Trying to make sandstone, I researched some material and the stone look I wanted was a long rectangular, stacked stone. I used this foam:
...found in the insulation section. Very cheap and the right size (as I unrolled it, I just cut in fairly similar lengths). This is something I may have changed. In the end, the monster mud that covers this did NOT stick will. So if you rubbed, scraped, or poked the foam 'bricks' the wrong way, the monster mud just flaked right off (after it was painted as well). I'm not sure what I could do different. Probably different material... if I had time, maybe thick cardboard, or something similar. Not this porous foam though. The sheets of foam were too ridged. The reason I selected this blue foam was because, of course, the well is round and I needed a material that could easily conform to that - the typical foam just didn't have enough 'give'.
Onward.
Once the well was coated, while it was still wet, I stuck the blue foam to it. While it was still wet, I covered the pieces with more mud. Filling in cracks, crevices, etc was a bit messy and some of the 'bricks' were sliding around, but was pretty easy.
This was something I may have changed as well - the spacing of the stones. Probably would have made them closer together, but that's just persona preference.
Unfortunately, these are all the photos I have RIGHT now.
Next steps:
Painting. This was tough for me. I was never happy with any colors I was coming out to. I tried LOTS of different kinds and ended settling on some reds/tans that were darked than the 'grout'. The paint covered any of the blue foam showing that I missed. However, if bumped into wrong, it was chipping.
I'll post pictures soon. That's all personal preference anyway. I painted while the mud was still wet. It blended nicely.
Also, I added styrofoam 'caps' to the top. Basically, I cut the 2 in foam into pie pieces and put them top. Secured with the rest of the monster mud, but it didn't dry in time so they were shifting all over during transportation. I'll be going back and using Liquid Nails to make sure they're secure. Again, painted similar colors. The cap was slightly bigger than the well itself so the edges hung out over the wall a couple inches.
For detail I started adding mold to the sides (it's a well right?). It didn't come out that well because I just ran out of time, but the method was to get some color green I liked and blot it on the top of the well under the cap and used a spray bottle to let it drip down the stones. It found its own path down and looked pretty realistic. Again... all personal preference.
That's about it. Or at least the basic jist of it. I stayed up till 4am on Friday night to have it finished by 9am that Saturday. I hate rushing things, so of course it could have been better, BUT I go t a lot of compliments and everyone was really impressed, so I guess, missioned accomplished. For the play, some props were added for effect - an old jug, ropes, vines around the bottom.