Will Ultracal stick to Pottery Plaster?

So I've had issues with my pottery plaster two part mold where it wouldn't pry open without breaking- I think this was due to the pottery plaster not being strong enough (probably needed to be built up more too) and the fact that there was a slight undercut that I'm now fixing. I'm now basically going to get rid of and then rebuild from scratch all the edges of the plaster. 
The thing is that most of the print coat of the plaster is still in tact and fine and I'd rather build on top of that so I don't have to damage my clay sculpt. I'm wanting to use ultracal this time because I know that it's a lot stronger and has a fairly quick drying time and I'll at least know if strength was the issue or not. Will the Ultracal stick fine to the pottery plaster if I start layering it on top? I'm fine if there are some imperfections etc. I'm really just looking to get it done as soon as possible for a deadline! 
Thank you!


  • I've never tried bonding Ultracal to pottery plaster.  My concern is that since the pottery plaster is already set up and the two formulas are dissimilar, they may not want to bond together.   Slightly dampening the dry plaster can help the two bond together though.

    It's worth trying, especially if your only other option is to start over.

  • Thank you! I'll give it a go. Would another layer of wet pottery plaster before putting on the ultracal help or hinder do you think? 
  • I would just go right to the Ultracal, since it has the strength you are looking for.

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