Did you have a typo or are you working with something called hyperfuffa? If it's a typo and you're working with hypertufa, why do you want to unmold in a couple of hours?

Spelling aside, it will be good to see something of a complete project at the end of the workshop. In other projects i have mixed Portland cement and plaster to good result but this has been in indoor applications and with tighter (less porous) aggregates.

Never tried plaster in mix. How long will students need to wait inorder to get a safe pot to take home.
I have taught a few 2 day classes and only when I really need them not to take home a project that is too fragile. .
Most of my 1 day hypertufa classes are only 1 1/2 hrs. They make the hypertufa, put in mold, and they take home a damp hypertufa mix. The mold is a low bowl, I cover with plastic so sides dont collapse. It works ok for the students and not had any problems. To help the demonstrate what to do the next day - I have a pot that I have made the day before. I demonstrate how to remove from mold and rough up with wire brush.
Below is a article that a garden writer in the area did on me, It has a nice photo of how I demo using the wire brush on the day old pot.
I like your idea and will give it a try!

This post was edited by plantman56 on Tue, Jul 30, 13 at 8:31

So you're trying to force the cure time so you can unmold the piece before the people leave? Why? I teach classes all the time. I give the class a handout, a mold and all the hypertufa ingredients. I mix the ingredients and talk them through making their planter and tell them about different methods to decorate their planters. When they're done I have a sample planter that I've made the day before to show them how to unmold and how to clean it up. Then we put everyone's name in a pot and the winner takes that sample planter home. Depending on the size of the planter the classes only run 1 1/2 to 2 hours. The handout has my phone number on it in case anyone has a problem. I've never had a phone call with a problem. Years ago I took a couple of classes. One of the classes had us bring a 18" square of plywood for a bottomless mold. You should have seen people trying to fit that into their cars.

Forgot to mention, I also giving them rubber gloves and dust masks when they take a class.
Mike, Why did you take out the link? That's a nice article.