There is no footing under the wall or the fireplace all you have to do is look back a couple pages in this thread and you can see it. It is wrong and it will crack as soon as it gets a small frost shift. You def cant build a fireplace on a 5" concrete slab and expect it to not have and cracks in the stonework..
...I know none of us on here like to be told are work is wrong,but this is not the right way to start a wall and fireplace out. You have got to be at least 36 inches in the ground with your concrete footer no questions asked.