Raised Tile Hearth . In front of your fireplace you have to have 18” of noncombustible material either raised or on the floor. Allow thinset to cure 24 hours before applying grout. fireplace, new construction, cultured stone, raised hearth, builtins from www.pinterest.com Using the trowel’s notched side, spread an even layer of thinset and firmly press each tile down. This rustic fireplace complemented the rustic interior and exterior of the home. In front of your fireplace you have to have 18” of noncombustible material either raised or on the floor.