The 1” thick ledger pieces above my inline gas fireplace keep detaching from the drywall behind them. i tried high temperature adhesive to put them back but they keep dropping from the heat. I am not sure how to approach securing these tiles, any ideas? the screen frame of the fireplace is the only thing stopping these pieces from dropping to the ground. It is smooth drywall behind these pieces. i don’t know why contractor didn’t use something else behind this.