Publicado originalmente por James:

Similarly to real life, you can't. However, you can heat it in the kiln to get back the quicklime.

Thanks, unfortunately the kiln takes too long to heat up and i don't have the bellows. At least i know how to deal with it now

Yeah, I had the same thing happen; very punishing, for sure. I was racing to get a cistern done before the first dry season. One stone short, and the combination of factors was such that by the time I got back with the stone, the mortar had already set. Given how much effort in materials and time it takes to make mortar, it really feels like one of the most punitive hits in the game to have it dry out like that and only get back the quicklime. Why bother at that point to break it down? It's way more efficient to heat a single heavy rock again for 4 quicklime than it is to cook up a single mortar.