The best grout sealer is a penetrating sealant that soaks through the pores of the grout. This forms an impenetrable barrier against water and other potentially damaging substances that can compromise the integrity of a completed tile job. Other types of sealants form barriers on top of the grout, rather than penetrating it. They tend to become less effective with age, however, and require more reapplications than penetrating sealants. When penetrating sealers are not available, other options include water- and silicone-based sealers as well as acrylic-based sealers. Of these options, acrylic-based sealers usually are the better choice.

Grout sealer is used to prevent the porous surface of tiles and cement grout from absorbing water after the tile job has been completed. These materials naturally soak up water when exposed, which can lead to mildew growth between the joints and beneath the surface of the tiles. This type of product is not necessary for some types of epoxy-based grout, and consumers may wish to check the type of grout used during installation prior to purchasing this product. Most types of sealant require a fresh application after a set number of years, though the longevity of the product is typically dependent upon its chemical construction.

A penetrating grout sealer is the most effective at preventing stains, mildew growth, and maintaining the color of both the grout and the tiles. This type of sealer soaks through the upper porous layers of the project materials and bonds to form an impenetrable barrier. It is long lasting, requiring a new application between 10 and 15 years. It also is more effective than other types of sealant, which are designed to form a barrier that rests on top of the tiles and grout. This barrier can become chipped with age and allow moisture to seep through to the underlying surfaces. Penetrating sealer typically cannot be used over a grout which has been previously sealed with this type of barrier technology, however, because the pours of the grout have already been clogged with the previous chemical compound.

Water-based grout sealer is not a good choice for tiled areas that will be constantly exposed to water, such as showers and bathroom floors. If a penetrating sealant is not available or if the grout is to be re-sealed after several years of use, then an acrylic-based sealant is the best choice. This type of material is more durable than its water- and silicone-based counterparts, which tend not to last more than four years per application. Acrylic-based grout sealers are also removable so that a different type of sealant may later be applied, whereas silicone- and water-based products are permanent.