I start with generic Privateer Press bases, and add some modeling sand (rough grain) to start off the texture
Since i plan on adding water effect to these bases, i left the areas that will hold the water clear of modeling sand, and later on it will be covered with fine grain sand to give texture beyond the flat plastic.
To soften a bit the rough texture of coarse grained modeling sand, add some fine sand on top, and take care not to cover all of the coarse stone.
Rinse and repeat for all bases :)
More will come after the glue is dry :)