"That's the Cup of a Carpenter"—My Holy Grail Build

[PhantomForge]

So the problem is that the resin foamed the first time around (which it never did in past projects) and pushed out parts of the mold that weren't completely secured by the plaster mother mold. I thought this was a problem with the resin being rather old, but the same thing happened this time around with brand new resin.

Anyone have any advice on how to fix this?
It's fairly humid right now, is that effecting the resin curing process?

 

[Customrelic]

What type of casting resin are you using? Ive never had it "push" on a mold before. Are you securing the mothermold with bands?

 

[PhantomForge]

What type of casting resin are you using? Ive never had it "push" on a mold before. Are you securing the mothermold with bands?

I'm using polyurethane resin. The reason it was pushing out the mold was because I have a sort of cork that I plug in the top, and when the resin began foaming and expanding, it had no place to go so it expanded the silicone mold.
Yes, I secured the mothermold with bands, but I usually don't have this sort of problem where the resin foams. I've used this resin before, and it usually doesn't foam when it's drying.

I'm going to try slush casting it first, because small layers don't seem to foam, and then pouring more resin in afterwards. But, before that I'm going to take a bit of a break on this project. I'm taking a pottery class and have access to a pottery wheel and clay, so I'm going to spend my free time at the moment making an actual ceramic holy grail.