Shower Installation and Waterproofing: Tips & Common Errors

When it comes to waterproofing and shower pan liner installation, taking shortcuts can lead to disastrous results. This is especially true 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.  

Below we address six waterproofing and shower pan liner installation mistakes that heighten the probability of shower system failures. 

1. Inadequate structural support of subfloor  

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.

If you are a venturous do-it-yourselfer planning to waterproof your own shower, ensure you are well-versed in the steps you need to take. We recommend reviewing your local building codes, as there are many factors to consider.

Most importantly, when it comes to structural integrity, it's best to contact a professional to confirm that the subfloor is installed correctly and free of defects. This is especially important if you are repairing an older shower.

2. Using the wrong materials for drain-base installation  

Make sure to secure the drain base to the subfloor using the correct anchor. If it's wood, you'll want to use screws to secure the drain base. If it's concrete, use a masonry anchor.

While it may seem obvious, your drain base should match the material of your plumbing system. If you have ABS piping, use an ABS drain base. If you have PVC piping, use a PVC drain base, etc. Similarly, you'll want to use the right solvent cement to connect the drain base to your system.

Make sure to drill the proper size hole for the drain base being installed. For example, a 4-½-inch hole is recommended for Oatey tile shower drains. Refer to manufacturer instructions for proper sizing. 

3. 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 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 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.  

Another key consideration related to wallboard is to check with the manufacturer on the correct height above the mortar for the shower pan. 

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

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.  

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, 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.  

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.   

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.

Pre Shower Liner and Waterproofing

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.    

When you apply silicone caulk around the surface of the inner flange for the liner installation, be sure not to apply too much. Many installers tend to think more is better, but that's actually not true. If you apply too much silicone, there's nowhere for it all to go after you place the clamping collar. So, the excess silicone tends to bubble up under the liner and can block the weep holes.   

Oatey Tip: If you want to save time and hassle, install Oatey's Perfect Slope to the subfloor, making sure to trim the Perfect Slope to your shower dimensions, as well as around the drain, for a flush fit. Application videos and instructions are available at   

A complete shower solution is the best way to ensure effective drainage and prevent leakage. QuickDrain (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.  

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, this single pitch improves drainage, giving water one uniform path to the drain, and 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.  

QuickDrain Shower Pan

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

5. Improper shower pan liner installation 

Traditional shower floors incorporate a liner as a waterproof membrane between the pre-pitch and mortar bed.    

Be sure to apply silicone caulk around the surface of the inner flange when you assemble the drain base and install the shower pan liner. (But, as mentioned above, don't overdo it.)   

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 shower pan liner and then try to use pipe cement to bond it. Instead, shower pan liners should be folded in the corners. There's nothing wrong with measuring two or three times and making sure you have the correct measurements before you cut the liners — especially if you have only a certain amount of liner. 

Oatey Tip: Pre-fold the edges for easy application of the shower pan liner. Flip the liner over and mark it upwards from the edge according to the application height on three sides. Fold the sides at each mark.

For outside corners and curbs where it is necessary to cut the liner, we recommend using dam corners to waterproof these areas. PVC dam corners are pre-formed 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.

Prefolded shower pan liner

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. 

Oatey Tip: Add staples only to the top half inch of liner for maximum waterproof protection.

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

Dam corners being installed

It is important to follow 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.

6. 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.  

Flood testing shower pan

In conclusion: Aside from deterioration over time and failure 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.  

Also, check out our project guide: How to Install a Shower Pan Liner: Build a Waterproof Shower from the Ground Up. 

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