Tiling over tile


Is there anywhere besides TR711, TR712, and TR713 that discusses tiling over tile? I’ve looked on the TCNA website, which states that procedures are described “in detail” in those standards. Other than stating the existing installation must be sound, well bonded, and without structural cracks, there aren’t any real details. Are there differences between a concrete substrate and a wood subfloor? Do I have to determine HOW the previous installation is adhered and how much it weighs? What other things may I need to take into consideration that I wouldn’t otherwise?


The “TR”/Renovation methods in the TCNA Handbook for Ceramic, Glass and Stone Tile Installation are the methods that discuss tiling over an existing tile installation.

In addition, the 2018/2019 edition of the NTCA Reference Manual section “Tile Over Other Surfaces” (page 257) includes more information, such as the need to prep the tile surface by scarification or application of specialized primers to promote bond to the existing tile surface.

As you have sensed, it is critical that you thoroughly analyze the components of the existing tile installation to determine whether it was properly installed and whether it will serve as a quality substrate for the new Employee-Handbook-v9 installation you are looking to bond to it. Since all components of the existing installation will become the new substrate, it must be carefully analyzed to determine if it will successfully support the new tile installation. The Substrate Requirements section of the TCNA Handbook (pages 30 – 33 of the 2019 edition) are worth reviewing.

It may be necessary to remove some tiles, bond coat, and any underlayment to ensure they were correctly installed. Sometimes, drilling a series of core samples is a good way to determine the adequacy of the existing installation and how well it will serve as a substrate for your new tile installation.

You (or a structural engineer or similar) must ensure that the structure will be able to support the added weight of the new tile and bond coat over the existing installation. Deflection, live loads, dead loads, etc., are part of the consideration. TCNA Handbook methods for floor installations list the Service Rating for the method. Also refer to the Performance Level Requirement Guide and Selection Table in the 2019 TCNA Handbook (page 43) for more information on Service Ratings.

If the tile over tile is to be done in a wet area, you must take into consideration such factors as the type and condition of the existing waterproofing membrane, whether 95% mortar coverage was achieved in the original installation, etc. You will likely need to apply a new membrane before installing your tile. Doing this will encapsulate the existing tile and bond coat between two layers of membrane. It is important to determine whether adequate bond coat existed in the first installation to ensure no pockets of water or other materials are being trapped between the membrane layers.

As with tiling over any substrate, it is necessary to ensure the substrate meets the flatness requirement for the size of tile you are installing. If the existing installation does not meet the flatness criteria, it must be flattened with the appropriate materials first. Your setting material manufacturer can assist you with the correct materials (possibly including primers) and techniques to correct unflat substrates.

In summary, everything about the existing substrate and substructure must be considered before tiling over an existing tile installation. 

Should I grout the old fashioned way with mud cement?


I am looking for an opinion. I have installed a 4˝x8˝ porcelain outdoors with thinset with 1/4˝ joint. I wanted to grout the old fashioned way with our mud cement – with extra Portland – cleaned with sawdust. I feel that the joints were full years ago. Thank you so much, I look forward to your opinion.


While the system of grout you described may work well, depending on your ratio of materials, many of the modern grouts available today have been engineered to stand up to harsh climates and use.

Reading and following manufacturers’ instructions carefully, along with a little practice, will produce full joints and great results with today’s materials. I suggest checking with the setting material company that makes the thinset you’ll be using for their suggestions of grout for your installation.

Regardless which grout system you use, an exterior installation has many critical elements that must be addressed. Please refer to the Tile Council of North America Handbook For Ceramic, Glass and Stone Tile Installation for the appropriate method, details and materials for this installation. 

Should this be a demo or can I replace the shower pan?


I have a customer that has a shower stall they would like updated…a little. New custom glass enclosure, new fixtures, and…a new pan? The two walls of the shower are white quartzite. She is in love with it and does NOT want to remove it. However, the pan is fiberglass. She does not like it and it has stains that won’t go away. She would like to have some kind of stone or tile to replace the pan.

My questions: 

  1. Will I be able to make a pan that won’t fail in years to come?  
  2. I would expect that the fiberglass pan has a flange that wraps up behind the slabs of quartzite. If so, how do I address that


Thanks for getting in touch with us about this problem. Let me address your questions first:

1. Many shower pans have been made from tile and related components that, when properly constructed, last for a very long time. There are many methods to construct such a pan. Have you built a shower pan before? Which method or system do you use or are you familiar with?

