Tile showers are an amenity to any residence, and when constructed properly, can provide generations of reliable service. While a tile shower may appear simple on the surface, there is a lot going on behind the scenes. In fact, a tile shower can be one of the most complex assemblies a tile installer will ever build, which is why qualified labor is so important. This article will take a close look at one common shower type and many of the points that define its successful installation.
When it comes to tile showers, there is no standard design. Rather, there are varying methodologies and materials. A few of the many variables in showers include the following:
- Is the water directed to a conventional drain with weep holes via a “water in, water out” approach or to a flanged drain via a single line of defense approach?
- Is the slope to drain provided by a mortar bed or a prefabricated “pre-slope” mechanism?
- Is the slope in four directions to a centrally located drain or in one direction to a linear drain?
- Does the shower have a curb at the front to contain the water or is it curbless for wheelchair accessibility?
- Does the waterproofing take the form of a sheet pan liner or a liquid? Is it sandwiched between the pre-slope and the finish mortar bed or it is topical (i.e. bonded to the top of the finish mortar bed)?
- Is the bottom of the backer board on the shower walls buried in the mortar bed or it is elevated above the top of the mortar bed?
A few commonly specified shower assemblies that address each of these variables appear in the TCNA Handbook for Ceramic, Glass, and Stone Tile Installation, but there are also many variations of successful showers that do not appear in the Handbook. A qualified tile setter should be able to install any type of shower to exacting performance criteria. While a comprehensive analysis of shower receptors is out of this article’s scope, it will examine one specific shower, the TCNA B415 shower¹, and this shower’s critical points of design and installation. The B415 shower is currently one of three shower types that form the basis of the tile industry’s Advanced Certification for Tile Installers (ACT)².
Installation of Pre-Slope
A shower’s ability to direct water to the drain relies on the slope of the finish tile. The pre-slope sets the slope of the entire shower assembly, so it is critical that it be accurate. The pre-slope must have a uniform slope of ¹/₄ inch per foot (20 mm per meter) (2% slope) to the drain. A prefabricated pre-slope device simplifies this task, but if a mortar bed pre-slope is floated, it must have the correct and consistent slope without even slight humps or valleys that could impede flow, and it should be bonded to the substrate with modified thinset mortar or a cement slurry.
Installation of Membrane
The sheet membrane, also known as the shower pan liner or waterproofing membrane, is the component in the assembly that protects the substrate from contact with water. In the B415 shower, it is loose laid and continuous.
The membrane must be installed seamlessly inside the receptor, returning vertically up the perimeter walls to the distance specified. If separate pieces of membrane are required to create the vertical returns, the membrane must be adequately lapped and sealed. If the membrane is folded at the inside corners to avoid seams, the folds should be consistent at each corner to achieve a square angle once the backer board is installed on the walls. Folding the membrane at corners sometimes creates an excessively thick condition that may need to be corrected with shims at the time the backer board is installed. The membrane is mechanically fastened to the vertical framing or blocking, with the fasteners no lower than 3 inches (76 mm) from the top of the finished curb.
The membrane must be sealed to the drain collar with an approved sealant rather than simply laid loose to prevent water from becoming redirected underneath the membrane where it may never reach the drain. Once this task is complete, the drain’s clamping ring is installed, providing the critical watertight connection between the membrane and the drain.
The membrane must completely cover the rough curb, including the entire front face of the curb. There should be no fasteners on the top or inside surface of the curb. Installers must use preformed membrane corner pieces to ensure continuity at the top ends of the curb.
After the installation of the membrane (including all transitions and terminations) and weep hole protection, the in-progress shower receptor should be flood tested to ensure water tightness. Methods of flood testing vary, but they are generally based on ANSI D59574. This test method calls for the shower drain to be temporarily plugged and the shower receptor filled with approximately 1 inch (25 mm) of water and allowed to stand for one to two hours. The assembly is considered to have passed the flood test if no leaks are determined to have occurred during the test period.
