Cement Backer Board for Tile
Cement board is a product that revolutionized the tiling industry. It's literally a board of concrete (usually in 4- x 5-foot sizes). It ranges anywhere from a half inch thick for walls to 1/4 inch thick for floors.
You can lay cement board right on top of an existing subsurface to essentially
make it concrete. It resists shifting and is impervious to water.
Cement board is much better than plywood on floors and countertops where there are no sinks or water sources. It's also an acceptable subsurface for entryways.
-- Tips courtesy of HomeAdvisor.com