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model coating

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  • model coating

    Hi; this is my first post, so I would greet the users.
    I made some models in clay, which are hardened now (not baked; they are still raw); I would get plaster molds from them, but so far the previous models was melted by the wet plaster poured upon them, whatever the amount of water put in the plaster mix. Do you know something to impermeabilize them?

  • #2
    Hello and to the forum. Sorry I can't help you with your problem, I'm sure someone will be along soon who knows about this stuff.

    Jo x
    Things to make and do
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    • #3

      Hi Marcello,

      Welcome to the forum.

      Normally, you pour the mould over the model before it starts drying. This allows you to easily remove the model from the mould.But there is a chance for you to damage the model in the process. You need not worry too much about this as you can always make a new one using your mould. If the model is dry, it will absorb the water from the plaster and get damaged.

      To get the plaster consistency right
      1. Start sprinkling plaster on the water (please wear a mask if you have one, otherwise try not to create or inhale plaster dust)
      2. Allow the plaster to sink in the water and then sprinkle some more.
      3. Repeat the process until the plaster doesnt get absorbed, but stands on the surface in mounds.
      4. Stir vigourously until there are no lumps in the plaster.
      5. Wait for 1 minute.(I think this is to allow the air bubbles to surface and pop. Someone please correct me if I am wrong)
      6. Pour the plaster on the mould.

      As a general rule, the amount of water used should be half the amount of plaster.

      Hope this helps.

      Good Luck!


      • #4
        Thanks for the warm welcome and the answers. As far as I can get, there is no way to spray some coating stuff (like silicon) upon the crude model, but I have to proceed traditionally by pouring a mix of plaster, albeit a less watery one?


        • #5
          Model Coating

          Hi and welcome to the forum. I would only add to what Kavitha has said, in that you need to make your plaster mould immediately you have created the model (i.e. while it is still wet/leather hard.) If you try to make a mould from a dry unfired model it will soak up the moisture from the plaster and will distort and be very difficult to remove from the mould. Good luck!


          • #6
            I would try to cover the models with some oily substance. It would resist water and stop plaster (mixed with water, as far as I can see) from merging into the model. A thin layer of something like Vaseline could do well, I think.


            • #7
              The problem with vaseline etc is that it tends to get in all the little nooks and crannies and you lose a lot of the fine detail (it would be OK for a plain surface).

              If you pour the mixed (wet) plaster over the mould before it has a chance to dry out it won't absorb the water anyway. As the plaster dries the mould will naturally shrink away from the plaster and will be easy to remove.

              In our experience we make the model, pour over the plaster and leave for 1 - 2 hours then take out the model. We don't have any problems doing this.


              • #8
                I will do some experiments with some substances and I'll make you know. Thank you all for now.