Large-format tile has been around for a while now, but how is it defined? There is no true definition for large-format tile, with the exception of the category of glass tiles. The American National Standard Specification for Glass Tile, ANSI A137.2.3, defines a large-format glass tile, but ANSI A137.1 does not do so for ceramic tiles.
What is defined is the substrate flatness tolerance in ANSI A108.02 for tiles over 15″ on one side, which are generally accepted as large format. This standard states that the substrate should have no variation greater than 1/8″ in 10′. This level of flatness is required due to the increased length of the tile, and is doubly important when these tiles are installed in an offset pattern. It should be noted that the standard also states that the substrate cannot be more than 1/16″ in 24″ out of plane. This is a much tighter tolerance than the customary 1/4″ in 10′ variation that many are used to.
Grout joint width: bigger is better
Another important consideration before installing these large tiles is the width of grout joints within the installation. With the introduction of larger tiles, designers and end-users expect that the grout joints should narrow so that there is less grout maintenance, and a more monolithic look.
But, ANSI A137.1 “Table 8: Pressed Floor Tile” and “Table 10: Porcelain Tile” states the maximum caliber range for tiles over 6″ is 2.0mm or 5/64″. This means that these larger tiles can vary in size more than 1/16″. According to this standard, the grout joint width is allowed to be three times the facial dimension variance of the tile. A wider grout joint with larger tiles is needed to keep the grout joint width and tile layout as symmetrical and square as possible, while at the same time reducing the chance for excessive lippage.
Every tile contractor reading this has multiple stories of the end user wanting 1/16″ or less grout joints with larger tiles, saying “it looks better” or “I don’t like dirty grout joints.” I can attest that on multiple inspections I have made, the tile installer got in trouble when they were trying to please the customer instead of following industry standards or, more importantly, tile manufacturer’s recommendations for minimum grout joint width.
Mortar coverage on larger tiles
Mortar coverage on larger tiles is also extremely important. ANSI A137.1 “Table 8: Pressed Floor Tile” says the maximum edge warpage for tiles over 6″ is 2.0mm or 5/64″. Rectified ceramic tiles are a maximum of 1.3mm. In “Table 10: Porcelain Tile,” the maximum edge-warpage is 1.8mm, 1.3mm for rectified tile 24″ or less, and 1.8mm for rectified tiles over 24″.
For this reason, flat-back troweling a thin layer of mortar on the back of the tile, though not required, may help make up a little of the tile warpage. More importantly, that step will help create better bonding to the properly-troweled tile mortar on the substrate. A minimum of 80% mortar coverage on the tile is required in most applications. Careful attention to fully supporting the edges and corners of the tile with mortar will help to stop edge crushing and corner breaks. 95% mortar coverage on the tile is required in wet areas and exterior applications. It is vitally important to inhibit moisture intrusion into these tile installation systems, especially in exterior freeze/thaw climates.
Large-format tiles are getting even larger, so it has now become imperative to follow the tile manufacturer’s recommendations, ANSI A108 standards, and to know the ANSI A137.1 manufacturing standards. These tools are critical to proper, long-lasting and superior-performing tile installations.
James Woelfel
James Woelfel is the President of Artcraft Granite Marble and Tile in Mesa, Arizona. As a third-generation family business, Artcraft Granite, Marble & Tile Company is an NTCA Five-Star Contractor Member and his company has proudly worked with integrity for more than 85 years in providing quality craftsmanship in tile and stone installation. Woelfel is also Chairman of the NTCA Technical Committee since 2007 and is a voting member of the TCNA Handbook and ANSI A108, 118, and 137.1 Committees. He served as president of the NTCA from 2015-2017, was the 2011 recipient of the NTCA Tile Person of the Year Award and the 2019 recipient of the NTCA Ring of Honor. Woelfel is also an NTCA Recognized Consultant and a highly-rated speaker at industry shows such as Coverings, The International Surface Event (TISE), and Total Solutions Plus.
Nyle Wadford
Nyle Wadford is President of Five-Star Contractor Neuse Tile Service in Youngsville, NC. For more than 60 years, the Wadford family has been providing quality tile and stone installations to residential and commercial customers in the Raleigh area. Wadford has also been Vice Chairman of the NTCA Technical Committee since 2008 and a voting member of the TCNA Handbook and ANSI ASC A108 Committees since 2010. He received the NTCA Ring of Honor in 2021, was the NTCA Tile Person of the Year in 2012, and served as the association's president from 2010 to 2012. He is an NTCA Recognized Consultant, a frequent speaker at industry trade shows, and continues to serve the association in various volunteer roles.
