Well a couple of things that would seem to be an issue....firstly underground water heading toward the surface...so plants basically can't use roots to tap water...also speaking of roots...roots break stone down to soil and you can't have soil...it'll just fall away. Between these you are going to have serious issues with plants...you may be able to pull off lichen but not much more...
Also you're going to have a problem with air pressure....figuring out where the air and water "go to" becomes an issue because otherwise the air just fades away and nothing can breathe.