Whether it's floor tile or wall tile and it's dirty with grease, soap scum, mold, or just plain dirt, cleaning grout requires two things: a grout brush and an suitable cleaner. A grout brush is a small, stiff-bristle nylon brush, available in handheld and long-handled sizes. You can substitute a toothbrush in a pinch, but its bristles are too soft to do much good. As for the cleaner, a lot of formulas work, so you can try different options to find the best performer for your tile.
One traditional way to clean grout lines is using household chlorine bleach. For full-strength application, you simply dip the brush to a small container of bleach, scrub the grout thoroughly, then rinse with water. Chlorine bleach is strong stuff, and grout brushes tend to splatter, so be sure to wear safety glasses and old clothes. Also open the windows so that the area is well ventilated. Bleach is toxic, releases noxious fumes, and can change the shade of colored grout lines over time. Given these drawbacks, chlorine bleach is best as a last-resort solution for localized stains, rather than an everyday cleaning product.
Unlike chlorine bleach, oxygen bleach is non-toxic and safe for the environment, and it doesn’t have a harsh chemical odor. It also doesn't stain colored grout lines. Hydrogen peroxide is a form of oxygen bleach; however, it is typically sold in diluted solutions, making it a relatively ineffective cleanser.
Oxygen bleach is sold in powder form that can be mixed with water to create a paste that you apply to grout directly. Let is sit 5–10 minutes, then scrub with a grout brush. Rinse with water and wipe the floor clean with a cloth.
The Tile Council of America (TCA) recommends alkaline cleaners for removing stains from grout.
Alkaline cleaners include Spic n' Span, Super Washing Soda, and Mr. Clean, among many others. These cleaners are particularly good for cleaning dirty, greasy grout joints in the kitchen. Rinse the solution well and remove it with a rag, mop, or shop vac to get the white cleaner out of the grout.
Why Not Vinegar or Baking Soda?
Alkaline cleaners are recommended because grout contains cement and can be dissolved by acidic cleaners, including vinegar. Don't use vinegar or acid-based commercial cleaners on grout, period. Vinegar and other acids are also a no-no for stone tile because the acid can etch the stone. Another widely praised household cleaner, baking soda, is alkaline (not acid), but it has very little effect as a cleanser on dirty grout. That said, there's no harm in using baking soda if it seems to work for you.
Sealing Your Grout Lines
Cleaning grout lines can be a difficult and physical process. Once you have the grout looking clean and stain-free, sealing the grout will create a protective surface over it that helps prevent staining and makes the grout much easier to keep clean. It's important to follow the manufacturer's instructions carefully when applying grout sealer. The tile must be clean and completely dry, and you must let the sealer cure fully before using the tiled area.