How to Lay Ceramic Tile on a Slab

Ceramic tile can transform dull, gray concrete slab into a beautiful floor that you can match with almost any design motif. While concrete is generally a good base for tile, you need to take some precautions. Since concrete slabs can shift and crack over time, you will need to install a membrane between the tile and the slab. This crack isolation membrane allows the concrete to crack a little without destroying the ceramic tile above it.

A concrete slab needs some work before it is ready for tile.
  1. Remove everything from the concrete slab before you begin. Use a broom to sweep off the slab and mop up any remaining dirt with a mop and dish detergent. Wait for the slab to dry before you continue.

  2. Place a level on the concrete slab and move it over the entire floor. Mark any low or high spots with a pencil.

  3. Mix together leveling compound and water according to the directions on the bag of compound. Apply the compound to any low areas on the floor using your trowel. Check to ensure the areas are level before the compound dries. Use a sander to lower any high areas. Wear a mask during this process, as concrete dust will get everywhere. Allow the compound to dry according to the directions on the bag, then sweep and mop the floor clean again.

  4. Mix up some thinset mortar in your bucket, adding water according to the directions on the bad of mortar. Apply the mortar to the slab, starting in the back corner of the area. Add the thinset to an area just as wide as your sheets of crack isolation membrane from one end of the slab to the other. Once the thinset is in place, use the notched side of the trowel to create ridges in the thinset. Hold the trowel at about a 45-degree angle from the floor and drag it across the thinset to create the ridges.

  5. Roll out your membrane over the thinset with the dark side of the membrane facing up. Cut the membrane with your utility knife once you reach the end of the slab. Use your hand roller, starting in the middle of the membrane, to smooth out any air bubbles. Once the membrane is in place, apply another stretch of thinset, but have this row overlap the first by about 2 inches. Continue to lay membrane and thinset until you've covered the slab. Let the thinset cure according to the directions on the bag before you continue.

  6. Measure each of the four walls of the concrete slab and mark the center points. Run a chalk line between opposing center points and snap the line, creating an "X" in the exact middle of the slab.

  7. Place the corner of a ceramic tile into one corner of the "X." Continue to place spacers and tile adjacent to the first one, continuing all the way to all four walls. If you need to cut tile closest to the wall to less than a 1/4-inch of its normal width, adjust the starting location for the tile. Remember that there is a 1/2-inch expansion gap between the last tile and the wall. Once you have made your adjustments to the layout, make new marks near the original middle points adjusted based on how you moved the tile. Pick up the tile, erase the chalk lines, and snap new chalk lines using the new marks.

  8. Mix up a batch of thinset in your bucket. Apply the thinset to one of the four quadrants created by the "X" on the floor. Start near the center of the slab and fill a 3-foot-by-3-foot area. Use the notched side of the trowel to create ridges in the thinset. Try not to cover the "X" with thinset, as you will need it to align the tile.

  9. Place the first tile in the corner of the quadrant, right against the "X" in the center of the slab. Twist the tile slightly as you put it down. The tile should not rotate, but the twisting force will help it adhere. Place spacers next to the tile and continue to add more tile adjacent to the first one. Once you have filled in the entire area, apply more thinset to the slab and continue to install tile until you have reached the walls of that quadrant.

  10. Make a mark on the tile where you need to cut it to fit the piece against the wall. Remember to account for the 1/2-inch expansion gap that will be between the edge of this piece and the wall. Slide the tile into your tile cutter with the line on the tile directly under the cutter blade. Drag the blade across the tile to score it, then press down on the handle to snap the tile in two. Apply this tile piece as you would any other tile.

  11. Complete this process for all four quadrants, then let the thinset cure for an amount of time listed on the bag.

  12. Mix the grout with water in a bucket, according to the grout manufacturer's directions. Remove all the spacers from the tile floor. Starting from the back of the slab, apply the grout to the tile with your grout float. Push the grout down into the gaps between the tiles. Once you have covered the area with grout, drag the edge of the float diagonally across the tile to remove most of the excess grout. As you go, fill the expansion joints along the wall with silicone caulk. Continue until you have grouted the entire slab.

  13. Wait about 20 minutes for the grout to cure. If your slab was large, the first grout you applied should be cured by the time you finish the entire area. Fill your bucket with water and use a damp sponge to remove the grout from the face of the ceramic tile. Wring the sponge out well, as you don't want to get water in the grout joints. Rinse the sponge often as you go to keep it clean.

  14. Wait about three days before you put furniture back in the room. You can walk on the floor during this time, but try to keep traffic to a minimum.