When it comes to installations in wet areas, whether involving tile or stone, there are many precautions to take. A project’s longevity relies on a variety of factors, not just the products that are used—which is a common misconception among many installers.

To learn more about ensuring the success of any waterproofing application, Floor Covering Installer looked to more than a handful of industry professionals for their advice. Panelists include Duane Farley, M-D Pro’s national sales manager, Canada; Mark Albonetti, M-D Pro’s Prova technical specialist; Jarrod Persun, research and development engineer at Schluter-Systems; Steve Taylor, director of architecture and technical marketing at Custom Building Products; Art Mintie, senior technical services director at Laticrete; Tom Plaskota, technical support manager at H.B. Fuller Construction Products; Michelle Swiniarski, market manager of ceramic installation systems at Bostik, Inc.; and Tim McDonald, senior vice president of Merkrete.


Q: What are some common misconceptions about waterproofing products and common mistakes that installers might make working with the product?

Farley: I think the biggest misconception for waterproofing products is some products/backer boards are described as “waterproof” because water won’t change or deteriorate the material, but water will enter the board and eventually go through and into the wall cavity. When we talk about waterproof showers, we mean water will not penetrate the membrane or backer board. The most common mistake installers will make is using materials that are not meant for wet areas like mastic and pre-mixed mortars.

Albonetti: One misconception is that cementitious grout is waterproof. The conventional mud pan method is designed to take water that filters through the grout and mortar bed through weep holes in the drain assembly into the waste line. Any installer that has ever replaced an old mud pan knows that water can stay in the pan and the moisture can help create mold, mildew and an odor that can leave you breathless.

Taylor: Many installers believe that the installation of a waterproofing membrane is the same for all products and do not read the manufacturer’s installation instructions. Quite often, liquid-applied waterproofing membranes are applied at the wrong coverage rate or mil thickness. It may have been correct for one product, but not necessarily the one they are installing at the time.

We also see errors in seam treatment with sheet-applied waterproofing, which allows water to seep through between the sheets and undermine the assembly and the substrate. It is important to always review the manufacturer’s installation instructions prior to installing any waterproofing membrane. Pay careful attention to the recommendations for treating transitions and plumbing protrusions.

Mintie: A common misconception is that simply installing tile is enough to combat water intrusion issues. This is false, as water will always manage to find its way through the installation system. This is a typical mistake for a DIY installer.

There is also the misconception that all ceramic and porcelain tile installation materials are made waterproof. In reality, not all installation materials, including thin set mortars and grouts, are suitable for wet or submerged applications. The best way to guarantee a waterproof installation is by applying an ANSI A118.10 compliant waterproofing membrane, ensuring that the tile application is properly installed and indeed waterproof.

Plaskota: For waterproofing, there is a positive side and a negative side defined by the location of the water. Positive side waterproofing describes keeping the water from getting to the substrate. Examples of this are water on the surface of a kitchen floor or in a swimming pool.

Negative side waterproofing is the term for keeping water from coming in. An example of this is ground water below a concrete slab on or below grade. Waterproofing and crack isolation systems for tile installation are typically designed for positive side waterproofing only. These systems are not designed to be a barrier against water coming up from under the substrate.

Another less common misconception about waterproofing in general is that the tile, grout and mortar can provide a waterproof barrier. Of course, this is not true, and in wet areas waterproofing products should always be used. Not all waterproofing membranes are also vapor barriers. Wet areas that see a lot of moisture vapor transmission, such as a commercial showers or steam rooms, may need to have a vapor barrier in addition to waterproofing in order to avoid the risk of water collecting in an unwanted location. For example, in a wall tile installation, when the vapor moves through the tile assembly into a wall cavity and condenses into liquid water it can increase the chances of mold growth. This problem can be avoided with proper vapor barrier precautions.

Swiniarski: There is a common misconception that all waterproofing products are alike. It is important to understand the difference between products which prevent water vapors rising from the substrate and affecting the finished floor, and products that are meant to keep surface moisture from penetrating into surrounding areas such as the substrate.

Also, some individuals believe that all waterproofing products are adequate for use as both a negative or positive pressure membrane. Negative pressure in very basic terms is when the water penetrates from the opposite side of a substrate and tries to push the waterproofing product/membrane off from the substrate. Positive pressure is when pressure is exerted on the same side of the waterproofing product/membrane and pushes it towards the substrate. Vapor transmission is when water vapor passes through a substrate.

