Tile and stone sealers can be very beneficial for making tile, stone and grout more stain resistant, less likely to collect dirt, more resistant to efflorescence, and easier to clean and to keep clean. But sealers do not make those materials waterproof or stain-proof.
When something is spilled on a kitchen counter or floor, for example, and it’s not cleaned up right away or it’s cleaned up with the wrong type of solvent, then sealers won’t prevent those contaminates from seeping into the grout, tile or stone.
Also, sealers don’t last forever and occasionally need to be re-applied. Factors that affect the life and performance of a sealer include application location (interior or exterior) and constant exposure to things like weather, moisture or traffic conditions.
Rule of thumb: as long as water beads up on the grout, tile or stone surface and it doesn’t leave a dark damp spot, then the sealer is working. Otherwise it’s time to re-apply.