TECH TIP TUESDAY: Q & A WITH NTCA TRAINING DIRECTOR MARK HEINLEIN

Question:

Do you have any guidelines on how to install porcelain tile according to ANSI Guidelines you could send me, please?

Mark’s Reply:

Thank you for contacting the National Tile Contractors Association.

Below, I have listed for you the primary tile industry standards, methods and guidelines for the installation of porcelain tile.

  • American National Standards Institute (ANSI) A108 and A118 – American National Specification for the Installation of Ceramic Tile – Material and Installation Standards
  • ANSI A137.1 – American National Standard Specifications for Ceramic Tile
  • Tile Council of North America (TCNA) Handbook for Ceramic, Glass, and Stone Tile Installation

These standards and guidelines are extensive in that they cover many types of installations using tried and true best practices, methods, techniques and materials recommended for a variety of structures and substructures.  I am not able to send these to you, but they are available for purchase at this link: https://tile-assn.site-ym.com/store/ListProducts.aspx?catid=398904

If you are a tile contractor, these standards will be your guide for all of your tile installations.  I encourage you to purchase them and become familiar with them and use them in your installations.  In addition, I encourage you to explore membership in the National Tile Contractors Association.  More information can be found here:  https://tile-assn.site-ym.com

If you are an owner considering accomplishing a tile installation, I strongly encourage you to interview and hire a qualified, certified contractor and installer who owns, understands and uses the tile industry standards I listed above.  Please research the below links to locate an NTCA Member contractor and CTEF Certified Tile Installer near you.

Why Hire an NTCA Contractor: https://tile-assn.site-ym.com/?page=whyhire

Locate an NTCA Contractor: http://tile-assn.site-ym.com/search/custom.asp?id=2759

Why Hire a CTEF Certified Tile Installer: https://www.ceramictilefoundation.org

Locate a CTEF Certified Tile Installer:  https://www.ceramictilefoundation.org/find-certified-tile-installers

I hope this helps.

Mark Heinlein,

NTCA Training Director

Tech Tip Tuesday: Q & A With NTCA Training Director Mark Heinlein

Member Question:

I need installation guidance to install a ceramic or porcelain tile over a concrete slab/sidewalk. This will be outside of a church and it is currently a concrete floor and curb. What would you recommend we use at the edge and expansion joints?

Mark’s Response:

There is a lot to consider before tiling a project like this one.  Since you may not have yet received your 2017 TCNA Handbook, I have attached a couple of photos of two methods (F101 and F102) that may be most applicable to your installation.

F101 describes an on ground concrete substrate with proper drainage below the slab, bonded mortar bed, ceramic tile and optional waterproofing / crack isolation membrane.

F102 describes an on ground concrete substrate with proper drainage below the slab, cementitious bond coat and optional waterproofing / crack isolation membrane.

Both of these methods will require proper drainage beneath the slab and drainage for surface water runoff from the finished surface and further drainage into the landscaping.  If the slab abuts a permanent structure, you will want to be certain that the drainage is slope away from the structure – the general rule would be 1/4” vertical slope per 12” of horizontal run.  Besides methods F101 and F102, there may be other methods and materials that will help with system drainage if that is an issue.

Prior to proceeding you will need to determine if this is a well cured slab and whether it is dimensionally stable and free of cracks, films, curing compounds, sealers, etc. and whether it’s surface has been at least steel troweled with a fine broom finish suitable for mortar to bond to it.  The flatness requirements of 1/4” per 10’ must be met for application of an F101 Thick Mortar Bed or for F102 direct bonding of tiles less than 15” on one side.  For direct bonding of tiles with one side 15” or longer the slab must meet the 1/8” per 10’ flatness requirement before the tile (or membrane) is to be set.

You will see that both of these methods list a membrane as optional.  Inclusion of a membrane will help with waterproofing above the substrate and a degree of crack isolation from minor existing or future in-plane cracks.  If the slab is abutted to a structure, I suggest looking for a way to flash the membrane up the side of the structure, potentially beneath the siding (if any).  The “Membrane Options” section of the method lists the specific membrane requirements and also points to Handbook methods F125-Partial / F125 – Full for crack isolation.

Some membrane manufacturers state that their membranes will be able to span certain types of joints if installed per their instructions and as part of a full system warranty (use of one manufacturer’s mortar, grout, membrane, sealant, etc.).  Installation of a membrane will help with waterproofing, some system drainage, and to protect against efflorescence from the substrate.