2. You are correct that the existing pan likely has a lip that extends behind the first course of tile and possibly behind the substrate. As your question suggests, it would likely not be an easy or simple task to remove the band of the quartzite, patch or install the waterproofing membrane that may or may not be behind it, and replace the membrane and the quartzite and the pan with a new tile system that you will be comfortable with installing and selling to the owner as a functional system that will stand the test of time.

I suggest you determine the best method and system approach that you are comfortable with, and then discuss with the owner the reasons why it makes much more sense to demo, replace and upgrade the entire shower.

I look forward to hearing back from you so I can help guide you on the best way to continue. 

If a shower floor slope is 1/4″ per foot are other horizontal surfaces also 1/4” per foot?


I have a quick question about how much slope a shower bench or shower dry-off area should have.

The TCNA Handbook states that “All horizontal surfaces, for example shower seats, sills, curbs, etc., must slope towards drain.”

Shower floor slope is 1/4″ per foot. Are the other horizontal surfaces (bench, etc.) also supposed to be 1/4” per foot?


Yes, the correct slope for all horizontal surfaces is 1/4″ vertical (minimum) up to 1/2″ (maximum) for every 12” of horizontal run. 

– Mark Heinlein,
NTCA Training Director

Is there anything in writing regarding use of red body ceramic tiles as shower floors?


Image courtesy of Bedrosians Tile & Stone.

Is there anything in writing you can provide regarding use of red body ceramic tiles as shower floors? I generally don’t recommend high water-absorption products in showers. I realize the glazes are impervious, but I have seen failures when the body of the tile has a high water absorption >7% and in some cases >10%. Is this addressed anywhere in the NTCA guide either for or against it?


I discussed this with several members of our technical team. As you and I also discussed on the phone, we are not aware of any item in the industry standards, including ANSI A137.1, ANSI A108, the methods and best practices found in the TCNA Handbook or the NTCA Reference Manual that describe whether it may be acceptable to install a red-bodied ceramic tile in a wet area such as a shower floor.

The best basis we have to go on is whether this is a floor tile and whether the manufacturer recommends it for installation on floors in wet areas.

Also, it may be important to consider whether the type of shower pan this entry-level-option shower floor tile will be installed on is water-in / water-out (thick-bed system with a liner and pre-slope i.e TCNA Handbook Method B-415) or if the tile will be installed on top of a sloped pan with a surface-applied membrane. If it will be installed on top of a surface-applied membrane, it is important to
consider whether the draining water may be absorbed by the body of the tile as it percolates through the grout and into the bond coat and body of the tile as it makes its way to the surface-applied waterproofing layer. I do not know for certain if this will lead to an issue with bond or performance of the tile or of the system.

I ran your question past a Recognized Consultant for a quick opinion. Here is the slightly paraphrased answer: “In a perfect world, it would work, but I wouldn’t do it. Soft absorbent body, unforgiving of installation error, glazed surface. I don’t see any cost savings. Why not a cheap porcelain? Wet is one thing; soaking absorbent tile in soapy water is another.” 

– Mark Heinlein,
NTCA Training Director

Needing information about certification for thin porcelain slabs


I’m a tile contractor, and need information about certification for thin porcelain slabs. Please
contact me.


Please visit our website to view the locations we have scheduled for GPTP training in 2019.

Please note that some of the programs listed at this link are Substrate Prep / LFT classes. The GPTP classes are scheduled for:

  • Louisville, KY
  • Plymouth, MN
  • Denver, CO
  • Bethany, CT
  • Seattle, WA
  • Norcross, GA

Since these courses are in high demand, I suggest registering early. There is no fee to attend these classes, however $50.00 is charged at registration to hold your seat. The $50 is refunded when you attend. 

– Mark Heinlein,
NTCA Training Director

Tile over elevated deck with uneven concrete slab


I have an outdoor elevated deck approximately 300 sq. ft.

We removed the existing ceramic tile to reveal a very rough and uneven aggregate concrete slab. This slab also seems to have sunk in the middle a bit. 

The client wants us to waterproof with a waterproofing membrane system including a liquid-applied membrane, and then install porcelain tiles about 3/8” thick. 

Since the slab is pitched away from the house and is not level, should we try using self-leveling material? Skim coat? Apply the membrane and tile all in one step?  

Please advise. Thank you!


Exterior decks, especially those over occupied spaces, are very prone to failure and must be constructed correctly.

As you noted, the first concern on this project is the suitability of the concrete substrate. It sounds like the existing slab may be a candidate for repair with an appropriate topping coat or possibly with deck mud. But your description of its overall condition and that it has sunken in the middle might indicate that the original slab pour might not have been done correctly and the supporting structure may not have been able to properly support it. These existing conditions would translate into trouble when it comes to supporting the new tile system installation.

