Mosaic tiles are very small tiles (often around one square inch), which are sold pre-mounted on mesh-backed sheets of two square feet or more for easy installation. Like any other tile, they need to be installed over a hard flat surface to prevent cracking. Among the possible underlayments is a ceramic tile floor, which can provide the same solid stability as cement board, if the floor is in good shape. Make sure the ceramic tiles are very flat, don't have a high-glazed finish (the mortar won't stick) and aren't coming loose anywhere.
Things You'll Need
Belt sander with 60-grit sandpaper
Trisodium phosphate (TSP)
Mosaic tiles, mounted on mesh-backed sheets
Hand-held tile cutter
Use your belt sander to scuff the surface of the ceramic tile. Go over the entire floor, taking off any shine or gloss.
Put on your rubber gloves. Mix your TSP with warm water in a bucket according to the instructions (generally 1/2 cup of TSP powder per gallon). Thoroughly scrub the sanded tiles.
Rinse-mop the tiles with clean water. Let them dry completely.
Use your chalk snapline to lay two intersecting, wall-to-wall lines across the floor, dividing the floor into four squares. With your notched trowel, spread a few feet of mortar directly on the ceramic tiles in the corner of one of the sections where it intersects with the others. Press your first sheet of mosaic tiles into place in the mortar, in the corner between the two perpendicular lines.
Spread more mortar and lay the rest of the sheets of mosaic, using the lines as guides and working your way toward the walls. At the walls, cut away parts of the tile sheets as needed to make the mosaics fit by running your razor knife over the mesh backing between the tiles. If you have to cut tiles to fit, use your hand-held tile cutter. Let the tiles set overnight.
Apply your grout over the floor with your grout float, starting in one corner and working your way across. Scrape the rubber float across the mosaics, pressing the grout down into the spaces between the tiles. Follow up by wiping down the floor with a damp sponge to take up the excess grout. Let the grout set at least 48 hours before using the floor.
Ventilate the room when using the TSP on the floor.