We make rock at school. I don't follow any of those recipes. I use Portland Cement, Oyster shells and acrylic shavings. The acrylic shavings make the rock lighter and stronger. I just eyeball the mixture til it is the consistency I like. I then do wacky stuff with it like pouring it over an inflated rubber glove. Makes for lots of caverns and caves. You can shape it all sorts of ways. The main thing is that you need to cure it for awhile after you make it. There are several ways of curing. I am patient about this so I just put it in fresh water with a powerhead and change the water at least once a week. Some people add vinegar to speed up the process but I dont. Hope this helps. I think we could possibly do a rock making workshop at my classroom some Saturday or Sunday if there is enough interest.