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Installing a bathtub is labor intensive yet simple. Here’s one way to do it.
Step 1 – Cut a Drain Hole
On a level subfloor cut a hole to accommodate the bathtub drain assembly.
Step 2 – Dry Fit Drain Assembly
Measure, cut, and dry fit the drain assembly. It’s best to run the overflow straight down and to use the same material (e.g. ABS, PVC, or Brass) when possible.
But in remodels you may need to adapt. Here I had to route around a floor joist. The flexible 90° elbow gave me more clearance than a plastic 90. I didn’t have one part in PVC so I hacked in a piece of ABS with ABS to PVC transition cement.
Step 3 – Install Drain Assembly
3.1 – Install Overflow
Install the overflow drain according to manufacturer instructions. For this Kohler Archer acrylic tub they called silicon between the rubber gasket and the tub. Then the overflow is secured to the tub-side with a provided metal flange and screws.
3.2 – Install Tub Drain
Install the bathtub drain according to manufacturer instructions. Here again they wanted silicone on the rubber gasket between the drain elbow and the bottom of the tub.
They also wanted plumbers putty under the drain flange. Some say plumbers putty will stain an acrylic tub. You can listen to some or to the manufacturer. I usually go with the manufacturer.
Screw the drain flange into the drain elbow using needle nose pliers or a drain wrench.
At this point do not tighten all the way.
3.3 – Connect Overflow to Drain
Finish the overflow to drain connection. Join ABS with ABS cement. Join PVC with PVC primer and glue. Join ABS to PVC with transition cement.
Give the drain flange a final tighten using a screw driver for leverage.
Step 5 – Dry Set Tub
Dry set the tub to make sure it sits level.
This particular tub was not sitting level on my level subfloor. There are a couple of fixes for this: One is to use plastic or wood shims and construction adhesive.
Another fix is to set the tub into a mortar mix, which is a mixture of sand and cement. This is a good idea even of the bathtub is level because it helps prevent creaks and gives the tub a solid feel under foot.
Step 6 – Mortar Mix
Most any mortar mix will do (e.g. s type mortar, mud bed mortar, etc.) Don’t use a fast set mortar like Rapid Set.
Here I’m mixing it on fairly dry to use as a support for the tub. I want it wet enough to squish out in some places but dry enough to shim and hold the tub up in other places as it dries.
For a level tub that you just want to solidify you can mix it wetter to make it easier to pour into the floor.
Plan Ahead Tip
If possible, before setting the tub, drive a nail to mark where the drain will exit the ceiling below.
Step 7 – Set Tub
Some tubs call for a support stringer, which is a 2×4 set along the back wall for the tub to rest on. This tub does not. Adding one would likely crack the tub once installed and stood in.
Place something in the tub like cardboard to protect it. Step into the tub and level it by methodically squishing it down into the mortar.
Once level, screw the flange to the studs using galvanized or stainless steel screws. Avoid cracking the tub flange by pre-drilling the screw holes and using shims wherever the studs do not touch the flange.
Step 8 – Attach P-trap
Use the nail you drove earlier to locate the tub drain to attach a P-trap. The trap holds water to prevent sewer gas and bugs from entering the house.
Again, join ABS with ABS cement. Join PVC with PVC primer and glue. Join ABS to PVC with transition cement. Here I used a homemade swab extension to reach into the ceiling and glue the drain pipe into tub drain.
Hold pipes together for 30 seconds after glueing to prevent push out. You want to glue to the depth of the socket.
A flexible coupling lets you connect plastic to cast iron. Here I installed a glued p-trap but it’s better to install a trap with a clean out plug or a screw trap like you find under a sink.
Step 9 – Shim Tub Skirt
Once the tub dried I went back and added wood shims under the tub skirt using construction adhesive.
Final Notes
When framing the space for your tub, where possible, place sideways studs at either end of the tub skirt to support any future shower doors.
Alright guys that’s one way to install a bathtub. Feel free to ask any questions in the comment section below.
