Whenever installing tile in any area of your house, you need a special substrate or base layer. In showers, the standard substrate is tile backer, also called cement board or cement backer board.
Ceramic and porcelain tile, more than almost any other surface material, needs a stable, flat, flex-free substrate. Even the slightest amount of movement in a building structure can telegraph to the tile and crack it. Besides, because showers and bathtubs are wet areas, they need a substrate that will not be damaged by moisture, just in case a crack in the tile or grout lets water through to the backer.
Technically called a cementitious backer unit (CBU), well-known brand names of tile backer include Durock, Densshield, HardieBacker, and WonderBoard. All are made of 100-per cent inorganic materials that will not rot, shrink, delaminate, or decompose when exposed to moisture. There are several acceptable applications of cement board in the shower.
Adding a tile wall to the shower is a great way to breathe new life into a bathroom. Not only will a tile wall look great, but it also has durable and long-lasting qualities. However, adding the right kind of drywall board behind the tile can be challenging, especially considering all the moisture the wall will have to withstand throughout its life. Luckily, there are a few types of drywall that are perfect matches for any shower, including a blue board, green board, and cement board.
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Type of Drywall Board
Regular drywall can be used as a base for tiles in a shower, but only as an absolute last resort. Even in the best of scenarios, the tile and grout will eventually wear down, leaving behind a clear route for water to seep through and soak into the drywall. If you have to use regular drywall, then a water barrier must be inserted behind the drywall and the wall frames. This is done to help prevent water from damaging the structure of the wall. Additionally, using regular drywall can compromise the integrity of the tile as water will disintegrate the drywall.
Blueboard is a type of drywall that is frequently used for a tile wall in a shower. Not only is it water-resistant, but the blue board is easy to find and inexpensive, making it an ideal option for those on a budget. Furthermore, the blue board is not difficult to install. The process of installing blueboard is similar to that of regular drywall and can be done with little prior experience. Although it is water-resistant, you will need to make sure all seams are properly covered and place some water barrier between the tile and blue board. Fortunately, there are plenty of products for this purpose, including RedGard and Kerdi membranes.
Greenboard shares some of the same qualities as a blue board, with the main difference being how the material is made. Greenboard is created with recycled materials, which makes it ideal for an environmentally-conscience choice. The installation process of the green board is the same as the blue board, and a water barrier will be needed to keep moisture away from the board. The same types of water membranes can be used with both blueboard and green board. The important thing to keep in mind is that without a water barrier, the tiles will leak water, making a water barrier behind the tile a critical step in installing any drywall.
Cement board is by far the heaviest type of drywall used in tile wall applications and the most resistant to water. While it may be heavy, installing cement board is just like installing drywall, with a few minor differences. For starters, the cement backer board will need to be cut to the proper dimensions with a jigsaw. Next, properly secure the board to the wall’s structure via concrete screws. Unfortunately, drywall screws will not work. After applying some seam tape to cover joints, a waterproof membrane should be added to prevent any leaks. In addition to the water barrier, it’s a good idea to install a vapour barrier behind the cement board. This can be in the form of plastic sheets and will help minimize damage if water does make its way through the board.
Best Types of Tile Backer Board for the Shower
Cement Board and Plastic Sheeting
In this highly convenient, inexpensive, and popular application, a moisture barrier of 4- or 6-mil-thick plastic is installed directly over the wall studs. Then, the cement board is installed on top of the plastic sheeting. Screws secure the cement board to the wall studs. Tile is laid onto the cement board with thin-set mortar or mastic.
Cement Board and a Liquid Membrane
In this application, the cement board is installed directly onto the studs. No plastic sheeting goes behind the cement board. A liquid waterproofing membrane, such as RedGard or Hydro Ban, is applied to the cement board and allowed to cure. Then, tile is installed over the membrane.
Cement Board and a Sheet Membrane
Cement board is installed directly on the studs with no plastic sheeting behind it. Waterproof sheet membrane such as Schluter Kerdi is applied to the cement board with thin-set adhesive. After the thin-set has dried, tile is applied to the sheet membrane with thin-set. Kerdi can also be installed directly over standard drywall in a shower because, when installed correctly, it creates a continuous waterproof barrier.
