How to do it
Abide by Codes
What If You Need to Expand the Hearth?
An extension to a hearth must be the same height as the original hearth or the new tile could crack. Measure the height of the existing surface and rip 2x lumber 11/4 inches thinner than that measurement. Adding two sheets of 1/2-inch cement backerboard and metal lath mortared together will bring the extension level with the original. Locate the floor joists and mark their positions on the floor. Fasten the 2x frame to the floor with screws that penetrate into the joists. Then fasten the first piece of backerboard to the frame, mortar it, embed the metal lath, and fasten the second piece of backerboard.
Ease the Edges
Adding tile to an existing hearth will invariably raise its level above the existing floor. You can install square trim as shown above or apply eased edging with coped trim. Curved molding allows for a less abrupt transition between the floor and hearth and is easier to keep clean.