Why grout gets so dirty
Grout is porous. Every time you mop, dirty water runs into the grout lines and sits there. Most mops push grime around more than they pick it up, and grout is the low spot where it all settles. Kitchens and entries get it worst. Showers add soap scum and hard-water scale.
What I do
- Pre-treat grout lines with a cleaner suited to the tile and how dirty it is.
- Agitate with machine brushes and hand brushes along the lines.
- Extract and rinse so the dirt actually leaves your house instead of drying back into the grout.
- Seal the grout with a penetrating sealer once it's dry, so it stays clean longer and mopping actually works.
What about natural stone?
If your tile is travertine or marble, many grout cleaners are too harsh for it. Acidic grout cleaners will etch stone. I use products that are safe for the tile you have. For travertine floors, grout cleaning is usually part of cleaning and sealing.
Commercial restrooms and kitchens
Restaurant kitchens and commercial restrooms can get grease and urine salts deep into the grout. Regular deep cleaning is part of keeping them sanitary and keeping odors down. See restaurants.
Grout that won't come back
Sometimes grout is stained, cracked or missing. Cleaning won't fix that. Regrouting or grout color sealing might. I'll tell you what I see.
Showers
Shower tile gets hard-water scale and soap scum. Cleaning it, then sealing the grout and any stone, makes daily upkeep a lot easier.