Installation of Vapor Retarder and Backer Board
Although these components don’t always fall in the scope of the tilework, qualified tile installers should be versed in installing vapor retarder and backer board since these tasks may occur as the shower assembly is constructed and their construction often defaults to the tile trade.
When a vapor barrier is specified, it should be free of rips and tears, shingled over the shower pan liner and adequately fastened to the backing, but with no fasteners lower than 3 inches (76 mm) above the top of the finish curb.
The backer board is installed over the vapor barrier, or if there is no vapor barrier, it is installed directly over the pan liner using shims if necessary to maintain plumbness and then mechanically fastened to the framing. If the backer board is a cementitious backer unit (CBU) conforming to ASTM C1325, it may be buried in the finish mortar bed. Alternatively, if a more moisture-sensitive backer board is used such as fiber-cement backer board (ASTM C1278, ASTM C1288), coated or uncoated glass mat, water-resistant gypsum board (ASTM C1178, ASTM C1658) or cementitious-coated extruded foam board (ASTM C578), the backer board should be elevated above the top of the mortar bed so it does not absorb moisture through its bottom edge. In all cases, as with the pan liner and the vapor barrier, the backer board should have no fasteners lower than 3 inches (76 mm) above the top of the finish curb.
Installation of Weep Hole Protector
Every qualified installer knows that when using a conventional, two-stage drain, they must provide protection for the drain’s weep holes. A weep hole protector prevents the weep holes in the drain from becoming clogged with mortar or debris. Keeping the weep holes unobstructed allows them to function as a secondary method of handling any moisture that penetrates the tile surface and is otherwise unable to reach the drain via conventional channeling.
Installation of Mortar Bed and Curb
The final step of a B415 shower, before laying the tile itself, is the application of the mortar bed and the mud curb. These activities are typically done at the same time.
Because the installers have already formed the slope, the final mortar bed is floated to a consistent thickness and follows the contours of the pre-slope below. The mortar bed should retain the ¹/₄ inch per foot (20 mm per meter) (2%) slope and should be free of humps or valleys that could impede flow of water to the drain.
As the shower receptor is floated, mortar is also applied to the rough curb with metal lath reinforcement embedded. At its completion, the mud-finished curb should be square to the shower, parallel to the back wall, flat in the long direction and have a cross slope of ¹/₈ inch (3 mm) toward the shower. Once the shower’s wall, floor and curb substrates are in place, the final stage of installation is tiling and grouting the entire assembly.
Shower receptors are indeed complex assemblies and require extensive knowledge and many diverse skills even prior to installing the tile finish. Each of the skills required of a B415 shower, as well as most other common shower types, are taught by the International Masonry Industry Traning and Education Foundation (IMTEF) and joint apprenticeship and training committees. Additionally, the Tile Contractors’ Association of America’s (TCAA) Trowel of Excellence certification established credentials for best practice tile contractors who are signatory with the International Union of Bricklayers and Allied Craftworkers (IUBAC). For tile installers who aspire to be the most technically proficient in their field, the ACT assesses and certifies installers in seven critical skill areas, including shower receptors. Each of these qualified labor training and certification programs works closely with manufacturers of tile and setting materials to ensure that the union labor force is constantly kept up to date with the latest material, installation technologies and ANSI standards. Design professionals can ensure qualified labor on their projects by making one or more of these credentials a requirement in their specifications.
- Tile Council of North America Shower (TCNA) Method B415 Shower receptor: wood or metal studs, cement backer board or fiber-cement backer board wall, mortar bed floor, ceramic tile or glass tile.
- The ACT is an industry-wide certification program developed by TCNA and their manufacturer members, TCAA, IMI, IUBAC, National Tile Contractors Association (NTCA) and Ceramic Tile Education Foundation (CTEF). Visit www.tilecertifications.com for more information.