If your shower has a shower pan, replacing just the pan is possible, but not always advisable. The point of having a shower pan is one part versatility and one part convenience. Shower pans are made to work with fiberglass shower surrounds and tiled walls. They fit on the floor inside the shower, and act like a tub keeping water off the floor. These pans are fairly shallow and can be removed using basic tools, as long as a few conditions are met.
Any shower pan is designed to be removable. The pan installs at the base of the shower, rising up about four inches (more or less, depending on the model) to the wall. It is installed in tile showers and fiberglass wall showers. In the latter, the bottom edge of the fiberglass wall overlaps the top edge or lip of the shower pan. Begin removal by taking off the shower surround walls to gain access to the shower pan, which fits under the shower surround walls. This is not true for tiled shower walls, however, where the pan does not fit under the tiles.
Another basic part of removing the shower pan is cutting the drain pipe. This attaches to the base of the shower pan using a special two-part drain piece, which unscrews from the shower pan. This is screwed into the shower pan during the installation process, and a ring of plumber's putty is applied. Breaking this seal takes some effort, so usually the drain and pan are removed together.
Fiberglass Shower Walls
Since the shower pan is installed before the fiberglass surround and shower walls, with the shower walls overlapping the edge of the pan, removing the pan alone requires extra work. In most cases, replacing the walls along with the pan is the best method. If you can extract the pan by prying up the bottom of the walls, you will be able to complete the job. However, one must consider the extra effort involved in this project and the potential damage to the shower walls.
Tiled Wall Showers
In a tiled shower, removing the pan is easier, since the pan is caulked into place at the bottom edge of the tiling. There is no overlapping fiberglass wall to impede the removal of the pan. Simply cut the caulking and drain pipe to remove the shower pan. Break and remove tiling around the edges of the pan if it prevents removal. A tile hammer and chisel are ideal for this task. Replacing the pan requires a simple reinstallation and caulking to create a watertight seal between the pan and tiled walls.