Tile lippage is a contentious topic in the industry, which is influenced by a variety of factors, such as subsurface tolerance, grout joint width, warpage, patterns and edge treatments—just to name a few. Floor Covering Installer sat down with various manufacturers to learn more about this popular topic, as well as the methods and systems they recommend for a smooth installation.

Panelists featured include Dan Marvin, technical services director at MAPEI; Brett Fleury, product manager at USG Corp.; David Stowell, technical director at HPS Schönox; Nick D’Andrea, tile and stone marketing specialist at Ardex Americas; Noah Chitty, director of technical services at Crossville; and Michelle Swiniarski, market manager of ceramic systems at Bostik.

FCI: What systems do you recommend using for a smooth flooring installation?

Marvin: As tiles grow in size (and often shrink in thickness), substrate preparation becomes an increasingly important part of the overall installation. Installers of other floor coverings routinely use self-leveling and patching to bring substrates into tolerance before installation. This should also become standard practice for tile installers. By making sure floors meet the 1/8 inch in 10 ft. flatness requirement in ANSI, installers have already solved half of the issues that contribute to lippage.

Fleury: One of the most common contributors of tile lippage is the inconsistent application thickness of the thinset mortar below the tile. Troweling thinset over a rough or uneven substrate can be challenging as you progress from one end of the room to the other. Out-of-flat floors become even more problematic when installing large body tiles because the installer has to ensure every tile has a sufficient amount of mortar to fully support the tile. It is for this reason that every good tile installation begins with proper substrate surface preparation.
There are many ways to smooth or flatten an uneven substrate. Methods may include grinding or shot blasting the substrate, troweling out a quick-setting floor patch or troweling out thinset mortar the day before. There are positives and negatives to each one of these options depending on the severity of subfloor imperfections, size of the area that needs to be addressed, subfloor tolerances required by the tile manufacturer not to mention time and cost constraints.

For these reasons, the installation of a self-leveling underlayment (SLU) is the best way to achieve a very flat or level floor prior to tile installation. In years past, this option was very costly due to the amount of subfloor preparation required before the pour (shot blasting of the concrete or installing metal lath on a wood subfloor) and the amount of time the installer loses while waiting for the SLU to cure sufficiently.
Advancements in chemistry however now offer the tile contractor more cost effective SLU solutions to obtain a very flat surface. By formulating low-prep (prime and pour), fast-applying. engineered cement self-levelers, the amount of substrate preparation and downtime has been dramatically reduced, making the SLU solution more palatable. In most cases, pouring SLU’s to meet demanding floor flatness values is less labor intensive and easier than the aforementioned procedures.
Once installed, the newly prepared flat and smooth SLU surface allows the notches of the trowel to properly gauge an even and consistent amount of thinset across the floor which ultimately helps reduce or eliminate lippage as a result of inconsistent thin-set mortar applications.
There are still many other contributing factors to tile lippage (grout joint width, tile warpage, patterns and edge treatments) that may not be addressed by simply having a smooth flat floor. Hence the proliferation of many different tile leveling systems. If you are still encountering tile lippage issues, there are many products and procedures that can help you tackle the issue from the top down.

Stowell: Getting the substrate to meet standards becomes a dilemma with today’s large-format tile sizes. One of the most important methods to help prevent or minimize lippage issues during installation is to ensure you have an even substrate surface. How does an installer fix the floor so it is flat enough to receive tile? The solution is a self-leveling underlayment, which is designed to flatten or possibly level a floor surface prior to installing tile.
The floor surface must be properly prepared and primed with the manufacturer’s recommended product and allowed to dry. Failing to prime can cause the SLU to dry out too quickly. It also helps bind residual dust to improve bonding and helps protect the surface it’s going over.
It is also important to consider moisture mitigation. Schönox EPA is a two-part, epoxy-based moisture mitigation system suitable on porous, unheated concrete slabs to reduce moisture vapor emission rates from 100% RH or 25 lbs./1,000 square feet/24 hours to suitable levels before applying Schönox underlayments.
Many architectural plans and specifications require the floor be level. This is especially true for highly specialized medical and technical equipment that require a perfectly level floor. In this case, ensure diligence and careful attention to detail when applying the SLU so that, when done, the bubble of a spirit level or transit successfully indicates a truly level surface.

