Tile Backer or Backer Board

The reason why you install tile backer (also known as backer board) behind tile in wet areas is because it is a better substrate than drywall, wood, and practically anything else. There is really nothing new about the concept of tile backer. Tile installers for thousands of years have created a thick base of mortar upon which to lay the tile. Installing a backer board is a substitute for troweling on countless thick layers of mortar as a base.

Backer board comes in three basic forms:

Cement Board

Wonderboard is one of the most prominent examples of cement board. It is made of Portland cement and fiberglass mat. Cement board can be cut with a utility knife, but this is a difficult process because it tends to crumble easily.

Fiber Cement Board

HardiBacker is a prominent example of fiber cement board. Unlike pure cement board, the fiber almost invisibly integrated into the board, making for cleaner cuts. If you expect to apply fiber cement board in areas of high water volume (tiling a bathtub, for example), you will want to install a barrier of 4 mm plastic behind the backer board.

Glass Mat

Glass mat such as Georgia-Pacific's DensShield is, as the name implies, dense…far denser than even HardiBacker. Glass mat is waterproof, obviating the need for a plastic barrier. Unlike cement board, glass mat cannot be cut with a utility knife. The DensShield product also claims to be mold resistant.