I have a lp gas log black pipe thats coming through my fireplace that I intend to seal once I remove it so I can install a wood stove. I thought I was going to install fire caulking and then mortar over the hole about 2 inches deep in the hole but have recently found out that the fire caulking is only rated for 300 to 400 degrees so I am needing some advice on what to put into that hole. Mortar mix is fireproofing? right? so should I just use mortar or cement rather than the caulking or do they make something especially for this application that I am not aware of?