D’Andrea: Managing tile lippage throughout an installation is more of a process than the use of an individual product or two. We believe there is no single tool or method that will prevent lippage during the installation, however, there are some best practices to consider. For instance, selecting the right tile, incorporating proper substrate preparation techniques, selecting suitable setting materials, and following the tile manufacturers grout joint and pattern recommendations in addition to incorporating edge tuning clips should all be considered. While none of these components on its own will yield success, failing to identify and follow the process could compromise both the aesthetics and overall performance of the tile system. With that in mind, a successful lippage-free installation always starts with a flat, well bonded substrate. With the stringent substrate tolerances set by the Tile Council of North America (TCNA), specifically with large-format tile, substrate preparation is almost always required.
Ardex Liquid BackerBoard Self-Leveling Underlayment for Interior Wood and Concrete Subfloors is a self-leveling underlayment that can be used over a variety of flooring substrates including wood, existing tile, terrazzo, plywood and OSB. Ardex S 28 Microtec Rapid-Set, Rapid-Dry, Super-Format Tile and Uncoupling is a revolutionary large-format and “super format” tiling mortar formulated to be applied at a consistency that makes collapsing the mortar ridges more efficient thus, helping to bed the tiles more evenly while achieving maximum transfer of mortar.
In addition to substrate tolerances, the TCNA recommends large-format tile with an edge greater than 1 meter requires a lippage control system, however, it’s important to note that these clips are designed for minor adjustments of the tile and not a substitute for proper preparation, and tiling techniques. Understanding the challenges with large-format tile installation, Ardex has developed several products that provide extended working times and a fluid consistency that will allow easier compression. These mortars are best suited to complement the various types of lippage tuning systems currently on the market.
Another significant area that requires attention when managing lippage is the mortar mix and application. It’s important to make sure the mortar is mixed consistently from bucket to bucket, as the fluidity of the mortar will affect how the tiles compress. Equally important is the technique in applying the mortar. If there is a variation in the amount of mortar placed on the substrate and back of the tile, it will make setting the tile evenly with the adjacent tile more challenging, potentially compromising the installation. To help properly bed gauged porcelain tile and gauged porcelain tile panel/slab, the American National Standards Institute (ANSI) has introduced edge vibrating to the general tile installation method under ANSI A108.9. To complete the installation process, the new method calls out vibrating the tile edges with a palm sander in conjunction with lippage control systems. This is another reason how selecting a mortar with an extended open time and thixotropic properties can help support a lip free installation.

Chitty: For sub-surface tolerance, we recommend following the industry standards for floor flatness for the size tile you intend to use. In this respect, we really push people to become more knowledgeable on the options and how to use all of the great self-leveling and patching products that are out there. I would say the same for grout joint width, although we have discussed in committee some possible edits for those standards to make them better. For example, for porcelain on floors or pressed floor tiles, there is discussion of whether minimum grout joint of 1/16 inch should be increased to 1/8 inch, which will take some debate and further research. We are also working on improving the language for patterns to not just address 50% offset running bonds, but also for examples of 12 x 24-inch herringbone, which also puts the middle of one tile next to the corner of an adjacent tile. For edge treatments, I would just say use the right one and install it right; there are so many great solutions in this category to take advantage of. For warpage, I would of course say to use a quality tile from a quality manufacturer, but it is also important to understand the industry standards and that some classes of tile have tighter tolerances than others for things like warpage.

Swiniarski: The subject of tile lippage becomes an ever increasing discussion topic with the continued trend towards large and heavy format tile. Bostik recommends following all ANSI and TCNA guidelines for lippage as well as tile manufacturer’s guidelines for their specific tiles.
Minimizing lippage begins with ensuring the substrate is flat. The larger the tile, the more critical flatness becomes. The TCNA recommends a maximum of 1/4 inch in 10 feet subfloor flatness for tiles with edges shorter than 15 inches and 1/8 inch in 10 feet for tiles with at least one edge greater than 15 inches. Ensure substrates are within recommended tolerances or better. Reduce any high spots in the substrate and fill in any low spots. Bostik recommends the use of our self-leveling underlayments and patches to obtain the necessary flatness.
It is also important to establish realistic expectations with the customer prior to installation so they understand what to expect in their flooring appearance. It is important to have a conversation regarding the selection of tile and the amount of lighting in the area to be installed. Tiles with polished surfaces have a tendency to highlight lippage more than those with a matte finish. Lighting techniques are also important, as lighting can cast shadows and exaggerate lippage.
It is also important to understand the importance of the size of the grout joint. The more variation a tile possesses, the wider the grout joint should be to assist in reducing potential lippage. Always check with the tile manufacturer for their acceptable offset pattern. The tile installation pattern also plays an important role. Staggered tile pattern installations help to minimize the appearance of lippage as well.

FCI: Are there certain products/methods you use to prevent lippage?

Marvin: Self-levelers, patches and wall rendering products help provide a flat substrate. We have also seen a resurgence in interest in old-school mud bed floors and walls. A variety of lippage tuning devices are also on the market, and our experience has been positive with most of them. Make sure that the caps can be removed and replaced to clear away excess mortar before it has cured and that the straps can be removed cleanly without chipping the tile once cured.