Membrane-Faced Board Only
One type of tile backer board is made with a water-resistant facing on both sides of the board. Georgia-Pacific’s DensShield is one such product. The facing serves as an integrated waterproofing membrane, so you don’t need to install a separate layer of plastic behind the tile backer or a sheet membrane over the backer. As with the other applications, thin-set mortar is then applied to the board’s surface, followed by tile and grout.
Unacceptable Shower Backer Boards
Several traditional tile installation methods used materials that are no longer considered acceptable for shower applications.
- Drywall: It takes just a little moisture for drywall’s paper facing to disintegrate and turn mouldy. Even a tiny amount of water introduced through a crack or hole in the tile will expand once it hits the moisture-hungry paper facing and gypsum core of the drywall. Because paper is an organic product, it will quickly become mouldy.
- Greenboard: Greenboard’s acceptability as a shower backer board is debatable. Greenboard is only slightly more water-resistant than plain drywall. Green Board has drywall’s same gypsum core and a paper facing. However, the facing is impregnated with waxes that shed water better than conventional drywall’s paper. Many local building codes do allow for the green board as a tile substrate in showers. But with many non-organic shower backer boards available as alternatives, there is little reason to use the green board.
- Plywood: Plywood alone cannot be used as a substrate under tile in showers. Some homeowners believe that painting or priming plywood will render it suitable to use as shower/tub backer board. This is not true. Since plywood is often used as an underlayment for floor tile, some do-it-yourselfers may believe that it can also be used in shower wall applications.
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Mistakes To Avoid For A Waterproof Shower Floor
Assuming Grout, Tile And Sealers Alone Make A Waterproof Shower
Tile and sealed grout are water-resistant, but without the proper preparation and installation, water will find its way around them in no time.
- Take time to install the tile correctly. The Tile Council of North America Handbook has detailed instructions on how to prepare shower floor for tile and how to install for waterproof bathroom tile, including shower pans, waterproofing membranes, and backer board for the shower walls.
- Stick to the same manufacturer for as many components as you can. If you use a shower pan from one manufacturer and waterproofing from another, they may not be compatible.
- Double-check how much waterproofing or sealing is needed. One coat may not be enough.
Forgetting To Calculate The Proper Amount Of Slope For The Drain
Without the right slope on the floor of your shower, the water will not drain properly. Standing water is a recipe for growing bacteria and developing leaks.
- Ensure the shower floor has a ¼” per foot pre-slope (slope before application of any materials).
- Hire a contractor if you have any doubts about your abilities.
- Install pea gravel or spacers around the drain and weep holes to enable drainage.
Forgetting to Do A Flood Test Before Installing Tile
Once you have finished preparing the shower space and before you start installing tile, test out the water tightness. It only takes a hole the size of a pin about 20 minutes to start seeping. It’s much easier to address leaks in your shower pan before the tile goes down.
- Test for a full 24 hours.
- Plug the drain with a test plug, which plugs weep holes and the drain, fill the shower pan and check periodically.
- Establish that the drain is tight by filling the shower pan up to the top. Any drop in the water level may indicate a leak.
- Pull the plug and watch to see that the slope is sufficient and weep holes are clear.
Breaching The Waterproof Membrane
Once you’ve created a waterproof zone, be careful to protect it from any breach while you are tiling a shower.
- Never use nails or screws to attach cement boards to shower walls.
- Avoid using nails or screws to attach curbs or benches.
Selecting Improper Tile For The Shower
All tiles are rated for different purposes, so be sure you’ve picked tile that is appropriate for the shower. Note that tile for the shower floor is a separate rating from tile for the shower wall.
- Check the specs on your tile to make sure it is rated for wet applications.
- Select different tiles for the floor and walls of your shower or a single tile for both that is appropriate for the shower floor.
- Apply sealers to your tile and grout regularly to add to its water-resistance.
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Poor Mortar Coverage
It may seem like it’s extra work to get full and even coverage with the mortar, but never take shortcuts when tiling a shower. Any empty spaces behind the tile are opportunities for bacteria growth should any water get through.
