Quick question... I'm making a prop knife with the intention of making a mould and casting it. The master was made using a block of casting powder set in the vague shape, then carved into the form of the blade. Issue is the newly-carved surface doesn't feel set! Instructions quoted a 20 minute set time and I left it a good few hours before I started carving, but it's still clammy to the touch. Is this normal or have I screwed up? I'm concerned that I perhaps put too much water in the mix... Any advice is greatly appreciated!!