How to Set Ceramic Tile on an Uneven Shower Wall
- 1). Using your level or straightedge, determine how badly the wall is deformed. This can be done by placing the straightedge in different directions and determining where the unevenness occurs. Most of the time these humps and bumps will only be within a quarter inch, although they can sometimes be as large as a half inch -- though this is rare.
- 2). Using your margin trowel, apply five spots of mastic on the back of the tile. This is done by placing a dot in each corner of the tile as well as one in the center. This is a traditional method called "five spotting", and is used to counter uneven wall surfaces. If you are dealing with quarter-inch humps and bumps, each spot should be roughly the size of a chicken's egg. If your wall humps are larger, increase the size of the spots.
- 3). Loosely place the tile against the wall. Apply only enough pressure for the mastic to keep the tile in place.
- 4). Repeat Step 3 until you have a reasonably large area, roughly four feet by four feet, covered. Use spacers according to the size of the grout joints you want.
- 5). Place your level against the wall. The object is to create a plumb surface, meaning the bubbles on your level are between the two lines. Using your rubber mallet, softly tap each tile in the center several times, to ensure that the five spots of glue on the back are evenly distributed. Move your level around in several different directions as you work, making sure you keep the wall plumb. Avoid hitting the tiles too hard or you run the risk of pushing one in too far and throwing it all out of plumb.
Source...