i was just wondering, i also wasn't quite sure how to figure out how many pounds of force would be required.
I don't know , but it is not as hard as it looks. You need stable mounts and very good technique. The stones I use are patio pavers, 2x8x16. Stack two to get your specific dimension. Concrete is quite brittle, so a good, sharp strike will crack it. Because wood flexes, I find it easier to break two patio stones, than five boards.
