Ten years ago I built a barbeque pit out of concrete blocks. I lined the inside of the fire box – the sides and bottom – with fire brick. I used stone tiles, 1/4″ x 12″x12″ for the outside face and on top for the work area, and regular grout and adhesive for outside applications. Then, about six years ago, some of the top tile cracked. I replaced them. Two years ago they cracked again, in the same place. There are no cracks in the sides anywhere so don't think settling is the issue. Maybe it's due to the heat of the firebox? I cook with wood. I am planning on replacing the cracked tile again but would like to find out why it keeps happening. Any thoughts?