How to Waterproof Shower Walls Before Tiling


 

Your bathroom is subject to water vapor and moisture daily. By ensuring that you waterproof shower walls before tiling, you can protect the area from mold, mildew, and wood rot.

Shower walls should be waterproofed before you install any tiles. A tile backer board is necessary to protect the substrate from water damage, while a waterproof membrane provides additional waterproofing protection to the area.  

Tiles and grout on their own are not waterproof, which means additional measures must be taken to protect the underlying structure behind the tiles. Choosing the right waterproofing method will depend on the type of substrate you use and the material of the bathroom tiles you install.

Tile requires a good base that should be level, stable, solid, and moisture-free before applying the cement or tile adhesive. 

 

Layers of Material Used for Waterproofing Shower Walls

creating thin shower grout lines with spacers

 

Waterproofing shower walls generally consists of various layers to provide a waterproofing system instead of one component providing the complete waterproofing solution.

To understand what is involved with waterproofing shower walls, you need to be familiar with the different layers that you’ll place behind your gorgeous tiling:

 

Substrate – A term that refers to any material that lays under the material that shows on the shower walls and floors. Tiles are attached to the substrate with adhesive. Substrate materials may or may not be waterproof.

 

Waterproof Membrane – A thin layer of material or liquid sealant that may be placed over drywall or another substrate material to prevent water from penetrating through it. 

 

Backer Board – A thin, hard cement and fiberglass board laid on top of the substrate. It may or may not be waterproof, depending on the manufacturer. Does not contain organic material like wood.

 

Uncoupling Membrane – Material used between the tiles and the substrate. The uncoupling membrane is designed to prevent cracks in tile and grout by absorbing stress caused by expansion.

 

Tile Adhesive – A mortar that covers the substrate and serves to glue tile to the substrate. Sometimes cement can be used instead. Adhesive is generally stronger though more expensive. 

 

Just remember that it’s the waterproof membrane itself—not the tiles—that truly prevents water damage to the walls beneath. 

And certain types of tiles offer more water resistance, even if they are not waterproof. This water resistance helps to limit the water penetration in the shower. 

Read  Are My Bathroom Tiles Waterproof? for an in-depth guide to the most water-resistant and waterproof tile materials.

Now let’s take a look at these layers that will sit behind your shower tile and protect your shower walls.

 

How to Protect Shower Walls Before Tiling

Cement Boards Substrate of Bathroom Shower Wall

 

As discussed, the substrate is a barrier material used behind shower walls and floors. A good substrate material will manage water and moisture to resist mold growth and prevent structural problems.

The substrate is determined as any surface underneath the tiles. Substrate materials could be:

 

  • Concrete 
  • Cement Tile Backer Board
  • Sheet vinyl flooring
  • Subflooring
  • Drywall
  • Plywood

 

The type of substrate you choose will determine whether you need to add an additional waterproofing membrane on top of it.

Regarding waterproof membranes, the International Residential Code (IRC) Section P2709.2 States:

The adjoining walls and floor framing enclosing on-site built-up shower receptors shall be lined with one of the following materials:

  1. Sheet lead
  2. Sheet copper
  3. Plastic liner material that complies with ASTM D4068 or ASTM D 4551
  4. Hot mopping in accordance with Section P2709.2.3
  5. Sheet applied load-bearing, bonded waterproof membranes that comply with ANSI A118.10.”

 

If you are installing a new shower or remodeling your existing one, check what the local building codes stipulate for your area before you begin your project.

But the most important thing to remember is that once you have installed the waterproof membrane, anything you adhere to the surface of the membrane such as tiles and grout will divert water away from the substrate. 

 

Tile Backer Board to Help Waterproof Substrate 

A tile backer board is often used to provide the first line of defense in creating a waterproof substrate. The backer board is often placed over porous materials like plywood and drywall, which can rot easily if exposed to moisture. 

A tile backer board is installed onto the substrate to assist in the fight against water damage and prevent ideal environments for mold and mildew to thrive. 

 

Waterproof vs Water-Resistant Materials

Are Bathroom Tiles Waterproof

A waterproof material will not allow any water to penetrate ever. A water-resistant material can prevent water from penetrating the material for a limited amount of time. 

Often, backer boards will be water-resistant. But to completely waterproof the shower walls usually requires the application of a waterproof barrier over the tile backer board, but the choice of tile backer board is important.

 

Cement Tile Backer Board  

Cement Backer Board to Waterproof Shower

A cement tile backer board is the best option to use on the shower walls. A cement board is used as a tile backer board for applying waterproofing solutions and sealants like a liquid membrane, uncoupling membrane, plastic sheeting, or a pre-waterproofed board.

