Like many floor tiles, marble tiles require grout to prevent water damage to the floor and to stop the tiles from rubbing against one another, potentially damaging the tile. Since marble is a natural stone, it is porous and may absorb some of the grout as it is being applied. To prevent this from happening, apply a sealer to the tiles before spreading the grout. This will help release the grout, enabling you to clean up without damage to the floor.

1
Paint or roll a coat of marble sealer onto the floor tiles. Overlap the edges of each stroke, and cover each tile completely with the sealant. The marble should appear wet. If dry spots are apparent, apply sealer. Wait 10 minutes for the sealer to fill the pores of the marble and buff the tiles dry with an absorbent cotton cloth.

2
Scoop some grout onto the marble floor with a grout float or rubber grouting tool. Hold the float at an angle to the marble to push the grout across the surface of the tiles, and direct it between the joints. Push the grout from each side of the joint to ensure even coverage. Hold the float flat to the marble as you push the grout into the joint to pack it in. Pay close attention to the wide grout joints or broken corners on tumbled marble to ensure complete coverage.

3
Wet a grout sponge with rounded corners and squeeze out the excess water so the sponge is damp but not dripping. Wipe the surface of each marble tile by using one side of the sponge for one pass over the tile. Rinse and wring the sponge out after each side has collected grout. Repeat until all the grout is gone and a loose tile is held up to the finished tiles. The loose tile should resemble the floor tiles exactly, if a haze exists on the finished tiles, rinse them with clear water again.