The first step to cleaning grout between marble and limestone tiles is to find the correct type of cleaner. Since these types of tiles are porous it is important to choose a cleaner made for them, otherwise you may etch your beautiful marble and limestone floors. Once you have found an appropriate cleaner you are ready to tackle that dirty grout.
The next step is to prepare your work area. Any surfaces that do not contain grout to be cleaned (eg hard wood floors, door jams, baseboards, carpet, etc.) need to be covered. Use some type of plastic sheeting and duct tape to cover the areas that do not contain grout. If duct tape is not ideal for the surface you are attaching to, you can use painters tape to avoid any tape residue mishaps.
It is very important to test the cleaning product on a small inconspicuous patch of grout before cleaning all of the grout. When testing the grout cleaner be sure that the grout and tile are dry. After testing the cleaner be sure to wipe the edges of any surrounding tile to check for any change in appearance or texture. If there is no change to the tile and the cleaner is suitable you may continue with the following process. If there is a change to the tile you have the option to tape the edges of the tiles with duct tape. This will protect the tiles while still allowing you to clean the grout in between them.
After you have tested the cleaner and appropriately prepared your work area you may begin tackling the dirty grout. You will want to clean your grout in sections of approximately three feet lineally. Generously apply the cleaner to the first section of grout. You will want to work the cleaner with a grout brush , due to the nature of marble and limestone, be sure to use a nonmetallic brush to avoid any damage to your tile. You will use the brush to work the cleaner for approximately 20 seconds. Next you will want to pick up the dirty solution with a mop or sponge. Be sure to rinse the grout twice with clean water after mopping up the solution. Then repeat this process for the remaining sections of grout.
If your grout is extremely dirty it may be necessary to clean it again. In rare cases the grout may not be salvageable. If this is the case the last option would be to remove the old grout and replace with new grout.
Marble and limestone offer a beautiful addition to your home or business. It is important to care for them properly and this includes the grouting between the tiles. Using a high quality grout cleaner specifically made for marble and limestone grout is highly recommended.