I noticed one of the tiles above my gas fireplace had cracked and two large pieces were about to fall off, so I carefully removed them. This fireplace has not been used in several years so the cracks most likely developed/propagated due to wind or vibrations. We got a lot of wind here and now I can feel cold air coming in from behind the tile.
What type of adhesive does it look like was previously used here to attach the tiles to the metal enclosure of this gas fireplace?
After scraping off the previous dried adhesive, what type of adhesive should I use to reattach these pieces?
I see recommendations here for "thin set with an admix", "moose milk" and refractory cement", but I'm not sure which to pursue. Ideally I'd like to be able to buy a small quantity of something (rather than a large bucket) online (and avoid having to go to a store).
After the pieces have been reattached and have settled, if the cracks between the pieces are still visible and/or have air coming through, what could I use to apply into the crevice to ensure a seal? Preferably something clear or black to match the color of the tile.