Is it safe to drill a one inch deep hole for a small screw and anchor into the mortar area around the rock in my fireplace to hang something? Is there any risk to piercing the inner part and letting any smoke or gases out?
I tried drill into the rock itself with a masonry bit, but I don’t have a hammer drill and it was not happening. I am sure I could get into the dried concrete, but wasn’t sure if that was safe.
Yes - for the 1" your are describing. Normally behind that rock façade is a metal mesh, some type of backboard, the 2x4 framing, etc. So a 1" hole is not close to hitting the chimmy flute.
Those rocks are pretty thick so a 1" deep hole won't be a problem. If it helps you sleep at night, squirt a little epoxy or clear caulk in the hole along with the anchor to seal the mortar.
Yes, if the chimney is made completely of rock and mortar than it is thicker than 1". If it is a facade, then there is framing and likely an air space behind the rock and the flue several inches away. If you have any doubts, just drill a little bit and look into the hole to verify that you haven't gone through
