So the mortar joint between the bricks at the base of the firebox and the bricks which make up the hearth appears to have partially crumbled, leaving some small gaps in the joint. As you can see in the photo it is barely visible. It has been this way for a while but I'd like to get it taken care of, if only for aesthetic purposes. I was thinking of using the Rutland high tempt mortar that comes in the caulk tube. I'm worried that the joint in question being so far from the source of heat, the product may not cure properly. So which kind of mortar do I use for this job then? Regular type N mortar? Any input on the best course of action here would be much appreciated. Thanks.
