I recently became obssessed with the grout in my light colored tile floors. It was dark and was supposed to be white which told me that it needed serious cleaning. I turned to google to find out how to clean it. I found the following (below) and tested each on a small portion. The most effective was the bleach, with the baking soda running a close second. I also mixed the peroxide and baking soda and it didn't have better results than the two I just listed. But scrubbing tiles on my hands/knees (especially with bleach) wasn't the best option for my pregnant state. My husband rented a buffer from home depot and cleaned the tile with bleach, baking soda and some cleaning solution. the results are awesome! Only thing is after the floor is dry, the baking soda needed to be swept out of the grout. The whole process took him 4 hours (kitchen, dining and 2 bathrooms).
Cleaning Grout (from google)
My husband is a ceramic tile setter. He says the best thing to clean your grout with is vinegar. Just put it on, scrub than rinse with water. It will clean better than any household cleaner. It's very cheap. As a added bonus; it isn't toxic.
I have a large home with 5 bathrooms, all have ceramic tiles, most with white grout. A 12 year old boy gave me the tip I needed to keep the grout in great shape and EASILY as well as CHEAPLY. Hydrogen Peroxide. Spray it on, mop it on, sponge it on. It works. If there is a build up it must be cleaned first, then use the peroxide. Do not wax, as this will cause grout in floor tiles to look dirty. I apply the peroXide, leave it 10 minutes or so, then wipe off excess. disinfects too. DO NOT use with bleach. if you have stubborn stains, make a paste of peroxide and baking soda and rub. WORD OF CAUTION - peroxide wll discolor fabrics, be careful.
Fill an empty spray bottle with bleach and water (1 part bleach and 1 part water). Just before retiring in the evening, after everyone is through using the room, quickly spray the grout with this misture. The mold will disappear within 1 - 2 weeks. To keep the mold from returning, spray the grout with this solution 1 - 2 times per week. Also, make sure that your bathroom has adequate ventillation. Install an exhaust fan if you do not have one. Also, check the exhaust fan ducts to make sure that they are not clogged.
I just discovered this one myself, so I'm happy to pass on a frugal, relatively simple way to clean the grout between ceramic tiles. Baking soda! I dampen the area Gust wipe it with a damp c1oth--nothing too tricky) and sprinkle baking soda over the grout. I let it set a few minutes and then use an old toothbrush to scrub it. It really takes minimal elbow grease and absolutely amazed me the first time I tried it. I keep baking soda in an old spice shaker and use it to clean my sinks as well.