Using wall tile on a floor in a wet area


I am building a new home and learning things I never knew. One is regarding what tile can be put on a shower floor. I want a shower as in the attached inspiration photo. Apparently, they used a tile that is now discontinued. The new version I like is approved for a shower floor.  However, it is expensive and has divots/irregularities. I was hoping for something smoother and in budget.

Most black subway tile is not annotated as for shower floors. However, my sales representative is telling me that it is perfectly fine to use a wall tile on a shower floor. She is recommending a specific glazed ceramic wall tile 3×12 (black glossy).  Is she correct?

Answer – Part 1

Any tile considered for use in any application should have the manufacturer’s approval for the intended use. I suggest asking your distributor/salesperson to obtain the technical datasheet for the tile you are interested in. The TDS should specifically include information if the tile is acceptable for use on a floor in a wet area (such as a shower floor). If the TDS does not include this information, you can call the manufacturer directly to request this information or select a tile that is specifically rated for use on a shower floor.

Additionally, the durability of the tile in this application may or may not be affected by the type of shower pan being specified for this installation and its ability to properly support a soft-bodied wall tile.

Another consideration is the pattern and drainage system. If a running bond pattern is used (with a conical pitched floor to a center drain) it would result in lippage and accompanying puddling.  A running bond pattern with a linear drain system could help minimize any puddling. 

As you have discovered, tile is a complex science and art.  One of the most critical installations to construct is a shower. To ensure that you get all of the correct technical information you need for your installation, I strongly encourage you to employ an NTCA member contractor and a CTEF Certified Tile Installer. These contractors and installers own, understand, and apply the tile industry’s recognized standards, methods, best practices, and follow manufacturer instructions in the installations they construct. NTCA Members and CTEF CTI certified installers have direct unlimited access to the NTCA/CTEF technical team for training and detailed industry standards-based support in every installation they construct.

Please review the Ceramic Tile Education Foundation’s homeowner’s guide to hiring a qualified installer:  https://www.ceramictilefoundation.org/homeowners-guide-to-hiring-qualified-tile-installer

To find an NTCA member contractor in your area: https://www.tile-assn.com/search/custom.asp?id=2759

To find a CTI installer in your area:  https://www.ceramictilefoundation.org/find-certified-tile-installers

Question – Part 2 – 50% offset/lippage and saving money to cut large tiles into small tiles

Thank you so much for your help in my questions regarding shower tiles.  If you don’t mind, one other issue has arisen and I’d like to know the correct answer. It appears to my untrained eye that most 12″x24″ tile is laid so that each abuts the 2 adjacent tiles by 50% each. However, the sales associate said some governing body (Tile Layer’s Association??) had rules against that because of “lippage”?  Are there rules on how tile should be laid? If so, where is the resource for that? I’d like to know as being the homeowner, I assume I’m ultimately responsible for catching mistakes in the construction of my new home.

Also, is it better to purchase (at high cost) precut 4″x12″ or is it acceptable to have those cut by installers from 12″x24″?  A sales associate said the former is the better option.

Answer – Part 2 – 50% offset/lippage and saving money to cut large tiles into small tiles

These are excellent questions that are answered by the tile industry’s written standards and best practices.

It sounds like you are selecting a tile for a builder’s installer or tile contractor to the installer. I suggest asking your builder if their installer or contractor owns and applies the methods and standards in the Tile Council of North America Handbook for Ceramic, Glass and Stone Installation (TCNA Handbook), and the American National Standard Specifications for the Installation of Ceramic Tile.  These are the documents that answer your questions.

The associate you are working with is giving you solid advice based on these standards. The retailer you are working with is a strong supporter of NTCA and their staff and associates, many of which have attended our training programs, are knowledgeable about these things.

To answer your first question about the 50% offset for the 12×24 tile:

ANSI A108.02 Section is where the answer is.  I will paraphrase what it says; When tiles with sides longer than 15” are being set with their long sides next to each other they shall be set in a pattern with an offset of 33% or less. If an offset more than 33% is desired (such as a 50% offset), the specifier and owner must approve a mock-up and agree to the lippage that may result from this type of pattern being installed.

