    > >> OK, will dry 400-700 F.
                    > >>
                    > >> Would it work better to fill from the bottom and
                    > >> vent at the top ?
                    > >>
                    > >> lance
                    > >> ++++
                    > >>
                    > >> On Apr 9, 2013, at 10:19 PM, Jeshua Lacock wrote:
                    > >>
                    > >>> Sounds like the POP had far too much water in it still.
                    > >>>
                    > >>> I would dry it out more around 400F. When I do lost plastic casting (a
                    > >> bit different of course) I heat the POP mold up to around 1000F...
                    > >>
                    > >> [Non-text portions of this message have been removed]
                    > >>
                    > >>
                    > >>
                    > >
                    > >
                    > > [Non-text portions of this message have been removed]
                    > >
                    > >
                    > >
                    > > ------------------------------------
                    >
                    > >
                    > > For discussion of Metal Casting and related issues
                    > > this list does not accept attachments.
                    > >
                    > > Files area and list services are at:
                    > > http://groups.yahoo.com/group/hobbicast
                    > >
                    > > For additional files and photos and off topic discussions
                    > > check out these two affiliated sites:
                    > > http://groups.yahoo.com/group/sandcrabs
                    > > http://groups.yahoo.com/group/Hobbicast1
                    > >
                    > > Please visit our sponsor: Budget Casting Supply
                    > > http://budgetcastingsupply.com/
                    > >
                    > > List Owner:
                    > > owly@...
                    > >
                    > > Yahoo! Groups Links
                    > >
                    > >
                    > >
                    >
                    >
                    >


                    [Non-text portions of this message have been removed]
                  • Yvanwolvesbane
                    Thanks, Dan. That was very clear & warrants further investigation. Mark Feldmann/ Yvan Wolvesbane Pacifist ...with occasional lapses.
                    Message 9 of 24 , Apr 10, 2013
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                      Thanks, Dan. That was very clear & warrants further investigation.

                      Mark Feldmann/
                      Yvan Wolvesbane

                      Pacifist ...with occasional lapses.


                      On Apr 10, 2013, at 4:21 PM, Dan Brewer <danqualman@...> wrote:

                      > The big difference is that when fired the substrate will no longer adsorb
                      > any moisture. The term used to describe it is vitrification or to become
                      > like glass.
                      >>
                      >>
                      >>
                      >>
                      >>
                      >>
                      >>>
                      >>>
                      >>>
                      >>>>
                      >>>>
                      >>>>
                      >>>>
                      >>>>
                      >>>>>
                      >>>>
                      >>>>
                      >>>>
                      >>>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>>
                      >>
                      >>
                      >>
                    • Inventor
                      Hey Dan, About a half a dozen links wouldn t hurt.... A few to read up about it. A few more as to where to buy it for 20 BUCKS All I ve found was clay and
                      Message 10 of 24 , Apr 11, 2013
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                        Hey Dan,
                        About a half a dozen links wouldn't hurt....
                        A few to read up about it.
                        A few more as to where to buy it for "20 BUCKS"

                        All I've found was clay and that 'started' at $85/50#.

