Ceramic tile material is rigid and relatively brittle, so a sturdy base is the most critical part of installing this type of tile. Unless you want to see cracked tiles, loose tiles, or loose grout, you need to select the proper underlayment. Underlayment being what the construction trade calls the layer that goes between your wood subfloor and your tiles.
You have several alternate ways to accomplish the strong underlayment required for ceramic tile installation.
Plywood- just a single layer of plywood isn’t rigid enough to stop floor deflection. It needs to be covered over with an additional layer of exterior-grade plywood to achieve a total thickness of at least 1 1/8 inch. You can either (A)- Cover the plywood with a cement backer board (more on these below) or (B) Cover the existing plywood with a second layer of exterior grade plywood. Under either of these, a thin-set mortar is applied to eliminate air gaps. Additionally, in bathrooms, it’s recommended to lay a “shower pan” over your wood subfloor. This refers to thin rubberized materials that protect the tile from floor expansion and contraction due to moisture, temperature and...