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BlackDogPottery

Hump and Slump Molds

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Hey everyone. 

I was looking into making some molds to make slab work with. I was wondering if anyone has heard of using concrete to make the molds from? Ive used plaster in the past and have had some goods results and some not so good results. I think concrete could work as it's absorbent and durable. Love to hear some thoughts.

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I think concrete molds would be mighty heavy and you won't be able to easily alter them if necessary after making them. With plaster you can easily sand out little imperfections in the molds. What was the issue with the plaster molds?

The easiest way to make slump molds is to cut them out of insulating foam board, like the pink your blue stuff from the hardware store. Cut it with a box knife, then clean up the edges with some coarse sandpaper.

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I'll take that into thought. The issue with the plaster was I was unable to get things un-stuck even at leather hard (would then dry to bone dry and crack). Then again I was using hardware store plaster as I couldn't really budget in pottery plaster. 

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If you go to the trouble to make molds use 1# pottery plaster-mold soap can act as a release as well.

Cement will have its own drawbacks and the cost is not much different than quality plaster .

Never used cement as a mold surface-its great to wedge on. Its more weight than dried plaster and will hold water longer.

This maybe reinvent the wheel stuff and I have yet to see square wheels work better than round ones. Let us know how the cement works-it could be the next new thing?

 

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Mold soap is only used as a release when making the original mold, to get the plaster to release from the original. You then have to wash it off and let the plaster dry. You don't want to use mold soap to get the clay to release from the plaster when actually making pieces. You need the plaster to be completely dry before using the mold, which may take a week or two of drying depending on the thickness of the mold ad humidity levels in your studio. Damp plaster is worthless.

Tyler Miller and Rae Reich like this

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