Unlike the ceramic tiles it separates, grout by itself is quite porous. It easily absorbs any water and oil-based solutions that land on it. The moisture, in turn, promotes growth of mold and mildew on any organic material present.

 

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To clean grout, turn on the exhaust fan (or open the window), apply a bleaching cleanser to the grout lines and let it work for several minutes. Heed all cautions and warnings on the label. Apply the cleaner a second time while using a grout brush to scrub out all the grout lines. Rinse the tile well, and dry the surface with a towel. Keep running the fan until all is dry.

When the grout is completely dry, consider applying a masonry sealer with a fine paintbrush. Follow label instructions. Sealer is available at home centers and hardware stores. The grout won’t absorb as much moisture and grime once all the tiny pores have been sealed, making future cleanings easier.

 

 

Reference:

 

Don Aslett in The Cleaning Encyclopedia: Your A to Z Illustrated Guide to Cleaning Like the Pros.