All grout is a porous, and stains instantly and often permanently. Believe it or not, stained or dirty grout is often caused by the cleaning process. As the grout joints sit lower than the tiles, dirt and other contaminants are pushed into the grout joints during the process or scrubbing or mopping tiles.
In damp or wet areas, such as showers and bathrooms, the penetration of grime into the porous grout joints becomes a breeding ground for mould and bacteria. The solution is to have the grout sealed by a professional, who can advise of the right sealing solution for your tiles and situation. In general, local hardware sealing products are not a long term solution, and are often applied incorrectly. Before any grout sealant is applied, grout needs to be ‘prepared’, and the product must be compatible with your tiles. Applying the wrong sealer to tiles can result in costly, often irreparable damage.