This is a fun and easy excavation activity that is also great for demonstrating weathering. This excavation is a little different than most as we will not be the ones digging into to this oversized excavation. We are going to place the Rain Rock Weathering Stone outside and let Mother Nature reveal what we have hidden inside.


Excavating Adventures Pro Tip: While it is not required for this excavation activity, you can use colored sand to create distinct layers. This helps to visualize the amount of material that has weathered away over time.



Larger container. A one gallon bucket works great. A five gallon bucket is an awesome option but just be aware this will make a very large weathering stone. A kitty litter bucket, large plastic mixing bowl, or even a two liter bottle with the top cut off are all perfectly workable options.


Plaster of Paris

Measuring cup

Wooden spoon or paint mixing stick


Mixing bowl or bucket to mix the plaster and sand

Items to add to the weathering stone. These items will be revealed over time as the rain washes away material. I am a huge fan of adding assorted rough stones to the excavation. Tumbled stones work as well, but they literally tumble out sometimes as the stone weathers away. The rough stones tend to hold into the excavation and really help visualize the effects of weathering. These are just suggestions and use whatever you choose. Legos, small plastic animals, marbles, coins, pretty rocks you have collected are all great options.


Need rocks, fossils, and shells for your Rain Rock Weathering Stone? Be sure to explore our Digital Dig program and earn tons of free stuff to include in this or your next excavation activity!



  1. We are going to pour our excavation in layers. We are going to do this so our excavations items are revealed over time. To begin, place a few items in the bottom of the bucket.
  2. Mix three cups of sand with one cup of plaster.
  3. Add one cup of water and mix until you have a pancake batter type consistency.
  4. Pour the mixture over the items.
  5. Tap the bucket to settle some mixture around and around the excavation items.
  6. Allow to set and firm up for about five minutes.
  7. Repeat steps 1 through 6 adding layers onto layers until your bucket is full.
  8. Sit your Rain Rock Weathering Stone in front of a fan for several days until it is completely dry.
  9. Once your excavation is dry, turn the bucket over and gently tap the sides until the excavation slides out.
  10. Place your excavation in an area where it will get directly rained or snowed on. You will want to pick an area that you can check often. We set ours by our driveway and passed it every day as we went about or normal activities.
  11. Observe any changes in the Rain Rock Weathering Stone. Be sure to check on the excavation after heavy rains and observe any changes caused by the precipitation.


Excavating Adventures Pro Tip: Once you have the Rain Rock Weathering Stone in place, take pictures daily or weekly. This is a great way to observe the effects of weathering on your excavation.


Creating and observing a Rain Rock Weathering Stone is a great way to help a student understand the concept of weathering. This is a fun activity to incorporate in lessons regarding weathering, erosion, soil, geology, and more!


Be sure to explore ExcavatingAdventures.com for hundreds of dig kits, excavation activities, scientific trivia and more!