The “Materials” section defines the specifications for the tile and setting materials to be used in this method.

You are correct that this installation will need Movement Accommodation Joints.  TCNA Handbook Method EJ-171 provides the details.  As a minimum, those joints should be placed around the perimeter and at every change in plane or where the tile meets a different material.  Expansion joints in the concrete slab must be honored upward through the finished surface of the tile.  Expansion, Isolation, Construction, Contraction and other joints must be addressed.  For an exterior installation, joints throughout the tile field are required every 8’ – 12’ depending on materials and environmental conditions.  Appropriate joint width must also be determined based on environmental conditions the installation is expected to be subject to.  Sealants complying with ASTM C920 with an appropriate designation for this type of installation will be required for the soft joints.  As this is a traffic area, a sealant with a shore A hardness rating of 25 or greater should be considered.  Conversely, a manufactured joint may be available to use.  As we discussed in our workshop, it is the responsibility of the design professional or engineer to determine the location / placement / width / construction of these joints.  Method EJ-171 provides details on constituting these joints – but is too much information for me to forward in this e-mail.

Since this is an exterior installation with some potential of freeze/thaw cycling, expect there to be some system / component degradation over time that may require routine maintenance.

You will want to finish and protect the exposed edges of the tile with a commercially rated, durable metal trim such as brass or stainless steel. Bullnose, or tiles that have been custom bullnosed for the project may also work well depending on the expected use and conditions.

I hope this helps point you in the right direction.  You should have your new 2017 TCNA Handbook soon so you can refer to these methods and all of the other great guidance it contains.

Mark Heinlein

NTCA Training Director

TECH TIP TUESDAY: Q & A WITH NTCA TRAINING DIRECTOR MARK HEINLEIN

Consumer Question:

The concern that I have at this time is the installation of soft joints at the change of plane in the corners of the tub surround. The product is a 12″ x 24″ marble.

 

 

 

 

 

 

 

 

 

 

 

The tile pieces most definitely butt up against one another and it is my belief that the tile installer is going to place a bead of caulk up along the exposed surface of the two.
I am concerned this is not a soft joint to allow for movement of the tiles, but rather a bead of caulk to hide the connection (more aesthetic than functional).  Would this be a concern for you? If so, what types of issues may I have in the future if there is no soft joint?

 

Mark’s Reply:

Thank you for contacting the National Tile Contractors Association!

The Tile Council of North America Handbook and ANSI Standards require functioning open movement joints at changes in plane.  If those joints are tight butted there will be no room for them to properly function to absorb the natural flexing, movement, expansion and contraction that is inherent in all construction.  Without being there in person I am not able to comment definitively however, the joints in your photos do appear to be either tight-butted or have too tight of a joint.

Movement joints at changes in plane are required and are functional and should be filled with a flexible sealant appropriate for the area it is being used.  For a wet environment such as a shower, an ASTM C920 sealant such as a 100% silicone or urethane can be used. These sealants are manufactured to match as closely as possible the grout color.

Before applying the sealant in your marble installation, a test sample should be done along the edge of a scrap piece of marble.  Some colors of sealants have colorants that may absorb into the soft stone and may cause staining that can be visible along the edge of the tile. This is a common pre-installation test that should be done with all marble installations.  A phone call to the technical department of the sealant manufacturer may help determine which of their colors are best suited for soft stone.

The best way to find an NTCA Recognized Consultant in your area is to review our list at this link:  http://www.tile-assn.com/?page=recconsultants. These are highly regarded consultants that may travel regionally or nationally.  Feel free to let them know about the conversations we have been having.

I hope this helps.


Mark Heinlein, NTCA Training Director

TECH TIP TUESDAY: Q & A WITH NTCA TRAINING DIRECTOR MARK HEINLEIN

Contractor Question:

Mark,
I am thinking about putting a heating TapeMat in the floor of my bathroom.  The manufacturer’s literature suggests a modified thin-set mortar.  I am using a large format tile (12” x 24”).  I am placing the tile on a 3/4 inch plywood subfloor with a 1/4 inch Hardy board backer.  The floor is supported by 2”x12” floor joists spaced at 16” on center.  The bathroom is L shaped and is  8’x4’ with a 3’ L.  The 8’ wall is an exterior wall. Would an unmodified mortar work as well? Is it even advisable to use a modified mortar with a large format tile?

