Sealing tile creates a protective barrier to dirt and stains and helps keep the surface cleaner over time. Depending on the type of tile you choose, it may or may not require sealing. Generally speaking, porcelain and glazed ceramic tile does not need to be sealed. Unglazed ceramic tile, however, must be sealed to protect the porous material against stains from dirt and other materials.
Tile made of natural stone, such as slate, limestone, or marble, should also be sealed. These natural materials are quite porous and will stain if left unprotected. Be sure that any natural or unglazed tile is sealed before grout is applied. This will prevent the grout from staining the tile during the application process.
If you aren’t sure of the type of tile you have, a simple way to determine if the tile would benefit from being sealed is to test it with water. Spill a couple of tablespoons of water on a small portion of the tile’s surface. After about five minutes, wipe it dry. If the area is slightly darker than the rest of the tile (this shading is temporary) and it is in a room where spills are likely, such as a kitchen, then it is porous enough to justify sealing.