Shower Installation and Waterproofing: Tips & Common Errors


When it comes to shower installation and waterproofing, taking shortcuts can lead to disastrous results, especially when a floor is not properly sloped to the drain and/or a waterproofing membrane is carelessly installed. Professionals should know all the ins and outs of waterproofing systems, including what not to do.

At Oatey, we highly recommend installers and contractors follow all manufacturer instructions when installing a waterproof shower system.

Although there is a wide range of waterproofing membranes and accessories available, we strongly advise using one manufacturer's shower system to promote effective waterproofing and efficient drainage.

According to Building Connection, “waterproofing is one of the most complex trade issues and a major cause of residential building disputes due to failed or poorly installed waterproof membranes to shower recesses, balconies, rooftops, and other wet areas.”

But how can you prevent these issues from appearing in your shower installation projects?

This article addresses five different installation and waterproofing mistakes that heighten the probability of shower system failures.

1. Adequate Structural Support of Subfloor

Shower failures can stem from many different issues. First and foremost, when constructing a shower, whether you're using a pre-formed pan or a mortar bed, be sure that your subfloor is free of defects and meets all TCNA (The Tile Council of North America) standards. Any movement in the shower system because of an unstable substrate will most likely cause failure.  A waterproofing membrane is only effective if properly supported.

2. Waterproof vs. Water Resistant Wall Board

Another common issue is improper use of wallboard for the application.

Many installers use wallboards that are water durable, but not waterproof. A water durable (moisture resistant) material or product can withstand water penetration to some degree, but not entirely; whereas a waterproof material or product is impervious to water.

TCNA states, “A waterproof membrane or vapor retarder membrane must be specified to prevent moisture intrusion and protect adjacent building materials.” ~B412 Bathtub or shower with prefabricated receptor. Cement board or Fiber-cement board. Ceramic Tile.

Installing the correct kind of wall board 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 your shower system can help prevent water penetration.

In addition, if the board is not waterproof, water vapor and moisture will cause damage to surrounding structures causing mold and mildew growth. This damage can cause rotting of structural members leading to costly repairs.

3. Failure to protect weep holes and pre-sloping the floor before adding the waterproofing layer

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, PVC, CPE, hot mop, the subfloor below the liner must be counter pitched to a subdrain.

Mortar Bed

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.

Weep holes are a vital part of any shower system, whether using a traditional method or a topical waterproofed shower system. These weep holes are integrated into both clamp collar drains and most shower systems, such as QuickDrain USA shower systems.

Weep holes are important in any shower system to evacuate 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 weep holes do not get clogged.  Take care not to apply mortar or thinset to weep holes in your shower system. When installing the drain clamping ring, ensure the weep holes are clear of any residual pan liner or silicone.

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 the weep holes. In time, this over saturation causes deterioration of the thin-set below the tile or mortar bed. In addition, it can cause mold and mildew in the shower and create a foul odor or discoloration.

As mentioned earlier, a complete shower solution is the best way to ensure effective drainage and prevent leakage. QuickDrain USA ™  (part of the Oatey family of brands) linear or square drain systems include an integrated drain, pre-sloped shower pan and topical sheet or liquid waterproofing accessories.

QuickDrain Shower Pan Liner

Make sure all products in the installation work together as a complete system. Furthermore, some shower drain systems offer easier installation - for example, linear drains. Installers need to create a slope in only one direction, compared with a conventional four-way, compound slope used with center-point drains.

In addition, the single pitch improves drainage, giving water one uniform path to the drain, minimizing installation errors and hazardous standing-water "dead spots." Watch this video for step-by-step instructions on how to install a complete QuickDrain ShowerLine linear drain shower system.

QuickDrain PET Quick Slope panels, made of 100% sustainable products, affordably accommodate shower footprints between 26 to 72 inches, with an interlocking design that can be quickly and easily modified to any size or shape directly on-site. QuickDrain also provides complete membrane or liquid waterproofing kits.

Always follow manufacturer recommendations for mortar bed and liquid-applied waterproofing product applications.

4. Improper liner installation

Traditional shower floors incorporate a liner as a waterproof membrane between the pre-pitch and mortar bed. But, again, it is imperative that the liner not interfere with the drain's weep holes.

In addition, many installers incorrectly cut the corners of the liner and then try to use pipe cement to bond it. Instead, shower pan liners should be folded in the corners. However, for outside corners and curbs where it is necessary to cut the liner, we recommend using dam corners to waterproof these areas.

Oatey Shower Pan Liner

PVC dam corners are preformed corners designed to seal the junction of the curb and door jamb where a flexible liner membrane has been used for a traditional tiled shower installation. Use Oatey® X-15 bonding adhesive for PVC and Oatey Weld solvent cement for CPE material.

Penetrating the waterproof membrane or liner is another common error that can lead to shower failure. Water will migrate through any holes, reaching the framing and surfaces behind it. When attaching cement board to walls and curbs, do not use nails or screws lower than four inches above the flood rim or the top of your curb.

This video provides step-by-step instructions on how to install a shower pan liner.

It is important tofollow the manufacturer's installation instructions for all waterproofing products to ensure you have the proper water-tight coverage, especially topical liquid waterproofing, or elastomeric waterproofing. The use of a Wet MIL thickness gauge is recommended to ensure correct dry coverage has been achieved.

5. Failure to perform a flood test before installing tile and grout

Another critically required step to avoid issues with shower installation is flood testing. It is the best way to determine if you have a leak before installing your shower system.

A flood test can be done by inserting a pneumatic or mechanical test plug in the drain. Then fill the shower to just below the flood level or slightly below the curb. Oatey recommends a minimum testing time of four hours.

Check with local code jurisdiction for appropriate testing requirements. Then check for leaks, repair as necessary and retest the liner until the installation is leak-free.

In conclusion: Aside from deterioration over time and failing to flood-test showers before tile installation, most shower failures today are traditional mortar bed installations. Mortar installation allows more room for error and potential damage to the substrate, while newer pre-sloped pans eliminate common human errors in accomplishing the proper, 2% pitch. In addition, topical waterproofing (liquid or fabric) minimizes the water buildup that can degenerate the pre-slope below.

When in doubt or if you have any questions about installing Oatey shower systems, contact our Technical Application Team here.

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