For extra waterproofing protection when using a tile backer board, a waterproofing membrane can also be applied underneath the backer board to prevent water from leaking through the wall studs into the substrate. Check with the backer board manufacturer before purchasing the board to see if this step is a requirement.

 

3 Materials NOT to Use as Tile Backer Board in the Shower

Don't use Plywood to Waterproof Showers

 Although there are quite a few materials suitable for use in the shower, there are a few that aren’t!

 

  • Green board is allowed by some local building codes as it is a bit more water-resistant than drywall, but it has become outdated as there are better products to use.

 

  • Drywall is not acceptable as a wall tile backer board as it can disintegrate or turn moldy if it comes into contact with water.

 

  • Plywood should never be used for wall tiles unless it has been specially treated for a damp environment.  

 

The Best Types of Backer Board for Bathroom Walls

 

The following tile backer boards are the most popular for use on bathroom walls:

 

MATERIALPRODUCTPROPERTIES
CBUHardiebackerA mineral-based board, resistant to mold, mildew, and rot. Stronger and more durable than gypsum board
Polystyrene Foam BoardKerdiA lightweight, waterproof panel. An excellent substrate for bathroom tiles
GypsumGlasRoc HPre-primed water-resistant acrylic surface. Perfect for bathroom walls exposed to moisture or water
Glass mat gypsumDensShieldWater-resistant silicone-treated gypsum reinforced by fiberglass mats. More water-resistant than cement boards. Perfect for shower walls. Watch this video for installation of DensShield Backer Board.
Foam BoardPermaBaseA completely waterproof backer board designed for interior tiles. Perfect for shower wall, tub surrounds, and backsplashes

 

Tile Backer Board Brands: Pros, Cons and Pricing

A great way to waterproof a shower wall is Cement Backer Board

The table below gives an overview of the pros and cons of the most popular tile backer boards available for use on bathroom walls. Choose the board that suits your budget that fits your space.

 

BRANDPROSCONSPRICE
Hardiebacker- Can be installed over drywall
- Waterproof composition
- Moldblock technology protection
- HydroDefense technology offers moisture and damage protection
- Easy to cut, score, snap and install
- Compressive and flexural strength
- Has excellent tile adhesion properties
- Glass and fiber-free
- Lifetime warranty from the manufacturer covers labor and materials
- Generates little debris and dust when cut
- Boards available in different sizes and thickness
- Impact resistant

- Costly material
- Heavier and more brittle than gypsum
- Requires the purchase of cement board screws
- Requires an additional waterproofing sealant
3 x 5 feet

¼-inch

$12.37

½-inch

$11.98

Available from Lowes
Kerdi- Fully waterproof and vapor-tight
- Does not require a surface waterproofing membrane
- Lightweight material
- Easy to cut
- Dust-free installation
- Ready made boards won't deteriorate when exposed to moisture
- Reinforced with a fleece webbing material
- Requires additional waterproofing on seams and joints
- Thinset required to create a bond
- Wicking issues during the installation process
3 x 5 feet

¼-inch

$76.03

Direct from supplier Schluter
Glasroc H- Reduced water absorption rate
- Prevents mold and structure damage
- A non-combustible product
- Lightweight material, easy to install
No reviews4 x 8 feet

¼-inch

$64.99

Available from Rona
DensShield

- Moisture resistant
- Prevents the growth of mold
- Stops water at the surface
- Lightweight material, easy to install
- Does not require an additional moisture barrier
- Easy to cut using a utility knife
- Can be installed using regular rust-resistant drywall screws
- 20-year limited manufacturers warranty
No reviews4 x 8 feet

¼ inch

$48.97

Available from Home Depot
PermaBase- Greenguard certified
- Designed to withstand prolonged exposure to water
- Waterproof foam core
- Mold and mildew resistant
- Impact-resistant
- Lightweight and durable
- Easy to cut
- Quick installation
- 30-year limited warranty from the manufacturer
- Requires additional waterproofing on joints and seams
- Material is not recyclable or biodegradable
3 x 5 feet

¼-inch

$10.78

Available from Lowes

 

What Are the Best Waterproofing Membranes to Use on Shower Walls?

Waterproof Bathroom Tile Membrane

Cement, some tile backer boards, tile adhesives, grout, and built-in water-resistant membranes are not 100% waterproof, but they are water-resistant. 

In other words, these materials do not completely waterproof your shower. So the best solution is to apply a waterproofing membrane over the shower walls or tile backer board before tiling.

