Walls often are not very flat. Flexible drywall can be installed over bowed and twisted studs; once it is covered with paint or wallpaper, most people will never notice. But if you try to install tile on an irregular wall, the underlying problem will be magnified. It is very difficult to correct carpentry errors with tile. So check the walls carefully—and make necessary corrections— before you begin tiling.
Tools: Level, straightedge, and tiling and grouting tools.
1. Assess the walls. Use a carpenter’s level to check walls for plumb. Set a long level or straightedge against the wall at various points to determine if the wall is flat. An out-of-plumb wall can be tiled, but it may affect the appearance of adjoining surfaces. If the wall is not reasonably flat, repair it first.
Wall Substrates - Tile can be installed over most existing wall surfaces as long as the wall is flat and in sound condition.
Drywall - The most common wall surface, and a good substrate for tile in dry locations. Can also be used in moderately wet areas if you brush on liquid waterproofing before tiling. Repair holes or cracks with patching compound. Remove wall paper and loose paint. Lightly sand painted surfaces. Perhaps add a second layer of drywall for added strength or to cover damaged areas.
Moisture-Resistant Drywall - Commonly known as greenboard or blueboard, it is similar to standard drywall, but is water-resistant—though not waterproof. It can be used in fairly wet areas, but should receive the same waterproofing installation as regular drywall.
Backerboard - An ideal substrate for tile, especially as part of a waterproof installation on shower walls or bathtub surrounds. When installing backerboard over an existing wall surface, use corrosion-resistant nails or screws that are long enough to penetrate the wall studs.
Wall Paneling - Most sheet paneling is too thin and fragile to be used as a substrate for tile. Remove the paneling and cover the wall with backerboard or drywall before tiling.
Plaster - Install tile over plaster that is hard, flat, and in good condition. If the plaster crumbles when you poke it with a knife, it is too weak and should be replaced with backerboard or drywall. Repair cracks and indentations.
Ceramic Tile - You can tile directly over a previously tiled surface as long as it is in good condition. Remove loose or broken tile and fill the cavity with mortar. Aggressively sand the surface to remove the glaze.
2. Establish a center line and lay out. On a large wall, it is usually best to start the layout with a vertical line somewhere near the middle. If a single obstruction, such as a wall or a window, is reasonably centered in the room, then draw a line through its center. With two obstructions, make your center line at the middle of the distance between their inside edges. If you have a single offset obstruction, divide the unobstructed portion of the wall in half. Then add a horizontal line to divide the wall into four quadrants. Add reference lines to separate the field tiles from any trim tiles. Use a carpenter’s level to establish vertical and horizontal reference lines. On a wall that is less than 8 feet wide, you may want to make sure that the cut tiles on either side are close to the same size. The only way to ensure this is to make a complete dry run of one horizontal course.
Extending Electrical boxes - When tiling around electrical outlets and switches, remove the cover plates and set tile right up to the cutout in the wall. This may mean that you will have to move the electrical box forward, so that it will be flush with the finished tile surface. Extension rings are available at electrical supply outlets; mount them on the existing boxes. Before you begin tiling, make sure that you can find extension rings in the size you need, or talk to an electrician about other options.
3. Hold the files. Gravity works against you when installing wall tiles. Wall tile adhesive usually is sticky enough to prevent tiles from falling off, and most wall tiles are self-spaced so they will not slide down. In a more difficult installation, you may have to use spacers to keep the tiles from slipping, and masking tape to hold them on the wall. On each column of tiles, affix tape that is taut and well-adhered to the wall tile while the adhesive cures.