Tile can be installed over tile as long as the underlying tile is sound. Before considering whether to install tile over tile, inspect the original installation for cracks, loose tiles and water damage. If the underlying tile is not stable, the tile that you place over it will buckle, crack or fall off the wall over time. A common problem facing installers of wall tiles is the wall tiles‘ shifting downward under the force of gravity before the adhesive sets. This is usually caused by not mixing your adhesive properly. Closely follow your manufacturer’s instructions to ensure proper mixing.
Prepping the Surface
1. Clean the surface of the tile that you are tiling over.
2. Sand the surface of the tile to aid the adhesion of the new tile to this surface. Use a sander with 80-grit sandpaper to rough the surface of the tile.
3. Sweep and clean the surface to remove any dust caused by the sanding.
Laying Out the Tile
4. Find the exact center of the wall. To do this, use a measuring tape to find the center of each side of the wall and draw a perpendicular line from the edge across the wall. At the intersection of this X and Y axis is your center mark.
5. At the base of the wall lay a row of loose tiles from the center mark to the end of one of the walls or installation area. Be sure to insert two spacers in each tile so that you get a proper layout. You will most likely not be able to fit the last tile between the edge of the wall and the row of tiles. This is fine; leave that one out for now.
6. Measure the distance from the last full tile to the edge of the wall or installation area. Note this distance for later.
7. Lay another row of loose tiles from the center of the wall in the opposite direction.
8. Measure the distance from the last full tile to the edge of the wall or installation area.
9. Move the vertical center line to split the distance between these two measurements. For example, if the space on the left side is 8 inches and the space on the right side is 4 inches, move your line 2 inches to the left so that there are 6 inches on each side.
10. Repeat this process for the horizontal center line. However, because you are installing wall tiles you will not be able to rest these on the floor like you did for the vertical center line.
11. Place a tile at the center mark and hold it with your hand.
12. Put you tile spacer on top of the tile and make a mark on top of the tile spacer.
13. Set the bottom of a tile at this mark and repeat the process. Place a tile spacer and make a mark.
14. Measure the distance from the last full tile to the top of the wall. Mark this distance for later use.
15. Repeat the same process toward the bottom of the wall from the center mark.
16. Split the difference between the two measurements and adjust the center line as necessary. The intersection between these two adjusted lines is your tiling center mark. This splits the wall into four quarters. You will tile these quarters one at a time originating from the center mark.
Preparing the Thinset
17. Pour half the manufacturer’s recommended amount of water into the 5-gallon bucket.
18. Empty half of the bag of thinset into the bucket.
19. With your grinder/high powered drill set at a low speed, with the mixer attached, blend the water and thinset.
20. Add the remaining water and thinset in small batches while mixing, until you have added all of the water and thinset.
21. After blending thoroughly, allow the thinset to sit for 15 minutes so that the adhesives within it can fully incorporate.
Laying the Tile
22. Scoop a portion of thinset out of your bucket with the half-inch trowel.
23. Start at your center mark and spread the thinset across the old tiles. Tilt the trowel at a 30-degree angle and spread the thinset in large half-arc strokes. The edge of the trowel should not drag along the tile below, but should press the thinset against the underlying floor.
24. Spread several square feet of thinset out. Do not cover the whole floor.
25. Place one tile at your center mark, in the corner of the quarter of the wall that you are starting with. Do not press the tile down into the thinset, but give it a gentle, even press so that it bonds to the thinset.
26. Place a tile next to that one and insert two tile spacers between them. Place the tile close enough that you do not have to shift the tile excessively in order to be flush against the spacers.
27. Continue this process of spreading small patches of thinset, setting tiles and inserting two spacers.
28. Cut tiles that will butt against the wall or other obstructions with the wet saw. Remember when measuring these spaces to account for the distance that your joint (and spacers) will occupy in the area. The joint is the area between your tiles that the grout will occupy.
29. Continue around the room, completing the quarters marked out by your center line marks.
30. When finished, allow tile to set for 48 hours, unless you used a quickset thinset, in which case refer to the manufacturer’s curing time.
Grouting the Wall
31. Mix the grout according to the manufacturer’s instructions.
32. Scoop a cup-sized portion of grout with the padded grout float.
33. Start grouting from a corner of the room that will allow you to work toward the door. This will prevent you from being trapped in the room and having to walk over the grout.
34. Spread the grout in a diagonal direction to the joint. Keep the float at a 30-degree angle and be wary of gaps in your coverage.
35. Use a wet grout sponge to wipe up any excess grout in a diagonal direction to the joint. It does not matter which diagonal direction you clean the grout off in, just do not run the sponge straight down the grout joints yet. Rinse the sponge often and make sure you adequately remove any grout on the surface of the tile.
36. Wipe the grout sponge along the joints to recess and shape the grout within the joint.
37. Allow the grout to dry according to manufacturer’s specifications.