After reading lots of old posts here, I made a few hypertufa pots, and a few concrete leaf castings. They are OK, and curing right now.
Yesterday I started my two spheres using a recipe someone posted here somewhere.
The recipe: 4 parts Portland cement, 1 part sand, 1 part admix, and 1 part interior latex paint. The recipe called for 1/4 fibers, but I couldn't find any, so my intention was to use the fiberglass mat after the first layer. I understood a sphere will be completed in 3 layers. The mix was nice to work with it, I guess the paint made it smooth.
I'm not sure what was the problem, but in the morning one of my two spheres was full with cracks. I started misting them, and the one with cracks just started to fall apart. The other one seems to be free of cracks.
My questions are: What should I do now with the one that has no cracks? First, how long should I wait to get dry/cure before I'll put the next layer? Use the same recipe for the next 2 layers with admix paintbrush first, and using the fiberglass mat, or using something else? I'm afraid to even touch it.