One method we do not advocate is ‘five-spotting’ or ‘dotting’ mortar [also known as ‘spot bonding’] on the corners of the tile and then manually flattening it. This is the basis for many claims for debonding, and when we see it, we immediately know that the installer cut corners. Instead of five-spotting, use a large and heavy tile mortar designed for use with tiles larger than 15 inches on any side or more than 5 pounds per square foot in weight. Also, for large-format tiles over 15 inches on a side, do not use 50% offsets with the edge of one tile next to the middle of the tile next to it. This can make existing warpage in the tiles appear worse. An offset of no more than 33% is recommended for these tiles.

Fleury: When it comes to addressing lippage from the bottom up, USG offers a portfolio of products that can properly prepare a substrate for tile while simultaneously addressing time, cost and job site conditions. A few of the most notable products are as follows:
USG Durock Brand Quik-Cover Self-Leveling Underlayment requires no mechanical preparation for most installations over concrete and can be applied directly to wood at a 1/2-inch thickness without metal lath*. It is extremely fast setting and allows for the application of most floor-coverings including porcelain ceramic and natural stone in as little as 60 minutes. This fast-setting product eliminates the traditional prep, pour and wait self-leveling solutions ensuring minimal delay between floor preparation and tile installation.
If the installation can wait until the next day, USG Durock Brand Quik-Top Self-Leveling Underlayment can be poured from feather-edge up to 3 inches and is ready for tile in as little as 15 hours*. It has excellent flow characteristics which provide an ultra-smooth, bondable surface for tile applications.
And if a trowelable solution is preferred, USG Durock Brand Advanced Skim Coat Floor Patch doesn’t require a primer for most applications. It can be installed from a feather edge up to 1/2 inch and can be ready for tile in as little as 15 minutes depending on environmental conditions and thickness of the application.
*Substrates must be primed with USG Durock Brand Primer Sealer prior to application of the leveler.

Stowell: Schönox offers six different types of SLUs: Schönox US, Schönox ZM, Schönox ZM Rapid, Schönox DSP, Schönox AP and Schönox APF. Three critical factors in any SLU project:

1. Accurately measure the water for the mix. Too little water can impede the flow of the mixture while too much water can cause the aggregate to sink to the bottom, separating from the other components, yielding a weak and powdery surface.
2. Use a mixer that maintains the proper speed. If the speed of the mixer is too slow and/or not for the correct amount of time, the product will not be properly combined and may not function as specified.
3. Mix for the recommended time. Be sure to have enough help to mix, move, pour and smooth the product within the allotted time.

Once the SLU is poured onto the floor, move it into place with a gauge rake having adjustable legs to control the product thickness. When completed, move a surface smoothing tool across the surface to break surface tension and flatten the SLU. Allow the recommended dry time depending on the environmental conditions before installing tile.

Chitty: The only other thing I would say is that consistency of installation practices are important to reducing lippage. Things like measuring the water for thinset and making the same mix every time, holding the trowel at the same angle, controlling the absorption of the substrate can all help to reduce lippage problems. For the type of products described above [in the previous question], all of the setting material and edge profile manufacturers have great solutions and we don’t recommend one manufacturer over another.
The only place we make a manufacturer specific product recommendation is lippage control systems for our Laminam product (and really if asked what we would recommend for any tile) where it would be the MLT Lippage Tuning System. Our department is tasked with minimizing claims and we feel MLT is a better engineered system for both reducing lippage and mitigating any risks associated with using a lippage control system. The product was built for Laminam type products (thin tile) so for us it only make sense the same benefits would apply to traditional thickness tile. We do tell people that if they decide to use another system, especially with thinner tiles, that using the strap as a spacer (where the tile edge is in direct contact with something that will later be removed from the joint) and the removal method of kicking or hitting with a mallet, for us, increases the potential for chipping the edge of a tile and that steps should be taken if using other systems to mitigate those potential risks. The other benefits of MLT like a removable cap, a better-than-the-rest encapsulation of the plastic foot left under the tile, and the ability to pull straight up out of the joint when releasing the system via the removal tool we feel are enough benefits to recommend that system over others, which is something we normally try to stay away from.

Swiniarski: Bostik recommends using mortars specifically designed for large and heavy format tiles (LHT) when installing these tiles. These mortars are designed to support the size and weight of LHTs, and are designed to accommodate their warpage and to ensure continued contact with the tile when larger trowel notches are used. It is important to ensure that no one steps or leans on the tile while the mortar is setting as this may shift the tile and cause lippage as well. Many lippage control devices exist and are very helpful in ensuring the tiles stay as even as possible while the mortar is curing.