Mark’s Reply:

Thanks for the info.

Assuming ceramic/porcelain tile is being installed, the industry recognized method found in TCNA Handbook is RH135-16.  The method describes the details for an electric radiant heat system encapsulated in mortar over backer board on a plywood subfloor with joists 16” on center, which is the installation you have described.

It sounds like you are not installing a waterproofing membrane in the system.  In that case, the required thinset mortar for the cementitious bond coat is an ANSI A118.15.  In other words, an Improved Modified Dry-Set Cement Mortar is required.

The mortar you select should have the words “Meets ANSI A118.15” stamped on the package.  Be certain to carefully follow the mortar manufacturer’s instructions for the proper amount of water, mixing instructions, slaking time, open time, etc.

You asked whether it is advisable to use a modified mortar with a large format tile.  It is.  In fact, many manufacturers are now producing highly modified mortars specifically designed for Large and Heavy Tile.  You may find mortars labeled as “LHT” for this reason.  These mortars have specific properties to support the installation of large and heavy tiles on floors and walls.  Some allow for a thicker bond coat.  This is the type of mortar I would look for when installing an electrical heating tape mat system in the bond coat layer.

If you are using a membrane in the system, it may be advisable to use a less highly modified mortar (such as an A118.4) or even an unmodified thinset mortar (A118.1).  Check with the manufacturer of the membrane for their specific mortar recommendation.

Please make certain the surface of your plywood subfloor is flat to meet the industry standard tolerance of 1/8” in 10’ as required by ANSI A108 before you install the backer board.  This will ensure you have a flat finished tile surface on your large format tile installation.  Use a rapid setting patch material to fill low spots and a belt sander on the high spots of the plywood.  Do not use more or less thinset to help you flatten your installation while you set tile.  Doing so will prove problematic for you and your installation.

Membership in the National Tile Contractors Association is a valuable resource for any professional tile contractor or any contractor who installs tile.  NTCA is committed to improving installations and performance of contractors throughout the tile industry.  Our primary mission is training based on the tile industry standards I have described above.  Every installer should own and be familiar with the standards, methods and details that guide the tile industry.  I would be happy to discuss with you and your tile installation contractors the many benefits of membership in NTCA.  Please feel free to contact me, or Jim Olson at jim@tile-assn.com for more information.  Also please visit our website at www.tile-assn.com.

The Ceramic Tile Education Foundation (CTEF) supports education and training in the tile industry.  The Certified Tile Installer (CTI) program is a highly sought after certification for tile installers who wish to achieve a higher level of professionalism and recognition in the tile industry.  Please visit the CTEF website at https://www.ceramictilefoundation.org to locate a Certified Tile Installer or contact Kevin Insalato at kevininsalato@gmail.com for more information on how a contractor can become a CTI.

I hope this helps.

Mark Heinlein, NTCA Training Director

 

Tech Tip Tuesday: Q & A With NTCA Training Director Mark Heinlein

Consumer Question:

Hi! Recently, our new tile floor began cracking. Our builder took up the damaged areas, fixed deflection, and replaced damaged tiles. Now, more tiles in other areas are cracking. Is it standard practice to continue piecing the floor together or is it better to rip out the whole floor?

Answer:

Thank you for contacting the National Tile Contractors Association.

It is not at all standard to have to make repairs like this to a new tile installation.

What is standard is to ensure the structure including the subfloor and substrates that will support the tile installation are properly engineered, designed and constructed before the tile installation begins. There are standard requirements to meet tolerances for deflection.  When deflection and substructure requirements are met, tile installations can be designed and installed using additional tile industry standards, methods, best practices and techniques.

The primary tile industry standards are found in these publications:
American National Standards Institute Specifications for the Installation of Ceramic Tile (ANSI A108)
American National Standards Institute Material Specifications (ANSI A118)
Tile Council of North America (TCNA) Handbook
In addition to deflection, there may be other factors that could be leading to this failure in your tile system.  Tile installations are complex.  Every aspect of the installation must be performed according to industry standards and material manufacturer instructions to ensure a long lasting successful installation.

Ask your tile installer which standards and methods from the above listed publications they followed to install your project.

