To find out if your tile is sealed or unsealed, do the following test:
Take a teaspoon of clean water and dribble it on the grout. If it sinks into the grout, you’re dealing with unsealed grout. If it beads up, it's sealed.
Step2
Once you determine that you have unsealed grout, use a dry duster or swiffer to clean out the dust. Do not pour water or other liquids onto the grout to clean it, but use a damp mop once the dust and dirt has been wiped out. Don't walk on the floor while damp!
Step3
The best way to clean cement based grout is with a Neutral pH cleaner or a steam machine. NOTE: steam can also bleach a grout's color, so purchase a neutral cleaner first (and heavy duty if the neutral doesn't clean it).
Step4
If that doesn't work, and you need something stronger, then a grout colorant stain will be needed. This method can give your grout many years of beauty and will be easy to maintain.
Tips & Warnings
Sealed tile grout is much easier to keep clean!
Unsealed grout should be cleaned frequently.
The longer the stain is in the grout, the harder it will be to clean it.
Follow the instructions carefully when using a cleaning solvent.
If you do not want to tackle the job, there are many professional companies that will perform the task for you. Look on the internet or in your phone book!