First a structural framework is created using polystyrene or expanding foam. Then this is textured using the ProRep Terrascaping Texturing Compound (sold separately), before being waterproofed using ProRep Terrascaping Sealing Resin (sold separately).
This colouring pigment is mixed with the sealing resin to create a colour which matches the desired effect in the terrarium. Adding more or less of the pigment will determine how dark or light the colour is, and the pigments can be mixed to create different colours.