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molding disaster-help

Discussion in 'Molding and Casting' started by NDNHunter, Aug 28, 2007.

  1. NDNHunter

    NDNHunter 2007 World Chamionships, Reno

    Bran new to molding so please bare with. attempted to demold my plaster mold and I had to chisel it apart. I sealed the molds with two coats of clear gloss. waxed two coats with Johnsons one step floor wax, ??? After everything was dry, I sprayed them down with syn-lube, ??? let that dry, then foamed it. obviously not the right procedure, because the foam stuck to the plaster mold. Will candle wax work as a separator? Can I put a thin layer of nonhardening clay inside the mold and foam it, will it foam properly inside the clay? My final casts will be covered in clay anyway before I make the fiberglass molds. Glad I only foamed one mold for a tester. Molding gurus, let me have it! Thanks in advance!
     
  2. ljones

    ljones 1994 wasco award winner

    the only time i would use a plaster mold for foam would be as a one shot or waste mold when you are carcass casting , where you would only expect to get one casting then make a permanate mold from that casting out of fiberglas, to get more than one casting out of a plaster mold you would have to use paper mache or fiberglas resin with glass cloth.
     

  3. Try vaseline in a thin layer after you seal the plaster
     
  4. NDNHunter

    NDNHunter 2007 World Chamionships, Reno

    The molds are carcass casts, I went a little overboard reinforcing them because I wanted to get at least 4-5 casts out of them. I'll try the vaseline, let you know what happens. Thanks! :)
     
  5. newbirdman

    newbirdman New Member

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    Buy some Kerosine and mix 1/2 and 1/2 with melted candle wax . Its cheaper than vaseline since your going to need a lot of it anyway if you plan on making forms . This is the same thing Van dykes sells as a mold release . Rick
     
  6. I have two plaster fox molds (bodies, heads and legs as separate molds) as well as some cotton tails and snowshoe hare molds that I've used several times. I force dry the molds in an oven at 200 degrees for a few hours the day after they are made. I give them another few days to thoroughly dry then do any 'fixin' that needs to be done. I then apply three coats of orange shellac. The next day I apply several coats of Mother's Car Wax - buffing between coats. When I need to make a form I apply two coats of PVA to the entire interior surface of the mold, including the mating surfaces, letting them dry. I then pour the foam and de-mold about 35 to 40 minutes later. Never had a problem with this method. Additional forms just need two more coats of PVA.
     
  7. kbauman

    kbauman Active Member

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    OK
    I use Johnson's Floor Paste all the time and it works like a charm. Good Luck
     
  8. Jim B

    Jim B Active Member

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    Don't be afraid when making plaster carcass cast molds,to slick them up(after they are completely dry) with 80 or 100 grit sandpaper.A lot of times wrinkles in the carcass create ridges in the mold that you don't need plus there can be a host of other rough spots.sand them out before sealing and waxing.I agree with the sealing and several coats of paste wax but have had much better luck NOT buffing between coats especially when casting with foam.Your first pour will always stick worst.Each subsequent pour will be easier.Just don't expect a plaster mold to last through a lot of pours.Always be prepared for the possibility that you may only get one.
     
  9. NDNHunter

    NDNHunter 2007 World Chamionships, Reno

    Hey, Thanks everyone for the help! I just settled for a single cast, I'll worry about extras after I do my fiberglass. DUUHH!!LOL ;D This has been a good education, you guys are great! Thanks!! :)
     
  10. When making any foam cores we'll use 3 coats of green wax then a thin layer of PVA ( If we need to keep a high definition off the mold) a greenwax & mineral spirit combination when making foam cores for injecting parts.
    Darwin
     
  11. Ditto Newbirdman, and Kens "Johnsons Paste Wax" in the yellow flat can.

    Seal the mold with the wax and kerosene, you need to keep sealing it until a wax film is built up, this can take a day or two and use a cotton cloth to polish the mold between the waxing.

    Before the pour polish the inside and the shelf to a gloss with a clean cotton cloth. The shine will left you know the mold is sealed.

    Now use the paste wax for a final waxing and polish it again.

    If you dont want kerosene smell in the shop, seal with several coats of Shellac I use the spray shellac, allow to fully dry between coats, again this will take several days to get the mold sealed. the surface should start to shine.

    Now using a china bristle brush 1/2", cut half the bristels off across them for a stiff brush, using the paste wax, (it's pure carnuba and the only one that works perfectly) wax the mold, allow it to dry buff the mold, wax and repeat.

    Test the mold with a bit of foam of catlyzed bondo, just one side is all you need to test then dont fill it full.

    If it dont pop out you need to wax the mold somemore.

    Anytime a plaster mold does not pop the part out, its not sealed and waxed well enough.

    By the way forget the (sprayed them down with syn-lube) its the wrong product for plaster molds.

    You need candle wax in bulk for sealing the mold!!!!! and then the paste wax for the release agent.

    I even use shellac and paste wax on the bondo molds.

    Even the supply companies have to break in the mold, this requires a couple waxings and a couple castings if its a good mold. The more parts you pull the better the mold will become.