A major job in any comprehensive bathroom renovation is laying new tile. Something as simple as a new tile floor can completely refresh the appearance of the bathroom. Many are discouraged from attempting a bathroom tiling job because they think they need to laboriously pull out the old tile and resurface the floor substrate before starting. A useful shortcut is to lay your new tile right on top of the old tile.
Inspect the tiles before starting your work. Any cracked or loose tiles need to be removed with a pry bar. You might find it necessary to shatter the tile with a hammer to accomplish this.
Mix up some ordinary mortar in a bucket, following the directions of the manufacturer. Pour enough mortar to fill the empty spaces created by removed loose or damaged tiles, and smooth the surface out with a trowel. In the case re-tiling a wall, use tile adhesive instead of mortar. Allow this to dry overnight, but continue on to Step 3. It will not interfere with the drying mortar.
Scratch the surface of your tiles if they are of the glazed, shiny variety. Drag your notched tiling trowel across the tiles until it is thoroughly scratched up. This will provide a better surface for the mortar or tile adhesive.
Check the floor with a level, and if it is not level be prepared to make it so when you pour mortar on the floor. Sweep any dust or debris off the floor or walls.
Set your adhesive in a work area that is roughly 2 or 3 square feet, starting in a corner. Use tile adhesive for re-tiling a wall, and thin-set mortar with latex adhesive for re-tiling a floor. Spread out a thick layer using the tiling trowel, and then etch grooves into the surface by drawing the trowel's notched edge across it.
Place two tile spacers for your first tile. Follow the same pattern throughout the tiling job. For example, if you start by placing spacers on the left and top of your first tile, follow the same pattern for all successive tiles.
Lay your first tile. Place the tile on the layer of adhesive/mortar, give it a press and a twist to create a solid bond, and then twist it back into proper alignment.
Repeat Steps 2 through 4 until the entire work area is tiled. Periodically check your work with a level to make sure you are applying the right amount of adhesive/mortar. If you are working on a wall, leave the spacers on the tops and bottoms of the tiles in place, as this prevents them from sliding.
Allow the tiles to set overnight.
Mix up your grout in a bucket as directed by the manufacturer, and push it into the grooves between the tiles using a tile float. Allow this to dry overnight.
Chip off any unwanted grout encrustations with a plastic scraper, and wash away the residue with white vinegar, a scrub brush and old rags.
Laying tile over tile has the natural result of raising the level of your floor or increasing the width of your walls. Take this side effect into consideration when you plan your bathroom renovation. You may decide that you want to remove the old layer of tile after all.