It is critical that any exterior tile installation, especially those attached to buildings, be sloped or pitched away from the building. The pitch must be at least 1/4” vertical fall for every 12” horizontal run. You want to make the planes to be tiled flat, but you would not want to make them level by placing a self leveler or any patch materials.

IF all of the supporting structure is correct and adequate and IF the slab is sufficient to support the new installation, then the deck system can be considered. TCNA Handbook Methods 103B and 104B would most accurately reflect the details required for the situation you are looking at. Please take a look at these in your Handbook and review them closely. Supporting structure, pitch away from the structure, waterproofing membranes, proper flashing to the structure, water runoff management systems, etc. are some of the critical points that must be considered.

It sounds like this may be a situation where the existing concrete should be removed and the supporting structure carefully analyzed. A method such as F105 could then be considered as a possibility for this installation.

The freeze-thaw environment in New York is an extremely important consideration for any exterior installation. Proper placement and construction of movement joints (and again, water drainage) is absolutely critical for the performance of the system. Even with proper materials, ongoing routing maintenance of the movement joints will be necessary.

There are far too many details to discuss in this email. Please take a look at the methods I’ve mentioned and compare them to the existing installation and what it will take to make the new installation conform to the methods.

Some material manufacturers make drainage mat systems that work well to manage the water flow and support the tile installation. After reading the methods and considering the points I’ve described please email back and let me know what approach you think might work best, and I can try to help you answer any questions you might still have. I hope this helps! 

– Mark Heinlein, 

NTCA Training Director

Why do manufacturers require a 33% offset brick pattern?


Greetings! I was wondering if you could solve a mystery for me. On numerous jobs, for both walls and floors, we are asked by interior designers to install 12 x 24 or similar tiles in a standard brick aka 50% offset pattern. However, for many of these, printed on the box of tile or stated on the order sheet by the distributor, it clearly states in one way or another, “Brick joint pattern to be offset 33%.” When we point this out, the designer doesn’t care and won’t approve a mockup (because they don’t want to order any extra tile). Most of the time the 50% offset on the floor doesn’t end up becoming a lippage or shadowing problem, though we also use a leveling system so perhaps that helps mitigate it. On walls, however, especially depending on the lighting, it can be a real problem.

I would like to know why manufacturers recommend this if it often isn’t followed (I see plenty of tile jobs installed with the 50% offset)? And why do most of the distributors display the tile on a display board with 50% offset if the manufacturer requests a 33% offset? Is everyone just trying to cover their butts on potential lippage and/or shadowing issues? And since tile setters are “the experts,” not designers or customers, is a mockup the only true way to relieve yourself of culpability if shadowing and lippage do result from disregarding a manufacturer’s recommendations?


Thanks for getting in touch and thanks for asking an excellent question.

At Coverings ’19, NTCA Training Director Mark Heinlein presented a demo about wall wash lighting and lippage, citing information from the ANSI standard, as two teams installed wall tile.

It is my guess that the designers you are working with may not be familiar with the requirements of tile industry standards and the reason why those standards exist and why manufacturers require certain offsets for tiles they produce.

Listed below are the tile industry installation standards that relate to this discussion:

  • ANSI A108.02 section 4.3.7 – Lippage – Guidelines, Explanation, and Caution
  • ANSI A108.02 section 4.3.8 – Grout Joint Size
  • ANSI A108.02 section – Running Bond / Brick Joint Patterns
  • ANSI A108.02 section Running Bond / Brick Joint and Any Offset Pattern (for your convenience, I have quoted this section here): 

As you can see, ANSI A108.02 is very clear. When this requirement is followed along with installing tile that meets the manufacturing standards of ANSI A137.1 and when the substrate flatness standard for tiles with at least one edge 15” or longer is applied, the correct mortar is selected and mixed properly, the correct trowel is selected and used properly by an adequately trained and skilled installer, a successful finished installation should occur. (Note: the substrate flatness requirement for a 12” x 24” tile only allows a maximum permissible variation of 1/8” in 10’ from plane with no more than 1/16” variation in 24” when measured from the high points in the surface.)

Lippage can become a real problem when the lights are turned on.