Is your tile contractor a Ceramic Tile Education Foundation Certified Tile Installer (CTI)?  CTIs are recognized by the tile industry to have the necessary knowledge of these industry standards along with the proven skills and experience to construct long lasting tile installations.  You can search the list of CTIs in your area at this link:  https://www.ceramictilefoundation.org/find-certified-tile-installers

Is your installer an NTCA member or an NTCA 5 Star Contractor?  NTCA member contractors can be located here:http://www.tile-assn.com/search/custom.asp?id=2759  Membership in the NTCA is a valuable resource for any professional tile contractor or any contractor who installs tile.  NTCA is committed to improving installations and performance of contractors throughout the tile industry.  Our primary mission is training based on the tile industry standards I described above.

NTCA 5 Star Contractors that employe CTIs can be located at this link:  http://www.tile-assn.com/search/custom.asp?id=2838

Every installer should own and be familiar with the standards, methods and details that guide the tile industry.  If your contractor is not familiar with the standards or if they are not an NTCA member or Certified Tile Installer, I would be happy to discuss with them the importance of these programs.  Please feel free to have them contact me, or Jim Olson at jim@tile-assn.com for more information.

The NTCA and the entire American tile industry want you to have a beautiful and functional and safe installation that will stand the test of time and that will make you happy and comfortable and proud to own. Employing Certified Tile Installers and NTCA member contractors is a step in the right direction to ensure a successful tile installation based on tile industry standards.

I hope this helps.

Mark

Ask the Experts – August 2017

QUESTION

An architect has requested my input relative to developing a labor and material specification for installing new porcelain floor tile over existing granite floor tiles in a high-traffic lobby in a commercial office building. Can you direct me to any relevant literature or information that addresses such applications? Thanks.

ANSWER

I suggest referring your architect to the 2016 TCNA Handbook methods TR611, TR711 and particularly TR712. Please note that if the installation is not, or cannot be made acceptable for tiling over with a thin bed system, Method F111, or another method, may be required.

As described in TR712, it is critical that the existing installation be sound, well bonded and without structural cracks. It must be determined if the existing installation will properly support the new installation. The existing tile and its bond to the substrate and the condition of the substrate will all reflect on the performance of the new installation. If there are existing structural cracks, their cause will have to be explored before using the existing surface as a substrate. It is advisable to consider the need for a partial or full crack isolation membrane. Those methods are F125-Partial and F125-Full in the TCNA Handbook.

Any existing expansion in the substrate beneath the existing installation must be honored in the new installation. TCNA Handbook Method EJ171 will be the reference to all expansion and other types of joints that must be honored and designed and installed into the new system. Note that EJ171 states the architect shall specify the location of any expansion joints and other soft joints throughout the field and other locations such as the perimeter and any change in plane. Have the architect specify in writing (via drawings) where these are to go and which materials and EJ171 details should be used to construct them.

Checking for the ability to bond to the existing tile is imperative. If there are sealers or oils or waxes, etc., on the existing sur- face, they must be removed. If the tile is highly polished, it will likely require mechanical abrasion to allow the bond coat to adhere. I suggest doing a simple bond test by mixing and placing (including keying in) the mortar that will be used for the project onto the surface of the existing tile. Do this in several representative locations. Allow the mortar to cure for several days then remove it to determine how well it was able to bond to the substrate. You can select the trowel you will use for the job, comb the mortar and place a tile on top of the bond coat as a means of checking your coverage and inspecting the overall performance of the bond coat at the same time. Document everything about this test in writing and with photographs. Repeat the test with other materials and

tools if needed.
Depending on the results of the

bond test, it may be advisable to apply a primer that will facilitate bonding. Some setting-material manufacturers have specific primers designed for this purpose. They can recommend their best products (including mortar) for this application. I suggest using a system approach from one manufacturer that includes any primers, membranes, mortars, grouts, sealants, sealers, etc. I advise you to contact the technical representative of your preferred manufacturer about this job. They will be happy to assist you in writing a system warranty specific to this job.

Please also refer to ANSI A108.01 2.6.2.2 as an important reference for this installation.

It is necessary to ensure the substrate meets industry standard flatness requirements found in the ANSI Standards and TCNA Handbook. Please refer specifically to ANSI A108.01 2.6.2.2.

Generally speaking the standard is:

  • 1/4” in 10’ for tile with any side 
less than 15”
  • 1/8” in 10’ for tile with any side 
15’ or longer
  • Flatness can be checked with a 
10’ straight edge.

