Pour the concrete mix into a bucket and start adding water a little at a time. Stir and keep adding water until you get a thick cake batter-like consistency.
Coat the inside of your larger bowl with oil. Coat the outside of a smaller bowl with oil as well. This helps make it easier to pop out the concrete piece once it's dry.
Time to make your bowl! Spoon concrete into the bottom of your big bowl, half full. Then place your smaller bowl into the bottom center of the big bowl and push down. Tap the bottom and sides of the big bowl to agitate the concrete, getting rid of air holes. Smooth out the rim of concrete with a spoon or your finger. The smoother you get it now, the less you'll have to sand it down once dry.
Place large rocks into the smaller bowl to weigh it down and keep it level while drying. Give the concrete 24 to 48 hours to dry. You'll see the concrete lighten in color as it dries.
Once the concrete is light grey and dry to the touch, remove the plastic bowls. Now you can sand the bowl to smooth it out.
Ready for styling!