Grout is a necessary material any time you install any sort of porcelain or stone tile. It is also necessary when you need to install natural rock onto a floor or into a wall. However, grout can get very dirty, very fast. There is a lot that settles into grout, and some of it is very difficult to clean. All of the following gets stuck in grout, but there is a method to get each kind of "dirt" out.
Mud is the most common of dirt to fill in the tiny holes in grout. While a mop can clean the tiles or stones, it cannot reach into the grout to remove the dirt. For that, you need an old toothbrush or a floor scrubbing brush. It is a "hands and knees" sort of job, because you have to push the bristles of these brushes down into the grout and really use some elbow grease to clean them. Warm, soapy water and maybe a disinfectant and deodorizer is your cleaning substance of choice for removing mud from grout.
Mold frequently builds and collects in shower and bath tile, as well as in entryways. Luckily, grout "dirt" of this sort is very easy to clean. Bleach and an old toothbrush to work the bleach into the pores of the grout is very effective. You can also purchase bleach "pens" that have bristled tips and are filled with a cream bleach cleaner. Regardless of what you use to scrub in the bleach, make sure you use a damp towel or rag to wipe away bleach residue. Then let it all air dry.
Pet urine leaves grout a little yellowed. It also causes a semi-permanent urine odor. You cannot use bleach on these stains because bleach and ammonia from urine create a chemical weapon known as "agent orange." Ergo, you will need to use a steam cleaner designed for grout cleaning. The steam releases the urine from the pores of the grout. A quick wipe with a damp rag and a little antimicrobial cleaner will remove the pet urine. It also kills the odors too.
Dust fills the cracks of grout quickly, especially when the tiles or stone flooring/walls are in constant direct sunlight. A dust mop used daily is effective for reducing buildup of dust in the grout. A steam mop or handheld steam cleaner and a dry rag can help with a deeper cleaning.
For more information, contact local professionals like those found at Arnold's Advanced Carpet Cleaning.