Grout is the filler between tiles, and it's just as important to the appearance of the floor, wall or countertop as the tiles themselves. To keep it looking its best, it needs to be periodically resealed to prevent blackening from mold, grease and ground-in dirt. Although you should do this once a year, on average, the frequency depends on several factors, including the type of grout, the location of the tiles, the amount of traffic and the type of sealer you use.

Clean grout lines in bathroom.
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As a rule of thumb, you should reseal tile grout once a year to keep it looking its best.

Different Types of Grout Need Different Care

Traditional grout is a mixture of Portland cement and pigments. Tile installers use this mixture as-is when the tiles are closer together than about a quarter-inch. When the joints between tiles are larger, they add sand to the mixture. Both sanded and unsanded grout are porous; moisture can penetrate deep inside and provide nourishment for mold colonies that grow in the pores.

Epoxy grout is a recent addition to the tile setter's toolbox. Epoxy is a type of plastic, and it isn't nearly as porous as cement; therefore, mold is less likely to grow inside it. It's just as susceptible to surface grime as traditional grout, though.

All types of grout benefit from some type of sealer, and for cementitious grout, a sealer is more than a benefit -- it's a requirement. The two broad classes of sealers are those that penetrate and those that form a film on the surface. Penetrating sealers provide the best protection for porous grout, while epoxy grouts usually need only a film coating. You can also apply a film coating to cementitious grout when your intention is to change the color.

Gauging When It's Time to Reseal

Trade professionals generally recommend resealing grout at least once a year, but the truth is that you can usually wait longer, and many homeowners do. You need to keep an eye out for telltale signs of wear, though, or you may have a time-consuming cleaning job ahead of you before you reseal. Here's what to look for:

  • Film Coatings: Surface sealers are like paint; when they begin to wear, you'll see signs of cracking and chipping, and the unsealed grout will begin to appear in spots. Because the sealer and grout are often different colors, these spots should be easy to see.
  • Penetrating Sealers: When grout has a penetrating sealer, the first indication that it's time to reseal is often a darkening of the grout itself. This darkening means that dirt has penetrated the sealer and started to become lodged in the grout. As soon as you notice the color change, it's time to reseal. If you wait, it will only get worse, and you may have a more difficult time restoring the original color.

Clean the Grout Before You Reseal It

You can find a wide selection of commercial grout cleaners, or you can make your own from common household supplies. Some cleaners are stronger than others, and as a rule of thumb, it's best to use the mildest cleaner that will get the job done to avoid affecting the finish on the tiles. When cleaning a film coating, a mixture of soap, water and vinegar may do the job. On the other hand, you may need a strong cleaner containing bleach or hydrogen peroxide and a mild abrasive to both kill mold inside sanded grout and clean the surface.

Apply the Sealer According to Directions

The depends on the type of sealer you are using. Most can be applied with a V-tip foam brush, but in some cases, it's more effective to use a paintbrush or even a rag. Consult the directions on the sealer container, which will also tell you how long you must allow the sealer to cure before you can get it wet or walk on the tiles. It's typically 24 hours, but in some cases, it may be longer. The directions will also tell you what to do if you get the sealer on the tiles. In most cases, you can just wipe it off, but if the tiles are porous, you may need to remove it with a solvent, such as mineral spirits or alcohol. Don't let the sealer dry on the tiles, or you may have to scrape it off with a razor blade.