Has anyone here tried drywall mud, like Smoothset 40, for making molds? It dries semi-hard, shows fine details, and doesn't shrink.
And it gives you almost 30 minutes open working time to get you masters set, and your vent holes in place.
I made my first two piece mold this week with the Smoothset, and it came out alright. It had bubbles and voids beneath the masters, and around them, so I'm going to remake it, and hand butter the plastic masters before I set them in it this time.
I used spray pam to keep the second half from sticking to the first half, and it worked fine.
I plan to coat both halves with diluted carpenter's glue after they cure out, to make them stronger and smoother.
A word of caution about adding glue to either pop, or drywall mud.
Glue makes drywall mud shrink.
The taping mud that's used for embedding the tape, and coating the nails, has glue in it, and it shrinks.
That's why there's much less glue in topping compound, which is what's used for final coatings, to get a smooth finish.
I would do a test run of whatever material I plan to use, either pop or drywall mud, to see if adding glue when you mix it makes it shrink.