It is safe to tile over waterproof membrane. In fact, most shower installation systems these days are designed for you to install a waterproofing membrane or waterproof backer board prior to installation. You can also install floor tile directly over the elastomeric membrane. In all cases where you are installing tile over a waterproofing membrane, it’s best to use a thinset mortar you mix yourself. This mortar is of higher quality than the pre-mixed varieties and will provide a better bond between the waterproof membrane and tile.
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Do You Need a Membrane Under Tile?
If you are installing tile on the floor, walls, or ceilings of a shower, a waterproofing membrane or waterproof backer board is a must. If you do not waterproof your shower, water will seep through grout and tiles to soak into the wall. This will cause your tiles to fall out, your wall to degrade, and create the conditions for mold and mildew.
- It is essential to use a waterproofing membrane or waterproof backer board under your tile in your shower.
- It is optional, but recommended, to use an elastomeric membrane beneath floor tile installations.
If you are installing floor tiles, it’s a good idea to use an elastomeric membrane as a subsurface beneath the tile. This membrane flexes, which helps prevent cracked tiles. Using a membrane beneath floor tiles will increase the longevity of your tile installation.
Does Thinset Stick to Waterproof Membranes?
Pre-mixed thinset mortar does not adhere well to waterproof membranes. Instead, it’s essential to use unmixed, powdered mortar. If a pre-mixed thinset is used, it will not adhere well to the waterproofing membrane. This can cause tiles to pop off once the mortar dries. Powdered mortar that you mix yourself yields much better results.
- Do not use pre-mixed thinset mortar when installing tile over waterproof membrane.
- Use this powdered mortar for your tile installation.
- Mix powdered mortar with cool water until it reaches a peanut butter consistency.
When mixing a powdered mortar, add about 5 pounds of powder to a large bucket. Then, gradually add cool water as you mix the thinset with a trowel. Once the mixture has reached the consistency of peanut butter, it’s ready to spread over the waterproofing membrane with a trowel.
How Do You Install Shower Tile Over Waterproof Membrane [5 Steps]
The steps below are designed for a tile installation in a shower, over a liquid waterproofing membrane such as RedGard. If you are using sheets of elastomeric membrane for a floor tile installation, the process will be different than the one detailed below. Here’s a quick guide to your shower tile installation.
Prepare the Surface
Before you can paint a liquid waterproofing membrane onto shower walls, you must have installed a waterproof backer board such as a concrete board. Then, you must seal all of the joints between the boards with thinset adhesive and mesh tape. Standard joint compound and paper tape will deteriorate if used in a shower.
- Install a waterproof backer board for your shower walls.
- Seal joints in your shower walls using thinset adhesive and mesh tape.
- Do not use joint compound or paper tape—these will be destroyed by water.
- Apply several coats of mortar and sand between coats.
- Sand after the final coat to make sure the shower walls are smooth and even.
To achieve a smooth shower wall surface, applying 2–3 layers of thinset adhesive to the joints between the backer board is essential. Wait 24 hours between coats and sand before applying each new coat. After the final coat, sand the joints again to create a smooth, uniform surface for your waterproofing membrane.
Paint on Waterproof Membrane
Protect your bathtub or shower pan with a drop cloth. Then, use a roller to paint on your waterproofing membrane. Apply an even coat that fully covers the backer board. In corners and other areas, it may be essential to use a paintbrush to apply the membrane.
- Protect your shower floor or bathtub with a dropcloth.
- Use a paint roller and brush to apply this waterproofing membrane directly onto your concrete backer board.
- Allow several hours for the waterproofing membrane to dry before proceeding.
After painting, allow 2–3 hours for the membrane to dry. It may take longer for the membrane to dry in cool weather. Some membranes, such as RedGard, change color when they dry. This can help you determine when it’s safe to begin installing your tile.
Mix Thinset Mortar
Mix powdered thinset mortar for use during your tile installation. A high-quality powdered mortar will bond extremely well to your waterproofing membrane, resulting in a long-lasting tile installation. Pre-mixed thinset mortar bonds poorly to waterproof membrane and will cause tiles to pop up or fall off the walls.
- Mix a powdered thinset mortar with water for use over waterproof membrane.
- Avoid using a pre-mixed thinset mortar—these adhere poorly to waterproof membranes.
Use your tile trowel to mix your mortar with cool water until you achieve a peanut butter or cake batter consistency. It should be thin enough to spread easily, but thick enough that it adheres to the wall.
Use a notched trowel to spread your thinset mortar over a 2-foot by 2-foot area before tiling. When tiling a shower, it’s best to spread a small portion of thinset, install your tile in this area, and repeat. If you spread thinset on all the surfaces before installing tile, there is a chance the thinset could dry before you install your tile. If this happens, your tile will not adhere to the wall.
- Spread your thinset mortar in a small area and install tiles there before continuing.
- Do not apply thinset to all the surfaces at once. The thinset may dry before you can install tiles on top of it.
- This 3/8 X 3/8” square-notched trowel is ideal for most shower tile installations.
For most installations, a 3/8 X 3/8” square-notched trowel will spread an adequate amount of thinset to keep your tiles in place. This works well for ceramic tile, as well as glass and porcelain tile. Consult a tile expert if you are using very large or unique tiles, as they may require more or less thinset to hold them in place.
Press your tile into place on the thinset mortar. Make sure to press firmly enough that the thinset spreads to adhere the tile to the wall. Do not press so hard you break the tile. You can begin your design in the center of the wall, a corner, or an edge.
- Press tiles firmly into place to begin your installation where you desire.
- Cut tiles to fit where you meet corners and edges.
- Use spacers to keep tiles a uniform distance apart during installation.
Use tile spacers to keep your tiles at a uniform distance. This leads to a much more professional finished product. Just make sure to remove tile spacers before grouting and sealing your tile.
Can You Tile Over Shower Membrane?
Not only is it possible to tile over shower membrane, but it’s also essential. Waterproof membrane itself is not rated for the wear and tear of regular use, so any shower that has been treated with a waterproof membrane should be tiled before use. When tiling over waterproof membrane, keep in mind:
- Tile over a smooth surface that has been sealed with thinset mortar and sanded to a smooth finish.
- Apply the waterproof membrane to cover the backer board in the entire area where tile will be installed, including corners and small details.
- Use a powdered thinset mortar when installing tile over waterproof membrane.
- Avoid premixed thinset mortar when installing your tile over membrane—pre-mixed mortar adheres poorly to waterproof membranes.
These simple rules will result in a durable, professional tile installation in your shower. When applied correctly, a waterproof membrane protects your walls from damage and ensures the longevity of your tile installation.