By Dave Gobis
Experience is showing that large tile is much less tolerant of substandard floor preparation, poor installation practices and the use of basic thinset bonding materials as well.
Big tile is in and here to stay.
As technology grows, ceramic tile products continue to get bigger and thinner. End users love it; bigger tile means bigger fashion, less grout and easier maintenance. The promised benefit for the installer is faster installation and more money. But, anyone who has ever installed large tile can tell you it certainly isn’t easier or less time consuming to install. The bigger the tile gets, the more challenging the installation becomes. Having spent the last 13 years of my nearly 40 years in the tile industry providing technical assistance, I would have to say the most common call is no longer grout joint issues but lippage complaints. With bigger tile the technical challenges for good tile installations increase in complexity.
Substrate preparation for large tile is consistently deficient in several areas. The need for a properly prepared bondable surface gains greater importance with large tile. Fewer grout joints means much more strain occurs at the thinset bonding interface of both the tile and substrate. Shiny slabs have proven much more problematic with an 18-inch tile than with an 8- inch tile. All tile experiences some movement, and an installation with 50% less grout joints will move with much greater force.
While end users want the look of large tile, building contractors have not provided the flatter floors that such tile requires. That adjustment increases cost. In a perfect world, we would know ahead of time that we would be installing large tile and the more exacting tolerances required of substrates could be specified prior to construction. To create a fl oor with such flatness requires work beyond the typical standard and recommendations of the substrate trades. The tile industry flatness recommendation of ¼” in 10 feet was adapted in the past by the tile industry and published in the wood, gypsum and cement trade organization’s literature. Recent changes in the American National Standards for the Installation of Ceramic Tile (ANSI A108) call for a floor flatness of 1/8” in 10 feet when the longest edge of the tile is 15 inches or greater. This is not reflected in substrate trade documents. Unless specific requirements for larger tile are established prior to construction and then implemented, it is safe to assume there will be preparation work required prior to tile installation. It is also safe to assume there will be preparation required for any existing substrate. Attempting to correct anything other than very minor out-of-plane conditions with thinset is very labor intensive and often results in unsatisfactory installation. Floor filling underlayment products, self levelers, or even mortar beds may be required to achieve flatness tolerances needed for large tile.
Setting material manufacturers have developed many new products to aid large format tile installation. Many of these products are highly engineered to perform a specific task or tasks. In the past most manufacturers worked on a basic Good, Better, Best system. These traditional thinset products provided different levels of performance and are still adequate for many of today’s current installations. However, with current construction practices, consumer expectations, and installation requirements when using very large tile, we need to make special consideration of the type and condition of the substrate, cure time availability prior to traffic, the flatness of the substrate, environmental conditions of the job-site and the in-service use of the ceramic tile floor when selecting setting materials. Specific conditions can be accommodated with the use of highly engineered latex or polymer modified thinset products.
Seasoned tile installers insist on using traditional products they are familiar with, even if those products are inappropriate for conditions. An 18” or 24” tile has performance needs that are difficult to achieve with traditional thinset mortars. Proper mixing and application are important to realize the value in using premium thinset mortars. I have written more about getting proper coverage than probably any other aspect of tile installation. However, the message is still not being received. The dot or 5 spot method seems to be flourishing now more than ever. I was on one project that consisted of three, new car showrooms all tiled during the winter months with no expansion joints. The first warm week of spring all three buildings tented (lost bond) only a week before the owner’s inventory was arriving. While there was a host of other issues, each 18 or 24 inch tile had received six gobs of mortar. Arguably that meant perhaps 25% coverage and consequently 25% of the bond strength. However, the concrete slab was in a near polished condition, so it was going to fail regardless. The time to install increases greatly when you must trowel the floor and the tile. The suction created by a fully bedded tile can be significant and something most installers would rather avoid if they must adjust the tile, hence the preference not to do it. It is possible that a “contact” mortar may eliminate the need for back troweling the tile in some instances. But, an installer must do what is necessary to achieve proper coverage of 80% equally distributed in interior applications or 95% in exterior and wet areas. Tile is not a structural product; it is a thin, brittle, clay-based covering that must be supported.
