The Ontario Building Code | Firebrick Liners
(1) fireplace liners shall be not less than,
(a) 50 mm thick for the sides and back, and
(b) 25 mm thick for the floor.
(2) Firebrick liners shall be laid with high temperature cement mortar conforming to CAN/cgsb-10.3, "Air Setting Refractory mortar".
(3) Joints between a firebrick liner and the adjacent back-up masonry shall be offset.