The kit is at your local hardware store, and craft stores. I just mix cement sand and crushed coral/shells equally. I don't mix to runny but rather on the dry side.
Rubber made tubes filled with wet sand for the molds. I had foundry in high school, but since you are not pouring, it takes a different approach. Just plop the mix in and pack sand around to hold the shape. I usually sprinkle with aragonite or shells or some other decorative texture prior to pushing the cheap sand against it.
I tried a variety of other methods and mixes, but this is one I like. I tried using rock salt and water softener pellets, lots of extra soaking, and that also weakens the rock.
I tried vermiculite to lighten the rock, but after some time in the tank, water would go acid. Took almost a year to settle down, and then the rock started to fall apart.
With this mix, I have higher than normal ph, but vinegar brings it back down. Much easier than bringing ph up. I did not wait any extended time like much of the other directions advise. One week and into the tank for cycling.
You can see some of my earlier works in my blog.
