I use Victor dental plaster and can normally do 4 casts each mix. I normally dry outside and then finish the drying in my lounge. I use Craft Smart "tacky craft glue" from spotlight, it allows you to move blocks after glueing to get them perfectly aligned. I then ink with black indian ink from Warehouse Stationary before painting with resene test pots. I'm not promoting these companies just trying to help if you are looking for good products for terrain projects.
Here is a fantasy ruin I made using Hirst Arts and his plans.The picture has some of my C3 Mod-nor draws for a reference.
Here is the unpainted guard tower, made from one mold but cast quite a few times ;-)