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The type of stone, tile and grout that you have will determine if sealing is necessary. Glazed ceramic and porcelain tiles have almost no porosity and are highly resistant to staining; therefore, sealing is not required. However, it is beneficial to seal unglazed, polished porcelain floor tile. If either the tile or grout is considered porous, such as natural-stone tile, terra cotta, Saltillo, brick or cement-based grout, sealing is recommended.
The best time to apply a sealer to the grout is after the grout has cured a minimum of 24 to 72 hours, depending on the manufacturer's instructions.