Replacing a one piece shower and tub is one of the most impactful updates you can make in a bathroom, instantly modernizing the space and fixing persistent plumbing issues. This project, while intimidating to DIYers, follows a logical sequence of steps that prioritizes safety and precision. Success hinges on careful planning, the right tools, and a methodical approach to disconnecting old fixtures and installing the new unit. Before starting, it is essential to understand the scope, which involves removing the old drain, waste lines, and the fixture itself, then setting a new unit with a reinforced substrate.
Initial Planning and Safety Preparation
The initial phase of any bathroom renovation is critical, and rushing this stage leads to mistakes. You must begin by turning off the water supply to the bathroom, usually located near the fixtures or in a basement utility area. It is not enough to simply turn the handle; you need to verify that no water is flowing by attempting to drain the tub and turning on the sink faucets. Next, you must cut the power to the bathroom at the main electrical panel because you will be working with plumbing connections in close proximity to potential live wires from vanity lights or GFCI outlets.
Gathering Tools and Measuring
Having the correct tools on hand prevents mid-project trips to the hardware store and ensures a clean installation. You will need an adjustable wrench, channel-lock pliers, a reciprocating saw or hacksaw, a utility knife, a torque wrench, and a variety of screwdrivers. A helper is highly recommended, as one piece units are heavy and awkward to maneuver. Before demolition, measure the new unit to ensure it fits the existing footprint; standard widths are 60 inches, 66 inches, and 72 inches, and you must verify the rough-in dimensions for the waste pipe centerline.
Removing the Old Fixture
With the utilities off, you can begin the demolition process, which is often the messiest part of the project. Start by removing the decorative caps over the faucet handles and screws, then disconnect the water supply lines leading to the tub spout and valves. You will need to access the underside of the tub, which often requires cutting away the drywall or tile surround to expose the flange bolts. Use the reciprocating saw to cut through the old cast iron or steel drain body, allowing the unit to separate from the floor.
- Turn off water and electricity to the bathroom.
- Disconnect water supply lines and drain piping.
- Cut through the drain body and remove the old fixture.
- Clean the subfloor and remove any old sealant or debris.
- Install the new drain assembly and overflow system.
- Prepare the substrate for the new unit with cement board.
Preparing the New Drain and Subfloor
Before setting the new tub, you must prepare a solid and waterproof foundation. If the old setup used a metal drain, replace it with a modern ABS plastic drain assembly that matches the new tub's specifications. It is crucial to ensure the new drain is level and securely attached to the PVC waste line; a uneven drain leads to standing water and slow drainage. Next, inspect the subfloor for any rot or soft spots caused by past leaks, and replace any compromised plywood. You should then install a cement board substrate, sealing the seams with tape and thinset to create a moisture barrier that protects the new flooring.
Setting the New One Piece Unit
With the subfloor prepped, you can set the new tub, which requires coordination and careful lifting. Position the tub in the alcove, aligning the drain with the new waste pipe. Gently rock the unit into place, ensuring it sits flush against the wall and the adjacent surfaces. Once the position is correct, you must immediately check for levelness using a long spirit level, adjusting shims under the feet as necessary. After the tub is level, you will need to torque the mounting bolts to the manufacturer's specifications to ensure the unit remains secure and does not shift over time.
Connecting Water and Final Waterproofing
The final stages involve restoring the water supply and ensuring the fixture is completely sealed against moisture. Reconnect the hot and cold water lines to the faucet stems, using new washers or O-rings to prevent future leaks. Turn the water supply back on slowly, checking the valves and connections for any drips before the water reaches full pressure. The last step is to waterproof the curbs—the vertical edges where the tub meets the tile floor—by applying a high-quality polyurethane sealant. This bead of caulk is the last line of defense against water seeping under the unit and damaging the subfloor.