                        Grandpa Bill

                        --- In hobbicast@yahoogroups.com, Dan Brewer <danqualman@...> wrote:
                        >
                        > On of the problems with using POP is that it is hygroscopic meaning that
                        > the material will never release all of the water trapped in its structure.
                        > It actually will draw water out of the atmosphere . I would use a material
                        > that when fired will vitrify and change to a substance that now will reject
                        > water. American plaster makes casting plaster. 50 lbs goes for about
                        > 20USD . There are several others. Plaster of Paris is best left to the
                        > art casting for statues.
                        >
                        > Dan in Auburn
                      • Dan Brewer
                        So here is a link to one supplier. http://www.sheffield-pottery.com/U-S-Gypsum-1-CASTING-PLASTER-50-lbs-p/rmcaspla50.htm The name of the company is US gypsum
                        Message 11 of 24 , Apr 11, 2013
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                          So here is a link to one supplier.
                          http://www.sheffield-pottery.com/U-S-Gypsum-1-CASTING-PLASTER-50-lbs-p/rmcaspla50.htm
                          The name of the company is US gypsum not US plaster. Brain fart. The way
                          that I use it is to take my wax master with sprus and vent attached and
                          coat it in Jet dry. Yes the stuff you use in your dish washer. It breaks
                          the surface tension on the wax and allows the plaster to stick. I mix a
                          little of the plaster up to the consistency of thin pancake batter and
                          paint it on. until I have coated the entire master except the top of the
                          pouring cup and the top of the vents. . I let that dry a little miz a
                          little more up a little thicker and put on another coat. When still wet I
                          sprinkle flint sand on the entire piece. Let that dry for a little. Mix up
                          some more plaster about 60/40 plaster sand and coat the piece. Let dry. You
                          should have coated the piece about 1.4 to 1/2 inch thick by now. Mix up
                          some more plaster 50/50 sand and plaster. sprinkle each coat with sand. The
                          next coat should be 30/30/30 plaster /sand / and grog. Grog is previously
                          fired plaster that has been broken up in to pieces that will fit through a
                          #8 sieve. When you have 3/4 to one inch of plaster wrap the piece in small
                          chicken wire. This is to keep the mold from breaking up when you fire it.
                          Add another inch of plaster , grog, sand to the outside of the mold. The
                          top and bottom of the mold should be able to support the mold with out
                          tipping over. The top because when you fire it the top will be down so all
                          of the wax will leave the mold and the bottom so you can fill the now
                          vacated mold with metal. Let dry .for several days in a warm spot. I place
                          mine on a blotter board. My blotter board is a 2x2 piece of drywall.
                          Place in your kiln and heat at the rate of 100 deg f per hour until the
                          melting temp of the wax has been reached. My kiln has a stainless steel
                          sink in the bottom that is plumbed out the bottom to get some of the wax
                          out of the kiln. I am able to recover some of it but not much. after the
                          wax is out around 200 to 275 deg you can ramp up a little faster Fire at
                          2000deg f for 4 to 20 hours depending on size of the piece. Let cool to
                          around 400 deg and pour.. Cover the pouring cup and vents with perlite or
                          vermiculite and let cool. When the outside of the mold is just hot enough
                          to touch sweep off the perlite/ vermiculite and you can remove the
                          plaster. Remember that it will be hot. I use a hammer and a water hose to
                          remove most of the plaster . Plaster will clog your drain . More clean up
                          can be done with a stiff brush or sand blasting.
                          For more information look up lost wax casting , ceramic shell casting.

                          Dan in Auburn

                          Other places to find casting plaster are pottery suppl houses. jewelery
                          supply houses. And there are lots of formulas of the casting plaster. This
                          is just the one that I have been using.


                          On Thu, Apr 11, 2013 at 11:56 AM, Inventor <welfab@...> wrote:

                          > **
                          >
                          >
                          > Hey Dan,
                          > About a half a dozen links wouldn't hurt....
                          > A few to read up about it.
                          > A few more as to where to buy it for "20 BUCKS"
                          >
                          > All I've found was clay and that 'started' at $85/50#.
                          >
                          > Grandpa Bill
                          >
                          >
                          > --- In hobbicast@yahoogroups.com, Dan Brewer <danqualman@...> wrote:
                          > >
                          > > On of the problems with using POP is that it is hygroscopic meaning that
                          > > the material will never release all of the water trapped in its
                          > structure.
                          > > It actually will draw water out of the atmosphere . I would use a
                          > material
                          > > that when fired will vitrify and change to a substance that now will
                          > reject
                          > > water. American plaster makes casting plaster. 50 lbs goes for about
                          > > 20USD . There are several others. Plaster of Paris is best left to the
                          > > art casting for statues.
                          > >
                          > > Dan in Auburn
                          >
                          >
                          >


                          [Non-text portions of this message have been removed]
                        • abascirocco
                          FWIW, US Gypsum also has a plaster specifically formulated for non-ferrous metal casting, they call it simply USG metal casting plaster. The other major North
                          Message 12 of 24 , Apr 11, 2013
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                            FWIW, US Gypsum also has a plaster specifically formulated for non-ferrous metal casting, they call it simply USG metal casting plaster. The other major North American plaster manufacturer is Georgia Pacific, they also have a line of metal casting plasters.



