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Thread: Plaster Mold Help?

  1. #1

    Plaster Mold Help?

    So Iím working on a small scale sheet mold for gauntlets and things and my first test failed miserably. So before I try again I thought Iíd figure out a full rundown of where I went wrong.

    So I made a small scale sheet out of foam punched circles, glued them down to cardboard.

    1. My glue should have been stronger I think.

    I made a mold box out of cardboard.

    2. Was cardboard a bad way to go?

    I mixed up some plaster. Dap Plaster of Paris.

    3. Was this the wrong plaster? I am fairly sure I mixed it wrong and didnít mix enough.

    I sprayed it with some mold release.

    4. This was me being lazy. It was not a good enough mold release. Apparently I can use watered down Vaseline?

    My mold was thin and cracked and didnít want to come off the cardboard or some of the circles.

    So. I know I messed up the mixing and the mold release and Iíve searched around and found answers for that. But I guess I just wanna know:

    Is cardboard an okay mold box base?

    What plaster do I need and how thick should it be?

    Thanks to anymer that helps out.



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  2. #2
    Senior Member North Pacific Pod
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    Definitely do not use cardboard. Thin wood should be easy to get and cheap ^_^
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  3. #3
    Senior Member Pod of Cali Merman Storm's Avatar
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    I would use plywood for the base, or several layers of cardboard glued together. You want something stiff enough that it will not bend under the weight of the plaster. Assume the plaster sheet is not strong enough to support its own weight if you pick it up by a corner.

    Also, look at the scale sheet: is there a way for the plaster to get under the scales, so it gets caught? All such gaps need to be filled. (I'd use West Systems Epoxy, as that is what I happen to have in my shop, but most any non-shrinking glue will work.)
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  4. #4
    Thank you both! That definitely addresses two major problems I had last time. The plaster stuck to the cardboard AND got under the scales. I will definitely fix those.


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  5. #5
    Senior Member North Pacific Pod
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    Ive found cardboard can suck up certain substances if not specially coated. Please post lots of updates ^_^
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  6. #6
    I find Plaster of Paris is fairly easy to crack even when properly cured. It's not a bad idea to have a thick base for a mold if necessary. Just make sure you mix well and pour it in one go. Not layers. It helps stability and will keep out compromising air bubbles.

  7. #7
    Senior Member Undisclosed Pod
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    Another thing you can possibly do to strengthen the mould is as you pour - add in layers of burlap after the item being cast is fully covered (while the plaster is fresh) - then tap the sides of your mold box to shake out air bubbles. The burlap could help strengthen the plaster, and keep it from completely shattering. You still wouldn't want to pick it up in a manner that puts pressure on the center or a corner though.

  8. #8
    That sounds good.

    Is there something other than plaster I should be using that would be more durable? I know silicone can be tricky to get out.


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