Tillie Doyle
When building a shower, one of the most important considerations is ensuring that it is waterproof. A common question that arises is whether it is possible to put cement board down over a shower pan to create a sturdy and waterproof foundation for tiling. While some sources advise against using cement board on its own, as it may lead to leaks, others suggest that it can be done if the shower pan is clean, dry, and properly prepared, with the cement board secured using appropriate fasteners. In addition, it is recommended to use waterproofing products such as RedGuard, Hydroban, or Kerdi over the cement board before tiling.
Characteristics and Values Table:
| Characteristics | Values |
|---|---|
| Installation | Install cement board directly on the shower pan's surface. |
| The shower pan should be clean, dry, and properly prepared before attaching the cement board. | |
| Use appropriate fasteners to secure the cement board to the shower pan, following the manufacturer's instructions. | |
| Waterproofing | Cement board is not waterproof. |
| Use a waterproofing membrane like RedGuard, Kerdi, or AquaDefense. | |
| Slope | Use a pre-sloped shower pan or create a slope with a drypack sand mix. |
| The slope should direct water towards the drain. | |
| Mortar | Use a mud-bed or mortar base to support the cement board. |
| Tape and mud the corners, seams, and screws of the cement board. | |
| Tiling | Allow the mortar bed to dry before tiling. |
| Ensure the cement board has a solid backing before tiling. |
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What You'll Learn
The correct placement for cement board over a shower pan
It is important to note that cement board is not waterproof, so a waterproof membrane, such as RedGuard or Kerdi, should be installed underneath. The shower pan should be built in two stages, with each stage using the same "dry pack" mixing method. The first layer of the shower pan should be a waterproofing membrane to establish a drainage path for water if the top layers are compromised.
When preparing the dry pack sand mix, wear respiratory protection and mix it with about 1/4 of the recommended amount of water. The correct consistency has been reached when you can form a "snowball" with the mix that does not crumble when tossed in the air. Once the mix is ready, pour it into the shower base and use a hand level to create a level perimeter. After the perimeter is level, fill in the center of the shower pan and use a straight edge to confirm a smooth slope from edge to drain.
After the dry pack bed has cured for 24 hours, you can install the slope system of guide sticks to ensure a correct slope to the drain. Install the mud-bed, guided by the slope sticks, and pack it well. Once dry, waterproof the mud-bed and the walls with two good coats of RedGuard, AquaDefense, or a similar product. This will create a waterproof shower, even without tiles.
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Using a waterproof membrane
Waterproofing your shower is an important step to prevent serious issues down the line. While tiles are virtually waterproof, the grout in between them is not, and will absorb water over time. This can cause water damage to the underlying structures, leading to mould growth and costly repairs.
To prevent this, a waterproof membrane should be installed. There are four main types of waterproofing membranes: sheet membranes, liquid membranes, foam wallboards, and foam shower bases.
Sheet membranes, such as the Schluter Kerdi membrane, are placed directly beneath the tile layer to prevent water penetration into the subfloor. It is recommended to use a manufacturer's shower system to ensure effective waterproofing and efficient drainage. Before applying the membrane, cover the joints with a thin-set and fibreglass tape to strengthen them and bridge gaps.
Liquid membranes can also be used to waterproof the shower walls and ceiling. Multiple layers may be required, so be sure to follow the manufacturer's instructions. Do not use a liquid membrane if you already have a shower pan liner, as this will create a "mold sandwich".
When installing a waterproof membrane, it is important to avoid penetrating the membrane with nails or screws, as this can lead to shower failure. Water will migrate through any holes and reach the structures behind it.
Additionally, when using a cement board, it is recommended to install it over a waterproof membrane to ensure that the shower is fully protected from water damage.
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Preparing the shower pan
Planning and Materials
Before beginning any work, it is important to consult your local building codes and guidelines, such as the Tile Council of North America (TCNA) Handbook and ANSI108.1, to ensure your project complies with regulations. Estimate the amount of material required, considering a standard depth of 2" for the shower area. Use a slab calculator to determine the required volume of materials.
Pre-Slope Installation (Optional)
Some sources suggest the use of a pre-slope system, such as the Oatey Perfect Slope, to ensure a correct slope towards the drain. This step may be omitted if you are confident in achieving the correct slope with your mortar bed.
Mortar Bed Installation
The first step is to prepare a dry-pack mortar bed, also known as a mud bed. This will serve as the foundation for your shower pan. Begin by pouring a sand mix into a mortar pan or bucket, and gradually add water, mixing until you achieve a consistent, moldable texture. The correct consistency should allow you to form a moldable "snowball" that can be tossed a few inches without crumbling.
Once you've achieved the right consistency, spread the dry-pack mortar mix onto the shower base, creating a level perimeter around the shower pan. Use a rubber or wooden float to tamp down the mix, ensuring a level surface. Check the level from all sides and across the edges. Then, fill in the center of the shower pan, establishing a rough slope towards the drain.
