How to fix leaking plaster mold?

[Sanna]

Hello! Can anyone help me with advise related to casting with clay slip in a plaster mold? I have made a 2-parts mold, and unfortunately there are some tiny holes between the parts, so I can’t tightly close it with rubber bands for casting. Is it possible to use plaster tape or other sealing to prevent clay slip leaking out? Or other tips to repair the holes? Thanks already ☺️

[Chilly]

Try a coil of squidgy clay.  Press it into the join all the way round, from the outside.

If that works, and the final result is good, and you want to reuse the mould a lot, I'd re-make it, or at least one side to get a better seal.

[Jeff Longtin]

Sometimes I combine mold parts to test out new design ideas.  Sometimes the mold parts do not fit well together. I find filling the small holes/gaps with slip, FROM THE OUTSIDE, to be  a simple remedy. Let the slip set up for a few minutes and you have a "sealed" mold.  THEN fill the mold cavity with slip.

You can also fill the gaps from the inside but I find it hard to get my hands inside smaller molds.

 

 

[neilestrick]

Dribble some slip into the cracks from the outside, let it set up, then fill the mold. My concern with adding clay between the mold pieces before assembly is that it's going to be very difficult to get a thin enough layer that won't affect how the mold goes together. It's worth trying both methods, though.

[Chilly]

15 hours ago, neilestrick said:

My concern with adding clay between the mold pieces before assembly is that it's going to be very difficult to get a thin enough layer that won't affect how the mold goes together. It's worth trying both methods, though.

I didn't mean for the clay to be between the plaster, just pushed into the gaps.  Perhaps I should have said " push it into the gaps, not between the plaster"

[neilestrick]

3 hours ago, Chilly said:

I didn't mean for the clay to be between the plaster, just pushed into the gaps.  Perhaps I should have said " push it into the gaps, not between the plaster"

My bad. I misread.

[Sanna]

Thank you all for the great tips! I will try the clay slip from outside. That sounds like it could work. It didn’t occur to me before. 

[Ben xyz]

On 11/22/2021 at 6:29 AM, Sanna said:

Thank you all for the great tips! I will try the clay slip from outside. That sounds like it could work. It didn’t occur to me before. 

1. Did the slip on the outside seam work, Sanna? Having the same problem.
2. Considering Flex or Gorilla Tape, but not sure about adhesion to plaster cast.
3. Maybe coil of non-drying  modeling type clay (similar solve as squidgy clay)?

My large casting (15"x29"x10") was problematic to begin with and can't see making it again. This was my third try and several bags of plaster later. Gallons of slip  leakage over studio floor now on top of it.