Hi, guys, just moved into a new (to me) house and have been slowly getting around fixing things, amongst the unpacking (ugh).
Here's a problem: there are two holes next to the fireplace:

The largest one is about 1/2" wide, couple of inches long. Inside, the best I can see, there's some brick + crumbling mortar. I'd like to seal and paint these holes - doesn't have to be pretty, but don't want to half-ass it.
I tried searching online, but most people's issues are with gaps between mantle and drywall. The question is, what should I use to fill the holes? Polyurethane foam? Fire-resistant caulk? I don't even know how hot the fireplace gets. Can someone point me to a product, please?
Here's a problem: there are two holes next to the fireplace:

The largest one is about 1/2" wide, couple of inches long. Inside, the best I can see, there's some brick + crumbling mortar. I'd like to seal and paint these holes - doesn't have to be pretty, but don't want to half-ass it.
I tried searching online, but most people's issues are with gaps between mantle and drywall. The question is, what should I use to fill the holes? Polyurethane foam? Fire-resistant caulk? I don't even know how hot the fireplace gets. Can someone point me to a product, please?