Waterproof bathtub shower walls over drywall

Waterproofing your bathtub shower walls ensures that your bathroom walls remain safe and free from water damage. It will save you time and money and you’ll have peace of mind knowing that your walls are waterproofed and ready for tiling.

Even if you’ve never experienced it before, a behind-the-scenes bathtub leak is scary and unpredictable. 

Paint bubbling or flaking off the wall, sneaky signs of mildew, or even worse, a droopy ceiling below.

Eventually, it makes itself known like an unwelcome visitor, and you’ll want it to go away fast.

When that happens, you know you’re in for a ton of work and money down the drain. 

The next time you’re renovating your bathroom, use this opportunity to waterproof your bathtub shower walls and avoid a disaster later.

In this post, I will share how you can waterproof your shower walls before tiling using Schluter Kerdi Tubkit.

WHY I CHOSE SCHLUTER KERDI

I first heard about Schluter Kerdi from a plumber who highly recommended using this system. 

I decided to use it when I tiled the shower in our basement. 

Here is what I loved about installing this product:

1. The system is completely waterproof.
2. It’s designed for the average DIYer to install.
3. And you can install it over drywall. 

Bear in mind, this is not the cheapest option, but it’s very effective.

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Here’s what you’ll find in the tub surround kit from Schluter: 

• Waterproof membrane
• Kerdi band (membrane strip)
• Kerdi fix (waterproof sealant)
• Pipe seal 3/4″ (shower/tub)
• Mixing valve seal (faucet)

If you plan on installing the membrane from ceiling to floor, you will need additional Schluter Kerdi Membrane because they do not provide enough.

I also recommend purchasing another Schluter Kerdi 3/4″ pipe seal. The kit includes one but you need another for the shower head pipe and bathtub spout. I’m not sure why they don’t provide two. 

Also, if you have a window in your bathtub, you will need to purchase the Schluter Kerdi Inside Corners. 

If you are planning on tiling your bathroom floor as well as the bathtub shower walls, it’s easy to make your whole bathroom waterproof. 

You will want to prep your floor for tile using Schluter Ditra, and I explain all the benefits and how to install it in the link provided. 

Now, let’s get into installing the shower wall waterproofer.

Step 1: Prep the walls 

Before you can start, you need to prep the area, which might include demolishing what is already there. 

For our bathroom renovation, we removed the old tiles and were left with some very beat-up walls. 

Usually, you would cut out and remove the damaged drywall and replace it with new drywall. But in our case, our walls are plaster, so I had to patch and repair the walls instead of adding new drywall. 

When using a waterproof membrane, you must ensure that the surface (wall) is smooth. 

So after fixing our bathroom walls, it looked like this:

You should paint your walls and ceiling before installing the waterproofing membrane. However, you do not need to paint the areas where the membrane will be installed over it.

Step 2: Cut the membrane

Cutting the membrane is easy. All you need is scissors! When you’re ready to cut it, simply follow the grid system.

But before you can cut the membrane, you need to determine if the membrane is going up to the ceiling or just past the shower head. 

Either option is fine; the important thing is that the membrane and tile end above the shower head. 

SIDE NOTE: If you decide to take the membrane to the ceiling, you will need to purchase about 8’ more because the kit doesn’t have enough to do this. 

Also, make sure to overlap any joint by at least 2”. 

SIDE NOTE: The membrane grid system has a two-inch area so you know where to overlap. 

You should also cut the membrane so it goes past the bathtub by at least 3”. 
TIP: When you tile a bathtub surround, you want the tile to extend past the edge of the bathtub by around 5”. This is why you should extend the waterproof membrane as well to give you a completely waterproof system.

To determine where and how you need to cut the membrane, use a tape measure and a piece of paper to measure your bathtub surround.

After, you will transfer the measurements to the membrane using a pencil. 

Then, you’re ready to cut with scissors.

STEP 3: Mix the thinset

You need a special type of thinset to install the Schluter Ditra. I recommend using Schluter’s version called All Set to get the best results.

Follow the exact instructions on the package.

I used a scale to weigh the water and the mix. This was an easy and precise way to ensure I got the correct consistency. 

