Installing the correct type of wallboard behind the tile is important, especially considering all the moisture the wall will have to endure over time. Inevitably, steam and water will penetrate through grout joints and porous tile materials. Routine sealing of a shower system will help minimize water penetration.
In addition, if the board is not waterproof, water vapour and moisture will cause damage to surrounding structures through mould and mildew growth. This damage can cause rotting of structural members and costly repairs.
Failure to protect weep holes
The most important part of any tiled shower system is the evacuation of weep water (i.e. water that collects below the tile). For a traditional liner install, polyvinyl chloride (PVC), chlorinated polyethylene (CPE), or hot-mop, the subfloor below the liner must be counter pitched to a subdrain.
This sloped mortar bed will be flush with the top edge of the two-piece clamp collar base which will allow the weep water to flow freely to the integrated weep holes.
Whether it is a traditional or topical waterproofed system, weep holes are a vital part of any shower system, and they integrate into clamp collar drains as well.
Weep holes also play an important role in evacuating water wicking through the grout or cracks between the horizontal and vertical wall transitions. Installers can utilize weep guards or pea gravel around the drain barrel to ensure the holes do not get clogged. To avoid closing off the drainage, installers should not apply mortar or thin-set to weep holes. When installing the drain clamping ring, ensure the holes are clear of any residual pan liner or silicone. TCNA B414 requirements state, “surround drain with pea gravel or other weep protection to prevent mortar from blocking weep holes.”
Pre-sloping before waterproofing
Many installers make the mistake of not pre-sloping before installing the waterproofing layer or leaving the weep holes in the drain base unprotected, resulting in water’s inability to evacuate through them. This over saturation, in time, causes deterioration of the thin-set below the tile or mortar bed. Likewise, it can also cause mould and mildew in the shower, creating a foul odour and discolouration.
All products in the installation work must together as a complete system. Some shower drain systems offer easier installation, for example, a linear drain requires a slope in only one direction, compared to a conventional four-way compound slope, which requires multiple centre-point drains. The single pitch of a linear drain improves drainage because it gives water one uniform path to the drain, minimizing installation errors and hazardous standing water (which can leave stains). Installers must always follow manufacturer recommendations for mortar bed and liquid-applied waterproofing product applications.
Improper liner installation
The National Plumbing Code of Canada (NPC), A-7.2.2.3 showers states, “the use of leak proofing materials such as lead sheet, rubber or plastic membrane, and polyethylene sheet with fleece webbing must cover the entire interior area. The leak proofing material must extend up enclosing walls above the height of the waste opening or the enclosing step by at least 100 mm [3.9 in.].”
Many of the shower receptor details in TCNA B412 note how waterproof membranes used in the installation of tile must meet the requirements of the American National Standards Institute (ANSI). ANSI A118.10, Load Bearing, Bonded, Waterproof Membranes for Thin-set Ceramic Tile and Dimension Stone Installation, specifies the requirements for a “load bearing, bonded, waterproofing membrane for thin-set tile and dimension.” The requirements apply to “trowel applied, liquid and sheet membranes.” This standard prescribes requirements to assure the membrane is waterproof and has the strength to hold up overtime.
Traditional shower floors incorporate a liner as a waterproof membrane between the pre-pitch and mortar bed. Once again, it is imperative for the liner to not interfere with the drain’s weep holes to ensure unimpeded drainage.
Many installers incorrectly cut the corners of the liner and then try to use pipe cement to bond it. TCNA and manufacturer instructions are to fold the shower pan liners in the corners. However, when it is necessary to cut the liner such as for outside corners and curbs, best practices suggest using dam corners to waterproof these areas.
