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Build a platform with drop-in bathtub
Build a platform with drop-in bathtub
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Difficulty:
Close DifficultyBeginner Do-It-Yourselfer - EasyIntermediate Do-It-Yourselfer - ModerateExperienced Do-It-Yourselfer - DifficultProfessional - Expert
A bathtub built into a custom-made platform will add class and luxury to your bathroom. Placed in the corner of the room, along a wall or even as a centre island, it’s perfect for those who like to take a long soak!
The following project provides all the instructions you need to design and build the platform surround, to insert the tub, and to connect up the plumbing and faucets. This is nevertheless a challenging project, which requires a certain amount of experience in carpentry and plumbing. You will need someone to help you handle the bathtub as it is heavy and cumbersome.
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Tools and materials required
TOOLS
- Table saw
- Adjustable wrench
- Pipe wrench
- Pipe cutter
- Pencil
- Drywall knife
- Square
- 3/16 bit
- Spirit level
- Power drill
- Pliers
- Plier wrench
- Measuring tape
- Circular saw
- Hole saw
- Hacksaw
- Jigsaw
- Screwdriver
MATERIALS
- Bathtub
- Template
- Faucet
- 10 lengths of 2" × 3" × 96" (or 2" × 4" or 2" × 6")
- 2 sheets of plywood (or more depending on platform size and number of visible sides)
- Wood blocks - 2" × 2" × 3"
- Wood shims
- Silicone caulk
- Rags
- Glue for ABS pipes
- Bath-drain connection set with appropriate ABS pipes
- Mortar
- Caulking gun
- PEX (cross-linked polyethylene) tubing with appropriate couplings and connectors
- 2 ½" and 1 ½" no. 8 screws
Before Assembly
This project does not cover related topics on how to enlarge the surface of a bathtub platform, build a toe-kick, build an alcove bathtub platform or design a bathtub platform with a step.
BEFORE YOU START
Check that the floor is level and solid. It must be strong enough to support 50 lbs/ft² (245 kg/m²).
Read the bathtub specifications before building the platform.
Keep the template printed on the tub’s packaging as a guide to cut the plywood for the top of the platform.
If remodelling an existing bathroom, remove the wall covering in the areas that will be covered by the new platform (if applicable).
HANDLING THE BATHTUB
Choose a bathtub that will fit easily through your bathroom doorway.
After removing the packaging, inspect the tub thoroughly to ensure it is in perfect condition (no nicks or scratches).
Leave the plastic film in place around the tub to protect it during installation. Lay some pieces of cardboard (without any staples or metal fasteners) in the bottom of the tub to protect it.
If creating a brand new bathroom, take the bathtub into the room before building the walls.
PLATFORM STRUCTURE
The rim of the platform on the side where you enter the bath should be no more than 3" – 4" wide. If it is any wider it may be difficult for children or elderly people to step in and out of the bath, for parents to wash young children in the bath, or to reach the inside of the tub for cleaning.
The base of the tub must rest on the floor; the tub must never be supported solely by its rim.
For whirlpool or therapeutic tubs, space must be left in the framework for a panel measuring at least 30" × 15" to allow access to the pipes and system. For regular tubs an access panel is not absolutely necessary but it is recommended as it allows quick and easy access to the plumbing if needed. Some manufacturers also require an aeration hatch.
Check that your installation complies with the applicable building codes in your area.
LEVELLING THE BATHTUB
Some bathtubs come with an integral pre-levelled support frame. If your floor is level, no adjustments will be necessary. As long as the tub is level, the water will drain properly.
The rims of the tub must be level. The tub must be level both lengthwise and widthwise. Check using the spirit level.
Wood shims are generally used to level standard bathtubs, whether or not the tub has a support frame. Tubs without a support frame can also be levelled with a mortar bed.
PRELIMINARY PLUMBING
Remodelling project without moving existing pipework:
Choose a bathtub with a waste pipe that is positioned for easy connection to the existing plumbing. Measure carefully, as the waste pipes from the tub must fit into the floor drain.
To connect the water supply lines, PEX (cross-linked polyethylene) tubing is flexible and easy to work with, but first check that you will be able to run the piping to the planned faucet location.
New installation:
If there is no existing pipework, you can plan the position of the floor drain according to your chosen type of bathtub. Be sure to measure accurately!
The drain hole in the floor should be approximately 6” wide x 12” long so as to insert the ABS waste pipes from the bathtub. Before cutting the hole, check there are no joists, wires or other pipes running under the floor in that location.
For this project, we are assuming that the water supply lines and floor drain are already installed. Block the floor drain opening with a rag to keep debris out.
FAUCETS
Position the faucets so they are easy to reach from outside the bathtub (e.g. for running a child’s bath) and especially so they do not get in the way when entering the tub.
A faucet with shower attachment is a must for cleaning and rinsing the tub.
Use the recommended size of pipes for the bathtub faucets (½" interior diameter). These pipes are wider than those used with washbasin faucets and therefore provide a higher flow rate.
Ensure the bathtub has a wide-enough rim to accommodate the faucets. If the faucets are on the platform casing rather than the tub, make sure the spout is long enough to reach over the tub.
ELECTRICITY
If you are fitting lighting around the platform edge or installing a whirlpool or therapeutic tub, you will need electricity. All electrical connections must be made by a qualified electrician to ensure safety. Protect the circuit with a ground-fault circuit interrupter receptacle.
Have the plumbing and electrical (if applicable) work done by qualified professionals.
Steps
Platform structure
The side walls are made from 2" × 3" studs spaced 16" apart on centre and fastened to cross pieces. The framework is screwed together. 3/4" plywood covers the top and sides. The opening for the bathtub is ¾" smaller than the outer dimensions of the tub. The platform rim (the part that remains visible once the tub is in place) must be at least 3" wide after installation of the ¾" plywood and the surface finishing material.