Adding a waterproofing solution will give you a second line of defense. Let’s explore three types of waterproofing membranes:

  1. Uncoupling Membranes  
  2. Liquid Waterproofing Membranes 
  3. Polyethylene Fabric Membranes

 

Uncoupling Membranes for Concrete Walls

You can use an uncoupling membrane between the tiles and the substrate. It’s especially useful for concrete substrate. 

Due to temperature and humidity changes, tile laid on top of concrete can fracture and crack as the concrete beneath it expands and shrinks.

The uncoupling membrane is designed to prevent cracks in tile and grout by absorbing stress caused by expansion.

 

The Schluter-Ditra Uncoupling Membrane 

Covers 323 sq feet. Designed as a waterproof layer to manage moisture between the tile and the substrate. Designed for ceramic tiles, DITRA provides load distribution support for the tile.

Features of the Schulter-Ditra uncoupling membrane:

  • Easy to measure, cut and install.

 

  • Simple to follow instruction manual provided

 

  • Easy to follow videos on the company website

 

  • The roll weighs 39 pounds

 

  • Dimensions 14 x 14 x 40 inches

 

See This Uncoupling Membrane on Amazon.

 

Liquid Waterproofing Membrane for Bathroom Walls

A liquid membrane is applied over the entire backer board or substrate surface to provide the most complete waterproof coverage. Multiple coats must be used for the best protection when using a liquid sealant. Watch this excellent video from Custom Building Products about liquid waterproof membranes.

 

ARDEX S 1-K One-Component Waterproofing Crack Isolation Liquid 

This membrane is a load-bearing waterproofing solution for substrates bearing tiles exposed to water. Perfect for use as a bonding material for tile and stone.

Features of the ARDEX S 1-K:

  • Easy to use, waterproof liquid membrane

 

  • Easy to apply using a 2 coat system

 

  • Applying using a paintbrush or roller

 

  • It can be used in all wet areas before the installation of tile

 

  • It can be used on various substrates

 

  • Provides repairs to cracks of up to 1/8-inch

 

  • Available in a 1-gallon tub

 

  • Covers 56.75 sq ft using 2 coats per 1 gal

 

See ARDEX Waterproofing Liquid on Amazon.

 

Polyethylene Waterproofing Membrane for The Bathroom Wall

 A waterproofing membrane made from the highest-quality materials, each roll is quality-controlled by the manufacturer. (In the section below, there’s a video by This Old House that shows how to install this type of membrane in your shower.)

Polyethylene waterproofing is designed for moisture protection in your shower and bathroom. Each sheet is tear-resistant but is flexible enough to mold to any shape that it is placed over.

 

Waterproofing Polyethylene Fabric for Shower Walls

Features of this Polyethylene Waterproofing Membrane:

  • Thick, durable, tear-proof, and flexible

 

  • A uniform thickness of 8 mils per sheet

 

  • Pliable, easy to fold to use in corners

 

  • Each roll measures 3.3 x 3.3 feet and covers 108 sq feet

 

  • Extremely low water vapor permeability

 

  • Easy to install

 

  • Guaranteed vapor and waterproof

 

See Waterproofing Polyethylene Fabric for Shower Walls on Amazon

 

 

Pro Tip: Apply a primer to the surface or substrate before installing any waterproof membrane to improve the adhesive bonding. Also, seal the joints using waterproof sealing tape or mesh.

 

How to Waterproof Shower Walls Before Tiling

 

Without waterproofing, water will seep through the substrate and could cause long-term damage to the structure. Bathroom mold can lead to costly repairs. Watch the video below from This Old House to see how to waterproof your shower walls with a waterproof membrane before tiling.  

 

 

 

So, Do I Need To Waterproof My Shower Walls Before Tiling?

Waterproof Bathroom Wall Before Placing TIle

To keep your bathroom and, in particular, shower walls free from mold, mildew, and rot, it is necessary to waterproof the area. Waterproofing prevents water from leaking into the structure of your home, causing expensive to repair damages.

Tiling and grouting the shower walls does not necessarily make them waterproof. This is why you’ll want to install a tile backer board and possibly also a waterproof membrane before you lay tile.

If you’re looking for ideas on how to paint over your backer board, read this article Do You Need Waterproof Bathroom Paint? Yes and No!

And be sure to check out my ultimate guide to bathroom tile, which includes resources about bathroom tile materials, bathroom tile colors, tile finishes,  waterproofing bathroom walls and tile, grouts, sealants and more. 

Pro Tip: If you’re in the middle of a bathroom remodel, download my free Save Big $$$ Cheat Sheet. You’ll get designer hacks that can literally save you thousands of dollars. Just fill out the form below.

Shana

Shana Burg is a bath enthusiast, content strategist, and award-winning writer. She is the founder of bathtubber.com.

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