The reason for this is that some tiles have what is called warpage as part of their manufacturing process. Warpage is when the tile is bowed in the middle. The ends of these tiles may be lower than in the middle of the tile.  When tiles longer than 15” are set next to each other in a 50% offset, this puts the high part of the middle of one tile directly opposite of the low part of the end of the adjacent tile. This can result in a difference in the height elevation of the plane between the two tiles.  This difference in the plane is known as lippage.  To quote the TCNA Handbook: “Lippage is a condition where one edge of a tile is higher than an adjacent tile, giving the finished surface an uneven appearance. Lippage is inherent in all ceramic installation methods and may also be unavoidable due to the tile tolerances, in accordance with ANSI A137.1”.

Not all tiles have warpage.  There are industry standards that describe acceptable warpage. Some tiles are made to meet those standards, some are not. The tile manufacturer can tell you if their tile meets the standard for warpage.  It is in ANSI A137.1.

Some manufacturers will have specific offset requirements for their tiles.  They may require a 20% or 25% maximum offset.

So, if you would like a 50% offset, you need to ask your tile contractor to lay them out or physically install a few so you can view them as they will look in the finished installation. At that time you would approve and accept (in writing) any lippage that occurs as a result of setting them at a 50% offset.  You will own and live with this installation – it is your decision to approve or reject the mockup.

To answer your second question about cutting 4×12 tiles out of 12×24 tiles:

The TCNA Handbook for Ceramic, Glass and Stone Tile Installation states:  Tiles should not be field-cut to size to accomplish modular patterns or to align grout joints, as field-cut edges will be dissimilar from factory edges and cannot be held to the same squareness tolerance.

This is not the desired practice.  In reality, it is not less expensive as your tile contractor should rightly be expected to charge labor and materials to cut down and smooth or hone the tiles. The tile contractor likely has excellent tools, but they may not be of the same grade as the tile factory and with human error, there may be variations from tile to tile after they are cut.  Expect the labor price will increase as more time is needed to ensure all tiles are well matched and finished.

Depending on the tile body and glaze, this practice may present an opportunity for chipped tiles. A large amount of additional tile may need to be purchased at the outset to account for this possibility.

For review:

As I mentioned in our last conversation, to ensure that you get all of the correct technical information you need for your installation, I strongly encourage you to employ an NTCA member contractor and a CTEF Certified Tile Installer. These contractors and installers own, understand, and apply the tile industry’s recognized standards, methods, best practices, and follow manufacturer instructions in the installations they construct.  NTCA Members and CTEF CTI certified installers have direct unlimited access to the NTCA/CTEF technical team for training and detailed industry standards-based support in every installation they construct.

Please refer to the links above.

I hope this information helps.

Emphasis on eliminating lippage grows along with tile formats

With the increased popularity of larger tile formats in recent years, the necessity for an efficient system to manage lippage issues has grown as well. Lippage is the condition where one tile edge is higher than an adjacent edge, resulting in a finished surface having an uneven appearance. This is a major concern for property owners, as it can be a safety or tripping hazard, as well as being unsightly.

Inherent bowing of tiles can add to the lippage problem, especially the wood-look plank offerings. And increased weight associated with larger tiles can cause tiles to slump.

An effective tile leveling system should be strong enough to align and support large-format and heavy tile surfaces, and have the ability to apply enough force to effectively eliminate bowing while securing tiles in place as the mortar bed dries.

Steve Sprung

With the advancements in porcelain and compact-surface manufacturing available today, the industry is seeing an enormous increase in the popularity of “thin” tile or gauged porcelain tile panels (GPTP), noted Steve Sprung, Product and Marketing Manager, RTC Products. Installing these panels or slabs not only requires extensive knowledge, but also a certain amount of training and/or certification. The common skill set for standard tile installation may apply, however current tooling will not suffice. 