Allow me to state this another way:

  • Using tile that meets the requirements of ANSI A137.1 for Nominal Size, Caliber Range, Warpage and Wedging
  • Installing that tile on a substrate that meets the ANSI A108 requirements for flatness
  • Following the ANSI A108.02 and/or the tile manufacturer’s requirements for maximum offset
  • Following the details of the appropriate method selected from the TCNA Handbook for Ceramic, Glass, and Stone Tile Installation
  • Selecting the correct mortar or adhesive for the type of tile being installed and application it is to be installed in
  • Mixing the mortar or adhesive per its manufacturer’s instructions
  • Selecting the correct trowel and using it correctly to achieve the bond coat coverage rates required for the system equals a successful, long-lasting installation that will please the owner and end user.

Note that ANSI A108.02 states “…specifier and owner must approve the mockup and lippage.” In my opinion, the expense of purchasing an adequate percentage of tile to install the required offsets can be very minimal when weighed against the potential for lippage and lighting-related failures that can occur when manufacturer instructions and tile industry standards are not followed.

Industry standards and manufacturer recommendations of 33% or less offset for tiles with one or more sides 15” or greater are required because of the manufacturing process for tile. When ceramic tile is heated and cooled in the kiln, warpage can occur. This is a normal result of the manufacturing process. Many tile factories are excellent at controlling warpage, but it cannot be completely removed. That is why there are limits for how much warpage a tile can have detailed in ANSI A137.1 for tiles that are manufactured to meet that standard. Whether or not a given tile meets the warpage limit of ANSI 137.1 can be found in the information printed on the carton or on the manufacturer’s technical data sheet, or by contacting the manufacturer.

The NTCA Reference Manual contains valuable information about wall lighting and lippage control devices.

You are absolutely correct in noting that lippage resulting from a layout or offset pattern or other factors can become a real problem when the lights are turned on. This is especially true for walls when the lighting grazes the face of the wall or when there is a sharp angle of incidence from natural light on a floor. I have listed references on the following page for more information on this topic.

You are also correct in noting that lippage tuning devices can help mitigate these issues. The job of these devices is NOT to take the place of any of the standard requirements I described above, but they can be a useful tool to help installers remove the last bit of human error (typically a maximum allowed 1/32”) and to hold the tiles in place while the bond coat cures. I have listed references below for more information about these devices.

I do not know why manufacturers or distributors might show tiles in an offset pattern that is different than what is required for a specific tile or by industry standards. It could be oversight or lack of knowledge by the person designing or creating the mockups.

You are correct that it very often falls to the tile installation contractor and installer to be the industry expert that understands everything I have described above. The installing contractor and the installer are the last line of quality control before the installation goes in. When or if there is a problem after installation, it is the installer and installation contractor that gets the call. The installation contractor needs to have an excellent working knowledge of the industry standards, methods and best practices to be able to adequately communicate the potential issues during the bidding process and BEFORE the installation takes place. To avoid issues, contractors and installers should empower themselves with this knowledge and know how to identify problems and to stop and identify a resolution before proceeding with the installation. Other trades and professionals such as general contractors, architects, specifiers and designers will respect a knowledgeable tile contractor that is able to clearly communicate what must be accomplished and why. Mockups are a key element of this process and are strongly recommended.

I described the key elements of the ANSI standards that pertain to this discussion of your questions. In addition, there are several other key areas you can use to inform yourself and communicate to other about this subject. They include:

  • 2018/2019 NTCA Reference Manual section on Critical Lighting Effects on Tile Installations on pages 125 – 132.
  • 2018/2019 NTCA Reference Manual section on Lippage Control Devices and Edge and Lippage Mechanical Tuning Devices on page 172.
  • 2018 TCNA Handbook section on Substrate Requirements.  See the section on Substrate Tolerances and Large Tile on page 31.
  • 2018 TCNA Handbook section on Lighting and Tile Installations on page 34.
  • 2018 TCNA Handbook section on Flatness and Lippage on page 36.
  • 2018 TCNA Handbook section on Grout Joint Size, Layouts, and Patterns on pages 37-38.
  • 2018 TCNA Handbook section on Finished Tilework on page 39 (especially the section on “Visual Inspection of Tilework”)

I encourage you to read and become familiar with all of the standards, methods and best practices I’ve described above in your NTCA Reference Manual, TCNA Handbook and ANSI standards. This will help you be even more confident in describing why installation standards and manufacturer instructions must be followed. Any deviation outside of following them often becomes risk accepted by the installation contractor because at the beginning, middle and end of every job, the tile contractor is the industry expert.

As you and I know, tile isn’t simple or easy. Sometimes, for very good reasons, we can’t always give the owner or specifier what they think they want. Contractors such as yourself that have access to the NTCA member benefits of technical support and education can better communicate the need to apply recognized industry standards, methods and best practices for successful installations. As you know, membership in the National Tile Contractors Association is a major source for help in understanding the standards and how to apply them and avoid issues BEFORE they happen.