- Avoid using “dot” or “back buttering” methods of applying mortar.
- Tile requires a minimum of 95% mortar coverage to work efficiently in wet applications.
- Large-format tiles especially need good mortar coverage.
Many of the bathroom remodelling projects we have completed over the years have been in homes that were only 5 to 15 years old. By far the most common problem I have encountered has been tile installed over drywall in shower/wet areas. This is the case so much of the time that when people tell me on the phone that they have tiles they can push in with their hands in the shower, or that the tiles are falling off the wall or seem ‘squishy’, I immediately get the image in my mind of the very common 4″ ceramic tiles installed over drywall. And in most cases, this is exactly what they have.
This method of tile installation is simply bad practice, yet it is by far the most common situation I see in bathrooms that we tear out. The reason this is such a common practice by new home builders and remodelers is only for one reason – it is cheap to do. There is no other benefit than cost.
Many of these installations have water damage in the wall, on the studs, wet drywall, spots of mould/mildew in the wall, ants, and water-loving bugs present in the wall (at least this is what we have found in many occasions). Another issue is that at the bottom of the tiled shower wall (where the shower base is caulked against the shower wall), there is an endless black discolouring of the caulking. Even if you re-caulk this joint, in just a few months the caulk discolours and turns black again. The problem is that water does seep through grout joints and gets the drywall damp. This constant wetness with repeated showers every day doesn’t allow anything ever to dry out. (Please also see the value of having a good quality Bathroom Exhaust Fan)
The bottom line is that drywall (and this includes moisture-resistant drywall) should never be used behind tile in wet areas (showers and tub-shower combinations). The preferred method is to use something like Hardi-Backer or concrete board. However, with these products it is important to correctly build in the proper vapour barrier as without a proper vapour barrier water vapour will migrate through the wall and under certain temperature conditions, the dew point (inside the wall assembly) causes condensing of this vapour inside the wall (on outside walls). Done correctly, these products will work just fine. I have seen too many installations in which Hardibacker and concrete board was used but with the improper techniques that did not follow the manufacturer recommendations and industry guidelines.
We prefer “Wedi Board” as a tile substrate in showers. The “blue board” insulation that makes up the core of Wedi Board provides a continuous layer of insulation. The benefit of this is that this closed cell insulation is 100% waterproof, but it also provides a “vapour stop” to keep water vapour from entering the wall cavity. This is especially important in a shower located on an outside wall but also helps even if the shower is on an inside wall. The beauty of this is that you could install Wedi Board in a shower and not tile the shower at all (not that you would do this) – and take showers for years with just the Wedi Board in place (no title) and you would have a 100% leakproof shower. This means that by tiling over the Wedi Board, you are simply providing an aesthetic look to the shower but not relying on the tile itself to do the waterproofing of the shower. The tile does add a layer of waterproofing protection, but the real heart of the system is in the Wedi Board behind the tile. Compare this to the common practice of tiling over drywall, and you get the idea that you have a different shower by using a product that is meant to function in the shower.
The Wedi Board/ Wedi Shower system includes special bonding agents (referred to as “wedi caulk” though is much more than caulk) that waterproofs the seams in the corners as well as the joints where the 3×5 board pieces join together. This binding of the pieces throughout the shower also helps keep the whole system acting as one unit behind the tile, helping to keep tile and grout from cracking.
No matter what type of drywall you choose, there are a few things to keep in mind before installation. First, tearing down old tile and drywall can be a messy process. Keep a window open to provide plenty of ventilation and wear the appropriate safety gear for the job. Second, the installation will likely take a few days to complete, which may or may not leave you without a shower for a day or two. Lastly, make sure to turn off any electrical outlets close by and turns off the water to avoid accidents.
While there are a number of different options when it comes to the type of board suitable for a shower wall, the one thing to keep in mind is moisture. Whatever type of board you use, there needs to be a waterproof barrier installed behind the tile. Not only will this keep water from ruining the backboard, but it will also ensure that the structure of the wall is not comprised. Furthermore, it is also a good idea to install another water barrier behind the drywall in order to keep water from damaging the structure of the wall. By following these simple steps, you can save both time and money, knowing that your wall is properly sealed.