Waterproofing
Before installing the cement board, it is crucial to waterproof the mortar bed. Cover your pan with a liner or waterproofing membrane, such as RedGuard, AquaDefense, or Kerdi. Nail the liner at least 8 inches up the studs and wrap it over the curb, nailing it on the outside only. This will create a waterproof barrier that prevents water from seeping into the underlying structure.
Cement Board Installation
Finally, you can install the cement board. Position the cement board at the bottom of the pan, over the liner, and screw it into the studs. Ensure the screws are at least 6 inches up from the pan. Tape and mud the corners, seams, and screws to create a smooth surface.
By following these steps, you will have successfully prepared the shower pan for your cement board installation, creating a solid foundation for your stand-up shower.
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Using a pre-slope system
A pre-slope system is an integral step in building a shower pan, even if it may seem redundant. The purpose of the pre-slope is to encourage water towards the drain and prevent pooling. The pre-slope sits on top of the subfloor and sets the proper negative slope for each layer that will sit above it.
The most common method for constructing a pre-slope is with a mixed cement and sand deck mud that has a consistency that will allow it to be balled up in the palm of your hand. Using a trowel, a 2x4 wood piece, or a level, you can pack the deck mud up to the desired height around the shower pan. It is important to use the least amount of water possible when mixing the deck mud, only adding enough to bind the cement. An alternative to this method is to use a pre-manufactured product that can be cut to the exact size of your shower pan and comes with an accurate negative slope that leads to the drain.
When installing a pre-slope, it is important to measure the distance from the shower drain to the surrounding walls and corners, including the nearest high point on the shower curb. For each foot, a 1/4 inch negative slope is recommended to encourage proper drainage. Once the pre-slope is installed, a liner, such as PVC, should be placed on top, followed by the top base layer.
Some sources mention the use of a waterproof membrane, such as RedGuard or Kerdi, to be placed over the cement board to prevent water wicking. It is also recommended to install backer boards about 1/4 inch above the pan to prevent wicking.
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$50.59
Installing the cement board
Installing cement board in the shower requires careful preparation and execution to ensure a successful and durable installation. Here is a step-by-step guide to help you through the process:
Prepare the Surface:
Before installing the cement board, ensure that you have a solid and level surface to work on. The surface should be clean and free of any debris or residue. If necessary, use a suitable levelling compound to create a flat and even base.
Install a Waterproof Membrane:
As cement board is not waterproof, it's essential to install a waterproof membrane to protect the shower pan from moisture damage. Products such as RedGuard, AquaDefense, or Kerdi can be used for this purpose. Follow the manufacturer's instructions for proper application.
Prepare the Cement Board:
Cut the cement board to size, ensuring it fits the dimensions of your shower pan. Handle the cement board carefully to avoid injury and breakages.
Secure the Cement Board:
Install the cement board onto the shower pan, ensuring it is secure and stable. You can use screws or nails for this step, but ensure they are long enough to penetrate the studs by at least 6 inches, as mentioned in one source. One source suggests using Durock screws with the backer-on screws. Place the screws 1-5/8" apart. Ensure the cement board sits firmly on the liner and rests about 1/4 inch above the pan, as a gap is recommended by multiple sources to prevent moisture wicking.
Tape and Mud:
Tape and mud the corners and seams of the cement board to reinforce the installation. One source suggests using a mapei tile porcelain and fiberglass seam tape. Cover the screws with mud as well. Ensure the tape and mud application is smooth and even.
Install the Slope System:
Install a slope system, such as guide sticks, to ensure proper drainage. This step will help you create the correct slope for the shower pan.
Install the Mud-Bed:
Following the slope system as a guide, install the mud-bed and pack it well. Make sure the mud-bed dries completely before proceeding to the next step.
Waterproof the Installation:
Once the mud-bed is dry, apply two good coats of waterproofing material, such as RedGuard, AquaDefense, or a similar product. This step will ensure that your shower is fully waterproof, even before tiling.
Remember to carefully follow the instructions provided by the manufacturers of the products you use, and always take the necessary safety precautions when undertaking such projects.
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Frequently asked questions
Yes, you can put cement board down over a shower pan.
To install a cement board over a shower pan, ensure the shower pan is clean, dry, and properly prepared. Then, use appropriate fasteners to secure the cement board to the shower pan, following the manufacturer's instructions.
There are a few methods for installing a cement board over a shower pan. One method is to install the cement board directly on the shower pan's surface, using appropriate fasteners to secure it. Another method is to install the cement board about 1/4 inch above the pan and use a backer rod or sealer to prevent wicking.
It is important to ensure that the shower pan is properly waterproofed before installing the cement board. Additionally, when using the cement board with a mortar bed, consider whether to leave a gap between the two to prevent moisture wicking.