Common mistakes are not preparing the substrate properly, temperatures that are too hot or too cold during installation, not properly allowing the products to dry, applying liquid membranes too thin, not keeping other trades away from the installation area while the product is being applied and curing, or not flood testing the installation prior to putting it into service. It is also very important to ensure all of the products utilized in the system are compatible and are recommended for the intended use.

McDonald: One of the most misunderstood concepts about waterproofing under tile or stone is that all of them are equal. Not so. Liquid-applied, sheet goods, hot mop, and pre-fab all have their advantages and limitations.

For any application, it’s best to evaluate your specific project and choose the best product for that installation. Whether you are a first-timer or a 20-year veteran, liquid-applied membranes offer ease of application, monolithic safety with no seams to leak, and a 40-year track record of reliability in the workplace. Additionally, rapid-curing formulas are available today, which means same-day flood tests are possible in some cases.

When waterproofing under tile or stone, it is important to remember the basics: substrate, slope, drain assembly and application instructions. Waterproofing is one of the most critical installation steps a tile contractor is faced with. The liability can be huge. A leaking shower pan over a $20,000 piano is not something you want playing over and over again in your head.

To avoid leaks and ensure a proper installation, keep the following in mind:

  • For all applications under tile or stone, make certain that your subfloor meets the Tile Council of North America’s (TCNA) guidelines.
  • Check your slope and make sure it meets code requirements in your area. Typically, 1/4” per foot is a good rule of thumb.
  • Ensure all drains meet both the local code requirements and the specific manufacturer’s. Not all drains are designed for under tile membranes.
  • Not all membranes are installed the same way. There may be big differences between liquid-applied versus sheet goods. One of the biggest mistakes with liquid-applied membranes is that more will be better. A big build-up of ‘rubber’ in the corners or at the drain can cause a much longer cure time and a possible failed flood test.
  • Make sure your fabric (if required) is wrinkle-free. A wrinkle in the fabric even after cure can create a “tunnel” for water to travel after the membrane is dry. Allow your membrane, if liquid, to cure 100% prior to flood test.


Q: How important is flood testing?

Farley: Flood testing is very important to ensure the system was installed correctly. If a problem is detected, it can be repaired relatively inexpensively prior to the shower being finished with tile and glass doors systems.

Albonetti: Flood testing is important. Why go through the process of waterproofing a shower pan if you don’t test? Time is always a factor in any installation, but taking time—up to 48 hours or more—to test for leaks in the system could result in time and money savings. The time to find out is before finishes are completed and the cost of repairing or replacing can prove very expensive.

Persun: Performing a flood test after the waterproofing application is complete is a code requirement in many jurisdictions so this makes it inherently important. But it is also very important for practical reasons. It can be a reliable way to find any mistakes or damage from other trades that result in leaks before setting the tile. Repairing problems is a lot easier and much less expensive before the tiles are installed. Also, the tiles might temporarily mask a problem that will end up being much bigger and more expensive than it needs to be, so better to catch it early and make an easy repair.

Taylor: The building code in many communities requires flood testing in showers and other wet areas. It is always wise to flood test the waterproofing before the tile is installed. If the waterproofing membrane is not protecting the space below, it is best to find out before facing a costly remove and replace operation—plus potential damage. If the flood test fails, in the most cases the waterproofing membrane can be repaired and tested again before the installation of the tile. This saves the contractor time and money in the long run.

Mintie: Flood testing is the easiest and best way to validate whether an installation is truly waterproof. This is an especially important step for submerged applications such as showers, spas and pools. In addition to the costly repairs involved with water leaks, if an installation is not watertight, mold and other serious moisture issues could arise.

In many cases, flood testing of the membrane is recommended by the TCNA and may be required by applicable plumbing codes. To ensure your installation is up to code, a trained expert such as a technical service representative from your waterproofing membrane manufacturer can guide you through the process. They will be able to provide instructions on proper membrane applications, cure periods and flood testing protocol to help you avoid any expensive corrective work down the road.

Plaskota: Flood testing is a critical step to verify that the waterproofing membrane is working properly. Installers must follow the manufacturers’ directions for drying time of the membrane and then test it to make sure it does not leak. Flood testing a wet area will identify both pinhole or transition leaks before tile is installed. The leaks can then be fixed with additional coating. Skipping the flood test can lead to very costly removal of the entire tile installation to find where a leak is located. For critical watertight installations, this step should never be skipped.

Swiniarski: Flood testing is the only sure means of ensuring that the installation will perform as expected once the installation is put into service. It is very costly in time and money should you put an installation into service only to discover your waterproofing has a breach. Water damage can be extensive not only to repair the existing area, but also to repair surrounding areas.

