Can this product be used to regrout an existing shower floor. Looking to change the color.

Thank you for your inquiry regarding MAPEI Products! In order to grout over grout, you must remove 2/3rd depth of the existing grout joint and then you can re grout using a sand and cement based grout or the Mapei Flexcolor CQ. Flexcolor CQ will adhere to itself, but it will not adhere to a cementitious grout joint. That being said, if your current grout joint in sound and firmly installed, you may want to use the Mapei Grout Refresh as follows:GROUT REFRESH Although Grout Refresh is applied in much the same way a traditional paint would be – it is NOT a latex paint finish. It is an acrylic-based stain (colorant) & sealer in one. It will not “erode” after several cleanings. Never use a solvent-based cleaner! Correctly applied and maintained, it will last a number of years before needing to be re-applied. Foot traffic, cleaning solutions and other variables will ultimately dictate the longevity of the product. Application can be time-consuming – especially in larger areas. TIPS: - Grout Refresh is not recommended in steam showers or saunas; - ¬¬¬¬¬¬¬¬¬¬¬The best way to apply Grout Refresh is with a small artist’s paint brush. Keep a damp sponge nearby to wipe off the excess Grout Refresh from the surface of the tile as you go. Grout Refresh can also be applied using a small piece of sponge, a foam applicator or a tooth brush. - Typically, one coat of Grout Refresh is sufficient when the existing grout is similar in color to the Grout Refresh. If you are making a dramatic color change – e.g., switching from brown to white for example – then two coats may be required. - If you get some on the tile surface, it can be removed (while still fresh) with water and a light duty scrub pad (the kind used for fine china). If the Grout Refresh has dried and is stuck on the tile, use MAPEI UltraCare Heavy-Duty Sealer and Coating Stripper. If you haven’t already done so, we recommend reading the Grout Refresh Technical Data Sheet online and following the directions carefully. Hope this helps! Thank you! Product Advisor # 11