We encourage designers, architects, GCs, and specifiers to attend our many workshops and other education programs, or to become an NTCA member themselves. Please feel free to direct them to our website and calendar of events at www.tile-assn.com and click on the Free Educational Workshops link under Education & Certification on the home page. You are doing a great job in asking the right questions. I hope this helps. 

Looking for documentation for flooded houses with tile floors


We are working with flooded storm victims from Hurricanes Harvey and Irma. The issue we are facing is that these homes were inundated with 3-8 feet of water for 2-7 days…category 3 water, which includes sewage and other toxins. The insurance companies and the National Flood Insurance Program refuse to consider this flooring damaged and are not paying for it.

Our research has shown us that, after a period of time after the storm, these tiles become loose due to water finding its way under the tile and causing damage to the adhesives. In addition, this also allows contamination to the flooring system. It was also noted that some ceramic tiles are porous, and the tiles themselves could be damaged or contaminated.

Based on the conditions above, we are looking for some documentation or recommendations stating the following about the tile floors in this situation (average age of tile install 5-10 years):

1. That the tile floor is recommended to be replaced due to the reduction or loss of adhesion, and/ or

2. That the tile flooring itself, including the adhesive, may be contaminated and should be replaced.

We find it hard to believe that an average-aged home with tile floors would be completely sealed and have no water intrusion into the tile flooring system. I would love to discuss this with your team after you have discussed this issue. Thank you very much and we appreciate anything you could do to help us and the recent flooding victims.


There are a number of standards and best practices that guide tile installations in America. Installation and material standards and specifications are found in American National Standards Institute (ANSI) A108; A118; A136; A137.1; A137.2; A137.3. Installation best practices, methods and guidance are found in the Tile Council of North America (TCNA) Handbook for Ceramic, Glass, and Stone Tile Installation. In addition, manufacturer instructions for the application and installation of their setting materials and related products used in tile installations must be followed for every

Installation standards, methods and materials will vary depending on the particulars of any given installation. Is it for example:

  • A floor, wall or ceiling.
  • A wet area such as a shower or a steam room.
  • A residential or commercial installation.
  • Is the supporting structure wood or concrete or steel.
  • Is the tile ceramic/porcelain; stone or glass.
  • And many other considerations.

Because there are applicable standards, methods, best practices, procedures, materials and numerous details that apply differently to each of these installation types, one generic analysis cannot possibly apply to each. Installations that have been flooded and constructed to the requirements of tile industry standards, methods and best practices can withstand significant amounts of moisture better than other products. In flooded situations, forensic investigations may need to be conducted to determine the next steps.

For this reason, NTCA strongly encourages you to contact a NTCA Recognized Consultant to review your cases. Find a recognized consultant by going to the NTCA website at www.tile-assn.com and searching for recognized consultants under “Find a Member.” As an association of tile contractors and professionals, NTCA itself does not provide these consulting services.

Mark Heinlein, NTCA Training Director

Fire and Sound Rating for Wall Assemblies


I am a design consultant, working on existing nearly 100-year-old structures. We need to be in compliance with current code for fire separations one- and two-hour.

Due to the historical aspects of some of the structures we cannot do much to the exterior but can enhance fire safety when doing alterations that affect the interior walls and floors.

Since the Space Shuttle uses ceramic tiles on the outside of the hull to preserve the lives of the crew from the inferno re-entry heat, why can’t ceramic tile be a part of the fire-rated floor and possibly ceiling assembly?

The intrinsic value added is we may be able to make the assembly thickness narrower, thus keeping the first floor and existing ceiling at the 7’-6” minimum clear building code height. Net results could be no fire sprinklers required, in certain situations, greater fire safety, lower cost for the upgrade and possible new avenues for upgrading older existing structures using something with thousands of years of historical reliability that goes through several thousand degrees of heat, to get produced.


I can direct you to the 2018 edition of the Tile Council of North America Handbook for Ceramic, Glass and Stone Tile Installation.

In the TCNA Handbook you will find method RW800-18 and associated descriptions and details for Fire and Sound Ratings for Wall Assemblies. This method begins on page 293 and includes a variety of details and information on materials and layers to design and construct fire rated tile assemblies.

Copies of the TCNA Handbook are available for purchase through the NTCA store at www.tile-assn.com. I hope this helps! 

Mark Heinlein, NTCA Training Director

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