                            --- In hobbicast@yahoogroups.com, Dan Brewer <danqualman@...> wrote:
                            >
                            > So here is a link to one supplier.
                            > http://www.sheffield-pottery.com/U-S-Gypsum-1-CASTING-PLASTER-50-lbs-p/rmcaspla50.htm
                            > The name of the company is US gypsum not US plaster. Brain fart. The way
                            > that I use it is to take my wax master with sprus and vent attached and
                            > coat it in Jet dry. Yes the stuff you use in your dish washer. It breaks
                            > the surface tension on the wax and allows the plaster to stick. I mix a
                            > little of the plaster up to the consistency of thin pancake batter and
                            > paint it on. until I have coated the entire master except the top of the
                            > pouring cup and the top of the vents. . I let that dry a little miz a
                            > little more up a little thicker and put on another coat. When still wet I
                            > sprinkle flint sand on the entire piece. Let that dry for a little. Mix up
                            > some more plaster about 60/40 plaster sand and coat the piece. Let dry. You
                            > should have coated the piece about 1.4 to 1/2 inch thick by now. Mix up
                            > some more plaster 50/50 sand and plaster. sprinkle each coat with sand. The
                            > next coat should be 30/30/30 plaster /sand / and grog. Grog is previously
                            > fired plaster that has been broken up in to pieces that will fit through a
                            > #8 sieve. When you have 3/4 to one inch of plaster wrap the piece in small
                            > chicken wire. This is to keep the mold from breaking up when you fire it.
                            > Add another inch of plaster , grog, sand to the outside of the mold. The
                            > top and bottom of the mold should be able to support the mold with out
                            > tipping over. The top because when you fire it the top will be down so all
                            > of the wax will leave the mold and the bottom so you can fill the now
                            > vacated mold with metal. Let dry .for several days in a warm spot. I place
                            > mine on a blotter board. My blotter board is a 2x2 piece of drywall.
                            > Place in your kiln and heat at the rate of 100 deg f per hour until the
                            > melting temp of the wax has been reached. My kiln has a stainless steel
                            > sink in the bottom that is plumbed out the bottom to get some of the wax
                            > out of the kiln. I am able to recover some of it but not much. after the
                            > wax is out around 200 to 275 deg you can ramp up a little faster Fire at
                            > 2000deg f for 4 to 20 hours depending on size of the piece. Let cool to
                            > around 400 deg and pour.. Cover the pouring cup and vents with perlite or
                            > vermiculite and let cool. When the outside of the mold is just hot enough
                            > to touch sweep off the perlite/ vermiculite and you can remove the
                            > plaster. Remember that it will be hot. I use a hammer and a water hose to
                            > remove most of the plaster . Plaster will clog your drain . More clean up
                            > can be done with a stiff brush or sand blasting.
                            > For more information look up lost wax casting , ceramic shell casting.
                            >
                            > Dan in Auburn
                            >
                            > Other places to find casting plaster are pottery suppl houses. jewelery
                            > supply houses. And there are lots of formulas of the casting plaster. This
                            > is just the one that I have been using.
                            >
                            >
                            > On Thu, Apr 11, 2013 at 11:56 AM, Inventor <welfab@...> wrote:
                            >
                            > > **
                            > >
                            > >
                            > > Hey Dan,
                            > > About a half a dozen links wouldn't hurt....
                            > > A few to read up about it.
                            > > A few more as to where to buy it for "20 BUCKS"
                            > >
                            > > All I've found was clay and that 'started' at $85/50#.
                            > >
                            > > Grandpa Bill
                            > >
                            > >
                            > > --- In hobbicast@yahoogroups.com, Dan Brewer <danqualman@> wrote:
                            > > >
                            > > > On of the problems with using POP is that it is hygroscopic meaning that
                            > > > the material will never release all of the water trapped in its
                            > > structure.
                            > > > It actually will draw water out of the atmosphere . I would use a
                            > > material
                            > > > that when fired will vitrify and change to a substance that now will
                            > > reject
                            > > > water. American plaster makes casting plaster. 50 lbs goes for about
                            > > > 20USD . There are several others. Plaster of Paris is best left to the
                            > > > art casting for statues.
                            > > >
                            > > > Dan in Auburn
                            > >
                            > >
                            > >
                            >
                            >
                            > [Non-text portions of this message have been removed]
                            >
                          • bs190815
                            For years I have been using Ransom & Randoph Ultra-Vest. I recently bought five 100 pound drum; I use nothing else! Here is their web site, lots of good
                            Message 13 of 24 , Apr 18, 2013
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                              For years I have been using Ransom & Randoph Ultra-Vest. I recently bought five 100 pound drum; I use nothing else!

                              Here is their web site, lots of good information.

                              http://www.ransom-randolph.com/
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