Although a tile wall doesn't need to support the weight that a tile floor does, the underlayment still must be flat, solid and secured well to the framing.
If your existing walls are flat and in good condition you can usually tile over them.
If plaster walls have holes and cracks they can be patched with spackling or joint compound. If the plaster crumbles when poked with a screwdriver it should be removed and replaced.
Loose paint should be scraped off and glossy paint roughed up with sand paper. Wallpaper should be scraped off and all the glue removed before tiling. Always make sure the surface is clean, dry and dust free before installing tile over it.
If your existing wall is damaged beyond repair, it must be removed and replaced with either drywall, moisture resistant drywall, or backerboard. Which you choose depends on your situation.
WARNING: Some older patching compounds, textured paint and insulation may contain asbestos fibers. Some paints may contain lead. Before sanding, scraping or tearing into walls, have a trained inspector determine if asbestos or lead is present.
Drywall is a standard wall covering in most residential construction. It is considered a good underlayment for wall tile as long it won't be exposed to moisture.
Moisture-resistant drywall, or "greenboard" as it's often called, is made out of the same gypsum core as drywall but with a moisture-resistant facing.
Modern greenboard may also have been treated to make it resistant to mold.
We prefer not to use greenboard in situations where it might be exposed to a significant amount of moisture (such as tub or shower surrounds). We tend to use it only in damp situations where we would otherwise use drywall. Around tubs and showers we always use backboard.
The same types of backerboard used for floors (concrete and fiber cement) can be used as underlayment for wall tiles. Concrete backerboard cannot be painted, so make sure it is completely hidden by the tile. Some of the other backerboard products can be finished like drywall if they aren’t completely covered with tile.
(See the floor underlayment section for tips on cutting these products.)
Some backer board is a bit thinner than drywall. If your backer board meets a drywall surface, you may have to first fur out the studs with strips of builders' felt as furring to make the surfaces flush.
In a bath or shower the flange at the top edge of the tub or shower base might push the bottom of the backerboard out from the studs. Use strips of builders’ felt as furring to bring the entire surface of the stud even with the surface of the flange.
You also want all the stud faces to form an even plane. (Backerboard will not bend to follow variations in the studs.) Use furring to compensate for any studs that might not be flush.
Start installing backerboard at the furthest back wall and work your way from the bottom up.
TIP: Put a blanket down in the bathtub before you work to protect it from getting scratched or chipped.
Use galvanized nails or screws to secure the backerboard. If you're working above a shower pan, be sure to nail or screw above it so you don't puncture the fabric.
The ends of the backerboard sheets should be centered over the studs, but stagger the joints so they don't line up with one another. Leave about 1/8" space between the sheets of backerboard.
Cut holes in the backerboard for around shower and bath controls. Score the mesh on both sides of the board and hammer on it until it breaks out.
You want to mud and tape the joints of the backerboard. First use a self-adhering fiberglass tape, then fill the joints with thinset mortar using a taping knife.