How can I make a watertight two part box mold for ice?

I'm trying to make a mold for an ice project that is a box mold. I want the parting line to be in the middle of the model, and it needs to be watertight because I am using as an ice mold. Any suggestions? Thanks for looking.

Koosie7 years ago
Well, you could smear some Gemkem along the seam and put duct-tape over that.  That should be water tight.

First try just some Gemkem because if it holds the water in, it might just seperate when the ice expands, making it a little bit easier for you to take the two parts apart.

Hope this helps.