I don't think that the heat makes for great curing. If you go to a mattress store and ask nicely they may give you old mattress bags. These are heavy plastic and large, you can put your ball or what ever in there, add water, and roll up and tape the top. I use matt bags for my work area to keep it clean also. Too bad about the flaking, a two tone finish should look good though.
Cindy

Hey Rick --- Sorry to hear about the flaking. When I "steam cure" mine I seal them as air-tight as possible and leave'em for about five days. Never had a problem. Heat is not the enemy unless moisture can escape. Then it's a beeeg problem. Nearly all the commercial concerns you hear about controlling heat is in reference to the internal heat build up that occurs when very large masses of concrete are poured at once. There are even "low heat" cements designed to offset that problem. Regular old Portland is fine up to about 290 degrees while curing, again...as long as there is sufficient moisture retained to complete hydration. These days, flat work in areas like Arizona gets a coating of a chemical compound called a "liquid membrane seal" that prevents moisture loss even though the exposed surfaces often exceed 150 degrees in the sun. No moisture loss...no problem.

One thing you do have to be very careful about when curing in a sealed bag is to make certain the work has set thoroughly before dousing it down and locking it up. Too much moisture too soon and you wind up with a weakened mixture which is indeed prone to flake. Especially when thin layers are involved. But then, thin layers are always tricky simply because there is so little mass that all the forces at work (heat, evaporation, air movement) are acting very quickly.

Good luck and do what works best for you. I never argue with success, no matter what techniques are applied.

Cheers from the Sunny (and hot & humid) South --- Tango