Ceramic tile is a durable material that requires little maintenance. The glazed surface of the tile is both hard and resistant to staining. Grout lines between the tiles, however, are made from a more porous material that can become dirty and stained over time if it is not protected with a sealer.
Set ceramic tiles in a bed of thin-set mortar with spacers used to keep them equidistant. Once the mortar has hardened, use a rubber float to fill the joints with grout and wipe off any excess with a damp sponge.
Unless a special stain-proof grout was used on your floor when it was installed, the grout lines should be sealed after the grout has fully cured (usually 30 days or more) to prevent future staining.
Start by mixing up a mild bleach solution in a bucket to be used to clean the grout lines.
Use a small scrub brush or old toothbrush and clean the grout lines with the bleach solution.
Mop the floor and rinse with clean water to remove any bleach residue. Allow the grout to dry thoroughly before applying a clear sealer.
Clear liquid sealer can be found in the flooring department of home improvement centers. If the sealer doesn't come with a built-in applicator, purchase a separate applicator bottle and pour the sealer into it.
Apply the sealer to the grout in a smooth, even line, making sure not to miss any joints. Allow the sealer to dry thoroughly.
If you waited too long to seal your floors, and the grout lines have already become stained and will not come clean, consider using a grout stain pen. The pen contains both a sealer and stain to impart a uniform color to the grout lines while sealing the grout at the same time. Simply rub the pen on the grout lines and allow it to dry.