The manufacturer generally provides these measurements as a guide for building the platform, but check them again yourself to prevent any errors and ensure a problem-free installation.
1.1. Cut the studs and cross pieces per your measurements.
1.2. First assemble the two longest sides with the studs and cross pieces. Space the studs 16" apart, centre to centre.
1.3. Next assemble the two shortest sides in the same way.
1.4. Screw the four sides together to form the platform structure.
1.5. Lower the bathtub into the frame thus assembled.
1.6. Check that the base of the tub rests on the floor and that the tub fits the frame properly. The lip of the tub should "hover” above the platform by about 1", since the plywood and finished surface are yet to be installed.
1.7. Remove the tub from the platform and make any necessary adjustments.
2.1. If one or more of the platform sides are to be against the wall, draw a horizontal line along the wall(s) in question to mark the finished height of the platform (i.e. with its plywood and finished surface).
2.2. Using a drywall knife, remove the existing wall covering below this line to expose the bare structure.
2.3. Place the framework against the wall(s) and check that it is perfectly level.
2.4. Screw to the floor and to the wall studs.
3.1. Take the dimensions of your platform frame, measuring from its outside edges.
3.2. Add ¾" for every side that will be covered with plywood. This extra width covers the thickness of the plywood (¾") that you will attach to the sides later.
3.3. Cut a piece of plywood to the correct dimensions.
With a template:
4.1. Cut out the template printed on the tub packaging.
4.2. Place it on the previously cut sheet of plywood.
4.3. Trace the outline of the template onto the plywood.
4.4. Drill a hole on this line large enough to insert the jigsaw blade.
4.5. Cut along the line with the jigsaw.
Without a template:
4.1. Lay the bathtub upside down on the piece of plywood.
4.2. Trace the outline of the bathtub with a pencil.
4.3. Remove the bathtub.
4.4. Trace another line ¾" inside the form traced previously.
4.5. On the inside line, drill a hole large enough to insert the jigsaw blade.
4.6. Cut along this line with the jigsaw.
4.7. Turn the plywood over (underside face-up) so that the cut-out is facing the right way.
5.1. Measure the length of PEX tubing needed to run from the water supply lines to the planned faucet location.
5.2. Cut the tubing to the required length. If in doubt, cut longer lengths than necessary – you can always shorten them later.
5.3. Connect the PEX tubing to the water supply lines.
5.4. Apply plumber's putty under the collar of the drain flange.
5.5. Place the drain flange over the bathtub drain hole and screw it into the drain pipe (shoe). Do not over-tighten or you may damage the tub.
5.6. Screw the tub overflow plate into the mounting flange on the overflow pipe.
5.7. Connect the drain tailpiece to the floor drain.
NOTE: The type of rim on your bathtub will determine whether you need to install the platform surface covering before or after fitting the tub. In this project, we will be tiling the surface after inserting the tub.
6.1. Lay the plywood cut-out on top of the platform.
6.2. Insert the bathtub to check the fit and adjustment. Take care not to damage the ABS piping protruding from the tub. It should fit into the floor drain hole without difficulty.
6.3. If no adjustments are required, screw the plywood into position.
6.4. Insert the tub’s ABS waste pipe into the floor drain. If it fits properly, glue it in place.
6.5. Level the bathtub if necessary, with the aid of shims or wedges attached to the floor. If the tub has no integral support frame, screw small blocks of wood on either side to prevent it from moving.
7.1. Calculate the centre point of the faucet.
7.2. Mark the locations of the faucets, spout and hand shower on the rim of the bathtub or platform, according to the manufacturer’s instructions and/or measurements.
7.3. Drill 3/16 " pilot holes at these marks. Check that the marks line up properly with the faucets and with the locations of the installed pipes.
7.4. Cover the marks with a piece of masking tape to protect the tub surface when drilling.
7.5. Drill the holes using a hole cutter.
7.6. Install the faucets according to the manufacturer's instructions.
7.7. Connect them to the PEX pipes. Cut the PEX tubing if it is too long. Note: if the faucets are to be installed on the platform and you are covering the platform with tiles, the tiling should be done first.
8.1. Flush the toilet a few times to get rid of any residue in the pipes.
8.2. Fill the bathtub with water (hot and cold) up to the overflow level.
8.3. Keep the tub filled for twenty minutes.
8.4. When the twenty minutes are up, check that all the plumbing connections are watertight: pipes, drain, overflow and tub.
8.5. Empty the bathtub.
8.6. Check that there is no water remaining in the tub bowl. If there is, either the bathtub is not level or something is pushing up against the base of the tub.
Plan an access panel on one of the sides to allow for easy access to the plumbing.
The access door should measure at least 30" × 15". For maximum access to all components and especially for tubs with whirlpool or other systems, you can make a panel spanning the length of the platform. Designing an access panel requires some thought.
9.1. Measure and cut a piece of plywood the same length and height as one of the platform sides.
9.2. Screw this piece to the frame.
9.3. Measure the length and height of the adjacent side and add ¾" to the length to cover the thickness of the plywood installed on the first side.
9.4. Cut another piece of plywood to these measurements.
9.5. Screw to the frame. The plywood on the top of the platform should cover the thickness of the plywood on the side walls.
10.1. Vacuum and clean all the surfaces.
10.2. Install your chosen finishing material on all sides of the platform.
10.3. Seal the joint between the tiles and the bathtub with silicone caulk, holding the caulking gun at 45o.
10.4. Smooth the caulk with your index finger or with a plastic finishing tool. Dip your finger in water or dishwashing liquid to prevent the caulk from sticking.
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