Grout joints & rectified tile
Rectified tile is made by grinding or cutting the tile on all four sides so that measurable variance from tile to tile is minimized. (Standards for rectified tile size variation are shown in ANSI A 137.1 Table 10. Similar ISO standards do not currently exist.) One benefit of minimal size variation is that it allows for very narrow grout joints. However, variation in the substrate must be minimal as well as demonstrated in the graph accompanying this article. In the most recently published edition of the American National Standards for the Installation of Ceramic Tile (ANSI A108) minimum grout joint widths and offset recommendations were established for the very first time under industry workmanship standards as follows:
• Grout joint size.
To accommodate the range in facial dimensions of the tile supplied for a specific project, the actual grout joint size may, of necessity, vary from the grout joint size specified. The actual grout joint size shall be at least 3 times the actual variation of facial dimensions of the tile supplied. Example: for tile having a total variation of 1/16” in facial dimensions, a minimum of 3/16” grout joint shall be used. Nominal centerline of all joints shall be straight with due allowances for hand-molded or rustic tiles. In no circumstance shall the grout joint be less than 1/16”.
• Running Bond/Brick Joint Patterns:
For running bond/brick joint patterns utilizing tiles (square or rectangular) with any side greater than 15”, the grout joint shall be, on average, a minimum of 1/8” wide for rectified tiles and, on average, a minimum of 3/16” wide for calibrated (non-rectified) tiles. The grout joint width shall be increased over the minimum requirement by the amount of edge warpage on the longest edge of the actual tiles being installed. For example, for a rectified tile exhibiting 1/32” edge warpage on the longest edge, the minimum grout joint for a running bond/brick joint pattern will be 1/8” + 1/32” or 5/32”, on average. Of necessity, in any installation, some grout joints will be less and some more than the average minimum dimension to accommodate the specific tiles being installed.
• Running Bond/Brick Joint Offset:
For running bond/brick joint patterns utilizing tiles (square or rectangular) where the side being offset is greater than 18” (nominal dimension), the running bond offset will be a maximum of 33% unless otherwise specified by the tile manufacturer. If an offset greater than 33% is specified, specifier and owner must approve mock-up and lippage. These standards were created to define what can reasonably be accomplished given the limitations of clay surfacing units and dealing with the unrealistic performance expectations of end users when using large module tile products.
Over the last couple of years I have been on several projects where 18 and 24 inch tiles have completely delaminated with the thinset attached while 8 and 12 inch tile installed in different areas on the same slab with the same thinset remained bonded. Why? Shiny slabs and no movement accommodation joints! Cementious grout joint can act as a sacrificial buffer when it comes to movement. The lateral compressive force to crush a tile is in the 25,000 pound plus range. The force required to crush grout is several thousand pounds. When tile grows, as ALL tile eventually does, fewer grout joints mean less ability to absorb movement. The need for proper movement accommodation is substantially greater with larger tile. The 2011 edition of the Tile Council of America Installation Handbook included several changes. Omitting movement joints is the same as playing Russian roulette; you never know when your luck is going to run out. In my personal experience I would say that two-thirds of the jobs I look at fail in part due to lack of movement accommodation. With large tile, there is an increased importance in their proper placement.
This is only a light reading on the intricacies of installing large tile. We did not have space to devote to the latest emerging trend, large thin tile. While not in widespread use on floors, I have been on a few of those projects already too. In a nutshell, take everything I just wrote and assign it twice as great in need, which would about cover it, literally.
DAVID M. GOBIS, a third-generation tile setter, is an independent Technical Consultant. He has been in the trade for over 35 years and owned a successful contracting business for many years prior to his current position. Mr. Gobis is an Author of over 150 trade related articles and a frequent speaker at industry events. He is member of the Construction Specification Institute, International Code Council, American Concrete Institute, National Tile Contractors Technical Committee, voting member of The American National Standards for Ceramic Tile Installation and Setting Materials (ANSI A108/118), American Society for Testing of Materials (ASTM) C-21 Ceramic Whitewares, and Tile Council of America Installation Handbook committees. You can reach Dave via email, dave@ ceramictileconsultant.com