Financial allowances must be included in the specification, and proposal for labor and materials to flatten and otherwise prepare the substrate must be included in the specification and proposal. 
Tiling over sound existing tile as a substrate is an excellent way to proceed. As with any tile installation, careful research, proper planning, using the recommendations of industry standards, following manufacturer instructions, using a system approach, good communication and documentation before you proceed will mean a great and long-lasting installation and will make all parties happy with the end result. You are already on the right path. I hope this helps!

Mark Heinlein, NTCA Trainer/Presenter

Ask The Experts: July 2017

QUESTION:

I have a client with glass tiles cracking on an install. The GC admitted to not installing with a crack suppression membrane. They also drilled pilot holes for a door install that resulted in cracking. The tiles associated with the holes were installed before drilling. The final comment by the client was the cracking was from the back, and did not come through the face.

In your opinion, is it likely the lack of a crack isolation membrane created the opportunity for all of these tile cracks?

 

ANSWER: 

It appears to me that the crack at the window wall may be related to structural stresses within the framing or deflection in the substrate. The crack at the control valve may be related to structural stresses such as deflection within the substrate that was not well supported at the valve location. The cracks from the drill holes are likely related to the physical and heat stresses placed on the tile during the drilling process and may also be related to deflection in the substrate if the substrate was not well supported in this area. A crack isolation membrane would likely not have prevented the cracking.

There are other potential issues that can cause large-format glass tile to crack. They would include: Incorrect mortar or adhesive selection; mortar cure time (which will vary based on the mortar used and whether a waterproof membrane was used); thermal expansion from light or hot water; lack of expansion joints; deflection in the substrate; etc.
– Mark Heinlein,
NTCA technical trainer/presenter

QUESTION:

I’m dealing with customers who are unhappy about their recent tile installation. They feel the tile has too high a color variation. Could the installer have laid out the tile incorrectly? Whose responsibility is this – the installer’s, or mine? Thanks for your help.

ANSWER:

Per our conversation, on page 2 of the 2016 TCNA Handbook there is a section that deals with aesthetic classification. It specifically talks about variations in color, texture and appearance, and how tile suit- able for TCNA Handbook installations must meet specifications out- lined in ANSI 137.1. This ANSI standard sets performance and aesthetic criteria for many types of tile. Using tile that meets ANSI 137.1 ensures a degree of quality and consistency among tiles.

This chart from CTDA illustrates the ranking of shade variation levels, from the most uniformly shaded V1 to V4, which represents a tile with the highest degree of shade or color variation. A V0 tile is very uniform in appearance and smooth in color, with a color difference of less than 3 Judds when measured by a colorimetric spectrophotometer.

Tiles can have a V (variation) designation from V0 to V4. V0 tiles are very uniform in color and shade. V2, V3, V4 tile all increase in their randomness of color with V4 being the most random. Is the tile in question an ANSI 137.1 tile and what is its V designation?

The TCNA Handbook says that tile should be installed from several boxes in a random fashion to avoid aesthetic issues. Are you aware if the installer did this? How much was installed before the variations were noticed? How quickly did the installer report this to you?

It is common practice in our industry to report any defects or issues with the tile prior to installation. Many tile manufacturers even have disclaimers on their boxes explaining that claims against the tile must be made prior to installation. Let me know the answers to these questions and I will try to help you further.

– Robb Roderick,
NTCA technical trainer/presenter

 

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Ask the Experts – June 2017

QUESTION

I was on a walk-thru today and attached are photos of a chip on an installed tile wall at the World Trade Ctr.  There are numerous chips like this on the job from damage by other trades after we finished installing.

The architect is calling out these tiny chips on the punchlists and I’m arguing about with him considering the tiny size.

Sure we can remove and replace chipped tile, but I think there would be more of a mess than they might want to deal with.

Is there any criteria for this?  Like if a chip is less than  1/16” it stays?

Please let me know, and thanks in advance.

 

ANSWER

There are no criteria that I am aware of that states what size chip is acceptable.  It is extremely unfortunate when other trades do not respect our installations.  There is some debate as to whether it is a tile contractor’s responsibility to protect our work, or whether it falls to the trade that comes behind us to use a modicum of precaution and protection.  Perhaps you will be able to bill the contractor that damaged your work for your time to repair the damage they caused.