I found it helpful to use half a 50-pound bag every time I mixed a new batch. There are two reasons for this: 

1) It was a good amount to work with at a time (didn’t set up before I would use it all)

2) If you mixed the full 50-pound bag all at once, you would need a bigger drill, or you would risk overheating your cordless drill. 

To begin, fill the bucket with water and pour in the mix.

Next, use the drill paddle attachment to mix the thinset (mortar). 
Make sure you follow the instructions on the bag. The package will tell you the amount of time that you need to mix. Normally, there’s a mixing phase, a rest, and then another mixing session.

The product I used required a mix for 5 minutes, rest for 10 minutes, then mix for another 3 minutes before it was ready.

Step 4: Waterproof around the bathtub

After you mix the thinset, you can install the membrane to the bathtub shower walls. 

You will start by using the Schluter Kerdi Fix.

Apply a bead of silicone around the bathtub to give you a waterproof finish at the seam of the drywall and bathtub.

SIDE NOTE: You can also use Schluter’s video on how to install Schluter Kerdi Tubkit.

A bathtub is different than a shower, which goes all the way down to the floor. You need to apply the Schluter Kerdi Fix to give you the waterproof finish between the rim of the bathtub and the wall. 

After you have piped the Kerdi Fix all around the bathtub, put a strip of the Kerdi Band (membrane strip) along the bathtub.

Using the V-notched trowel, apply the thinset to the wall, ensuring there are grooves from the trowel notches in the thinset.

SIDE NOTE: You can work in sections. I like to work on one wall at a time. Watch my YouTube video on how to install Schluter Kerdi Tubkit to see what I’m talking about.

You will apply the thinset far enough up the wall to allow the band to adhere. 

After the area surrounding the bathtub is covered with thinset, place the Kerdi Band membrane on top. Adjust it if needed. 

SIDE NOTE: You want the membrane strip to be as close to the bathtub as possible. This way, the Kerdi Fix will set the membrane to the wall as well as the bathtub, giving you a waterproof finish. 

Use the taping knife to smooth the strip and remove any excess thinset from the area. 

Step 5: Install the waterproof membrane to the wall

Now, you’re ready to move on to waterproofing the walls.

Take a damp sponge and wipe the wall. It’s recommended to wet the wall with a damp sponge to help the thinset adhere to the drywall.

Then, apply the thinset to the area with the trowel. 

You will cover the full wall with the thinset, ensuring there are grooves from the trowel notches in the thinset.

After the area is covered with thinset, place the membrane on to the area. I like to start at the top and then work my way down. Adjust it if needed.

Then, use the tapping knife or flat side of the trowel to embed the membrane to the wall by adding pressure to the flat edge and pulling toward the edge of the membrane. This will remove any bubbles or excess thinset but, most importantly, allow the membrane to adhere to the floor.

Remove the excess thinset that seeps out from the membrane.

You will most likely have extra thinset on the wall after embeding the membrane. To remove, use a damp sponge again to wipe that area of the wall before it has time to cure. 

SIDE NOTE: Remember to overlap the wall corners and any membrane pieces. You are overlapping them to ensure proper coverage. 

Repeat this process for all the walls of the shower walls. 

Step 6: Install the other seals and membrane corners

When you’re ready to apply the pipe seal or valve seal, apply thinset on top of the wall membrane in the area where the seal will be placed. 

Again, make sure there are grooves from the trowel notches in the thinset.

Place the seal, then use the taping knife to remove any excess thinset, just like you did when installing the wall membrane

The corner membrane pieces (for windows, niches, etc) are installed the same way as the seals: applying thinset, placing, and using a flat edge to adhere the membrane to the area

SIDE NOTE: You can also use the Kerdi Band (membrane strip) to waterproof and joints. 

Then, let everything dry and cure for at least 24 hours

FULL PROJECT VIDEO:

Are you someone that does better with visuals? Check out the full DIY waterproof bathtub shower walls over drywall project video below and don’t forget to subscribe on YouTube so you don’t miss out on future projects!

With a little bit of careful measuring and cutting, this is an easy project. And it’s one that is essential for protecting your bathroom walls from water damage.