Bathtub Replacement in Old Bathrooms: Our Step-by-Step Guide

Posted by Jeff Patterson on

Learning how to do a bathtub replacement in an old bathroom is priceless.

Today we're going to share tons of great tips and prepare you for a successful bathroom remodel.

Our tutorial is perfect for homeowners who's home is older.

Let's dive in and get you feeling more confident about how to replace a bathtub.


Why You Should Level a Subfloor for Bathtubs

Old homes are never level.

We had to level the subfloor, but only where the new tub was going.

How to level a bathtub subfloor


Leveling the entire bathroom subfloor would have created a big problem at the doorway. Steve mentions this in the video. Had the floor been leveled there would have been over a 1 inch difference between the tile in the bathroom and the wood floor in the hallway.

Not good!

In addition, the wood in the bathroom couldn't be removed because it was resting under the stud wall. This is the reality of remodeling older homes.

Again, Steve does an excellent job explaining the situation in the video. You might be in the same predicament!


How to Prep for an Americast Bathtub 

Installing bathtubs is different for each type of material.

Acrylic, steel, and cast iron are the three main types you'll see in stores.

The Americast tub in today's tutorial is made by American Standard. Americast is a special type of steel with a porcelain enamel finish. Read more about it over on American Standard's site. 

It's way lighter than cast iron and has a durable finish that's more resilient to scratches than steel tubs.

You can grab an Americast tub for $325 on up.

The first step is to add a 2x4 ledger board to the studs.

How to Measure for a Tub Ledger Board

Screw the 2x4 to studs using 3 inch deck screws and ensure it's level.

How to add a ledger board for bathtubs

Americast tubs have integral overflows which helps eliminate the chance of leaks.

Integrated Waste Overflow in Americast Tub

We chose the 60" Princeton tub with a right hand drain orientation. You'll see in the video that unfortunately the drain sat over the joists.

Know Drain Location

This kind of sucked. But we made it work.

After picking your tub, installing the ledger, and prepping the drain location it's time to install the tub plumbing.


Installing Bathtub Plumbing and Making it Leakproof 

Silicone sealant should be applied to the tub drain location.

Silicone Drain Bathtub Drains

And to the bottom of the drain assembly.

Silicone Drain

We get this question a lot: why use silicone instead of plumber's putty?

Silicone stays flexible and watertight longer than plumber's putty.

The bottom line:

Silicone is better at preventing leaks than plumber's putty.

Assemble the drain per the directions and apply pipe dope to the threads.

Pipe Dope Bathtub Drain

Use Channellock pliers and a tub wrench to hand tighten the drain.

Then turn the nut on the drain with the Channellock pliers 1/4 to 1 full turn.

ABS was used in this house. As such, we had to add an ABS adapter to the drain.

Tighten Bathtub Drain Nut

The pipe dope helps keep a watertight seal between the ABS and drain.

Assemble the tub P-Trap.

Tub P-Trap

Then dry fit the tub.

Dry Fit Tub

We can't emphasize this enough:

Installing bathtub plumbing before setting it will make your life easy!!

That's the big reason for adding the P-Trap to the tub before getting it down on the subfloor.

Pull the bathtub off the subfloor. Dry fitting cast iron tubs is a pain in the butt. As you'll see in the video, Steve can heft the Americast tub on his own.


The Final Steps for a Bathtub Replacement Project

Americast tubs have a foam insert on the bottom.

You could set the tub on a level subfloor and be done.

But the directions say a bedding material is acceptable under the tub.

We mixed up mortar and poured it on the self-leveler.

Then a bead of silicone sealant was placed on the stringer.

Apply Silicone to Ledger

The sealant on the stringer and mortar stop the tub from creaking.

Here's the deal:

If your bathtub installation instructions call for mortar...USE IT.

We've heard too many stories of people tearing out new bathtubs after a few years because of leaks. Mortar helps prevent this from happening.

Guess how much a 50lb of mortar costs?

$5 to $15

Whereas a new tub costs way, WAY more.

We set the tub in mortar and double checked that it was level.

Level Bathtub

Finally, the tub was attached to the studs using galvanized screws and washers.

Watch our video for more tips and to see how Steve installed this tub in less than an hour.

Check out our NEW Store:

We've selected the tools and supplies with you in mind. Making bathroom remodeling easier, faster, better!


See you in the comments,

Jeff Patterson






P.S. If you're doing a DIY bathroom remodel come back up here after leaving your comment and grab our free guide 'How to Remodel a Bathroom in 10 Days or Less', it has a ton of great tips.

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