Tiles made of natural stone, such as granite, marble and slate, can create durable and resilient installations for walls, floors and other construction applications. However, these tiles feature a number of differences when compared to finished ceramic or glass tiles and these differences must be addressed during installation. One important difference is that the natural stone tiles are unfinished, meaning that they feature porous surfaces that stain easily. Applying grout to these tiles as you would to finished tiles can result in grout stains across the stone tiles. Seal the tiles and then apply grout for proper sealing without staining.
Apply a natural stone sealer to your stone tiles. Spray the sealer onto the surface or wipe it onto the stones with a soft cloth. You can find sealers at stone manufacturers.
Allow the sealant to dry overnight or follow product instructions regarding drying time for the sealant. The sealant must be completely dried before you can apply grout, to prevent staining.
Inspect the joints of your natural stone tiles. Use a flat-edged razor blade to remove excess tile adhesive from the joints, so that the grout can effectively seal the joints.
Mix stone grout and water in a clean container per product instructions; different brands of grout will require different amounts of water. Mix only enough grout to last you for 30 minutes of work. Mixed grout that sits out longer than 30 minutes will begin to set and harden before you have the chance to use it.
Fill a rubber grout float with grout. Hold the float at a 45-degree angle and scrape the flat edge across the tiles, working in a 2- to 3-foot space at one time. The angle will force the grout into the joints.
Scrape a clean edge of the float or a moist sponge across the tile surfaces to remove excess grout while it is still wet. Working in small segments will ensure that you clean away excess grout before it hardens. If necessary, use a putty knife or the edge of your finger to flatten the grout in the joints.
Grout all joints in your natural stone tile installation. Allow the grout to dry for 24 hours (or longer, depending on your product instructions) and wipe the tiles with a clean, dry cloth to remove any hardened dust particles.