Please refer to these standards:

  • ANSI A108 is the Tile Industry Standard Specification for the Installation of Ceramic Tile.
  • ANSI A108.02 is the General Requirements for Materials, Environmental and Workmanship.
  • ANSI A108.02 4.3 is the section that discusses Workmanship, Cutting, Fitting and Grout Joint Size.
  • ANSI A108.02 4.3.3 states “Smooth cut edges. Install tile without jagged or flaked edges.”

Other tile industry standards include:

  • TCNA Handbook (2016 Edition)
  • ANSI A108 / A118 / A136 (Installation and Material Standards)
  • ANSI A137.1 (Ceramic Tile)

In addition, you will want to have:

  • ANSI A137.2 (Glass Tile)
  • A137.3 (Gauged Porcelain Tile / Panels – standard just approved at Coverings in April)

I hope to see you later this year when I am in the area.  – Mark Heinlein, NTCA technical trainer

QUESTION

I have a customer who wants wanted to use pebbles on the floor of the shower with grout joints washed really low. Are there standards or guidelines that relate to this type of installation that you can share with me?

ANSWER

The NTCA always encourages our members to use the standards and methods found in the TCNA Handbook for Ceramic, Glass and Stone Tile Installation, and the guidelines in The American National Standards Institute (ANSI).

In response to your question about the depth of grout in a grout joint: refer to ANSI 108.10 Installation of Grout in Tile Work.

In section 5.3.3 it states to “force a maximum amount of grout in the joint.” In section 5.3.4 it says, “All joints are to be uniformly finished.”

Part of the service we offer to members is technical support. We have in the past seen many instances where uncut pebbled stones have inhibited the flow of water in showers even with properly sloped assemblies, which in turn leave small puddles behind the stone affecting the uniformity of grout color. Also these small puddled areas — when not properly and regularly cleaned — can encourage mold growth when organic materials from soaps and shampoos are added to them. This is a significant enough problem that I’ve heard the 1/4 “per foot slope minimum requirements for shower floors may be changed to 1/2 “per foot slope to alleviate some of these issues. Not filling the joints full as directed by the ANSI standards previously cited could increase theses issues. – Robb Roderick, NTCA technical trainer

Low grout joints in a pebble shower floor go against standards and guidelines and can lead to problems. (Photo of correctly grouted pebbled floor courtesy of Stoneman Construction LLC).

Ask the Experts – May 2017

Several questions have been directed lately to our technical team concerning installing tile in elevators. Here are several responses:

QUESTION

I’m interested in installing tile on an elevator floor. Are there industry guidelines or standards for doing so? I have 3/4” of available depth to work with between the bottom of the elevator door and the floor.

ANSWER

There is no method for installation of tile on an elevator floor in our industry guidelines.

The elevator cabs chosen for some construction projects are not designed for tile or stone floor finishes. The manufacturer of these elevator cabs will list acceptable floor finishes, which usually only include soft goods such as vinyl, carpet, and wood products.

In order to be considered for tile or stone, the substructure should be constructed in such a way as to not to deflect or “bend” more than a small amount under a concentrated heavy load. There are elevator cabs that are designed to meet these minimum requirements but they are usually much more expensive so they are not chosen in most construction budgets.

As for installing tile in the most common elevator cabs that are not designed for it, it is risky and not recommended.

There are products available that may reduce the risk of cracking tile and grout joints such as epoxies, but the warranties come strictly from the manufacturers.  – Robb Roderick, NTCA technical trainer/presenter 

We are not aware of any documents or standards but can offer you some cautionary advice. 

The majority of elevator floors are designed to carry a specific number of passengers or maximum weight load.  This design criterion focuses solely on how many people the car will carry rather than the stiffness or rigidity of the steel floor.  A flexing floor is not a good environment for a tile installation.  The fact that the architect is specifying a plywood underlayment may help, but unless the architect is willing to guarantee that this floor structure design will meet a MINIMUM of l/360, the risk for success will rest with you.

Some contractors have had success in getting approval from manufacturers to use their epoxies to install tile in elevators. Make sure you get their warranty and recommendation in writing.

You mentioned you had 3/4” of available depth.  When completed, the elevator floor must meet ADA guidelines.  This means that the finished floor must be flush with the adjacent sill or not exceed the maximum rise allowed within ADA regulations.  Most times the addition of the plywood would exceed  that allowance and be non-compliant.– NTCA technical trainers Mark Heinlein and Robb Roderick, with CTEF’s Scott Carothers

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