“This introduces our craftsmen to an entirely new segment of tools and installation products,” he explained, “as well as a new standard specification, which can be found within ANSI A108.19 Interior Installation of Gauged Porcelain Tiles and Gauged Porcelain Tile Panels/Slabs by the Thin-Bed Method bonded with Modified Dry-Set Cement Mortar of Improved Modified Dry-Set Cement Mortar. With this written standard, installers now have access to information on methods and best practices to install a material – that until recently – had many unknown factors.”

Lippage Control Systems

1 Miracle Sealants/Rust-Oleum

Preventing lippage is designed to be fast and easy with Levolution. This all-in-one system promises perfectly spaced and level tiles. With 1/8”, 1/16”, and 3/16” spacer size options, it fits all standard or large-format tile up to 1/2” thick – including warped or flexible tiles. rustoleum.com

2 Progress Profiles

The company’s Proleveling System is a patented laying system that is designed to allow quick and easy work. It is composed of only two practical and easy-to-use elements. A leveling base allows it to separate and join ceramic, marble, natural stone or thin tiles. The transparent polyethylene pommel cap, inserted in the centrally threaded stem of the leveling base, allows regulation of pressure on the surface and to align tiles’ grout lines with precision. progressprofiles.com

3 RUBI Tools

The Delta Tile Leveling System prevents lippage on floor and walls, stopping the tiles from moving while the adhesive sets and reducing the number of corrections to the position of the tile itself. The system of wedges and flanges, designed for formats of 30 x 30 cm or greater, presses down on the highest piece until it is evenly positioned with the adjacent tiles. The system’s pliers are designed to be used in floor and wall tile installation applications to apply the necessary pressure to the wedge to allow the leveling of the tile. Once the installation is complete, the elements are removed by impact (kick or mace), striking the flanges in the direction of the joint. rubi.com

4 Russo Trading Company (RTC)

The company’s Spin Doctor is designed to be a quick and convenient solution to reduce tile lippage. The 1/32” Spin Doctor Kit has been developed for the installation of gauged porcelain tile panels (GPTP) and complies with the ANSI A108.19 standard for installation in accordance with spacing and lippage tuning systems. The Spin Doctor 1/32” Pro Kit includes 200 Caps, 500 Posts, 200 Clear View Shields (shields must be used when installing GPTP), and is available in 1/16”, 1/8” and 3/16” post sizes. rtcproducts.com

Caulking corners and Lippage issues


My biggest question is regarding plane intersections, specifically a corner where two vertical walls meet inside a shower. I know that we should be caulking – not grouting – the corner joint, but what’s the best way to go about doing this? Should we put in the backer rod prior to grouting and then remove the backer rod (if the joint is small enough to not need it) before applying the silicone? Otherwise, it seems to me that it is going to be tough to keep that joint clean of grout, and once the grout is in there it essentially locks out the ability for expansion, right? Or am I thinking about this wrong?

Also I’m hung up on lippage (no pun intended!), especially when using bigger (say 12˝ x 36˝ or 12˝ x 48˝) tiles. Even when not having any overlap in the pattern so as to minimize the potential for misaligned height differences between the centers and ends of the tiles, it seems to be very, very difficult to get a truly flat install even when using a lot of leveling spacers. I know that the lippage requirements increase based on the tile size, but what else can we do besides trying to keep the pattern helpful to minimizing lippage and spot-checking tiles and not using any badly warped tiles? Seems like a lot of waste that way too.


Your description in your first question is correct. ANSI A108 recommends grouting before installing sealant. Grout hardening in the change-in-plane joint is problematic. Installing the backer rod before grouting, then removing and replacing it is a good way to keep the joint clean. Use ASTM C920-rated silicone grout-color coordinating sealant for the joint. ASTM C920 sealant requires use of a backer rod for best performance.

For your second question – to begin with, as discussed in our workshops, substrate flatness for large-format tile is critical. Lippage tolerances do NOT increase with tile size. Layout, pattern and grout joint width are all components of minimizing lippage and keeping it within tolerances. All of these are standardized measures required by ANSI A108. Often, it is of crucial importance to use tile manufactured in accordance with ANSI A137.1 to achieve less-than-maximum allowable lippage in an installation. 

Mark Heinlein, NTCA Training Director, NTCA Technical Trainer