A mold like this will require a dense, strong mix that can also be fluid without requiring adding too much water. That’s why I used RapidSet’s CementAll.
I wanted a white base to start with and since the goal of the project was to dye it with a fabric dye so I went with Glass Block Mortar Mix.
Quikrete’s Fast Set Concrete Mix and RapidSet’s Concrete Mix, both with larger gravel- are great products for this.
I didn’t want to work with a mix that was going to have a quick setting time, since these stepping stones were so large. So I used Quikrete’s Sand Topping Mix.