McDonald: In my 40-plus years as a manufacturer of waterproof membranes, I have witnessed many failures where the tile or stone was installed over an improperly applied membrane. The result was wasted time and money on removing a beautifully crafted installation just to fix a one-dollar mistake or a one-inch missed applied area of fabric. It’s worth the extra time to check.


Q: Are there any other steps installers/contractors can take to ensure a waterproof installation?

Farley: Use proper materials as recommended by the manufacturer during the entire installation process. Don’t use different waterproofing materials together unless recommended by the manufacturer.

Albonetti: Always use the best products and read and follow the manufacturer’s recommendations. Waterproofing is water management.

Persun: More important than any single tip or pointer is to select a complete system and follow through on all the details. There are different methods and products that work, as can be found in the TCNA Handbook for Ceramic, Glass, and Stone Tile Installation and various manufacturers’ technical literature, but every requirement in these methods must be respected to ensure success (and qualify for the manufacturer’s warranty). Read and understand the instructions and ask questions as needed. Also, take advantage of education and training opportunities.

For example, Schluter-Systems has an entire series of installation videos on our website and YouTube, and we run training sessions and workshops for professional installers regularly.

Taylor: Proper surface preparation and drainage are both important for successful waterproofing. It is critical that the substrate is properly pitched to the drain without any birdbaths that could collect water. Many times we see the tiled floor pitched in the wrong direction, allowing water to sit on the surface of the tile. This can saturate the assembly, becoming an aesthetic or health issue and even creating a slip and fall hazard.

It is also important that the surface is properly prepared to accept the bond of the waterproofing membrane. If the membrane is not well-bonded and comes loose, it will be ineffective in controlling water, leading to substrate damage. For the most durable and reliable results, select a third-party tested membrane that exceeds ANSI A118.10, such as RedGard Waterproofing and Crack Prevention Membrane.

Mintie: It is critical for contractors and installers to create a complete “pan effect” or “waterproof envelope” to properly contain water and prevent leaking. This is achieved by applying waterproofing membrane beyond the area that is designated to contain water.

If showers, tubs or pools are not properly waterproofed, water will seep behind the tile installation and inevitably manifest into a leak and lead to costly repairs. By using a complete installation system such as the Laticrete Hydro Ban Shower System, the installer can ensure full warranty coverage and complete product compatibility.

Plaskota: As is the case with any applied coating or membrane, proper substrate preparation is a critical step to ensuring that a flooring installation is waterproof. The substrate must be clean and sound before the installation starts. Dirt will keep waterproofing membranes from bonding properly to the substrate.

Another important action for ensuring a waterproof surface is to make sure to allow the manufacturer-recommended dry time for the film formation. Installing tile too soon over a wet waterproof membrane can lead to a tile bonding issue that cannot be resolved without removing the tile. Installers must patch or smooth the substrate before the waterproofing membrane is applied. The substrate must be smooth for a quality tile flooring installation.

It is also important to make sure that you have suitable substrate construction. For wood frame floor substrates, verify that the plywood subfloor and underlayment are the right thickness and joist spacing is appropriate to support the flooring. Check the substrate construction carefully before starting the waterproofing application.

Swiniarski: It is critical to take the time to properly prepare the substrate. Read and follow all installation instructions and industry standards. Ensure the product, substrate and jobsite conditions are within the recommended tolerances for temperature and humidity. If a question arises and you are unsure how to proceed, take the time to stop and call the manufacturer to obtain technical assistance. Ensure you are obtaining the correct coverage for the product. Allow the product to dry properly and protect it from other trades during installation. Flood test the installation prior to putting it into service.

McDonald: Waterproofing is the single most important product you will install as a tile contractor. Nothing you do has more liability or is more costly to repair if done incorrectly.

If you are completing your first waterproofing project, seek assistance. Almost all manufacturers of waterproof assemblies have technical representatives to assist with the entire installation process. Don’t be shy; proper application requires sound waterproofing principles. The smallest mistake or missed step can create a nightmare and lost profit.

Some recommendations:

  • Check the subfloor. Is it sound? Does it meet TCNA requirements for waterproofing?
  • Ensure proper slope. The key to successful waterproofing is making sure the water runs off the membrane as quickly as possible.
  • Ensure your drain is the correct one that meets local plumbing codes and the manufacturer’s requirements. If not, be sure by calling your manufacturer for assistance.