Installing Large Format Ceramic Tiles
January 17, 2012
Already big tile is getting even bigger! I don’t know at what point if any the term “tile” should be used when they get to be half the size of a sheet of plywood. Rest assured; as the economy picks up we will be seeing more. The recent Cersaie exhibit featured a plethora of new finished looks for tile, many being available in very large modules, some up to 4’ (120 cm = 47.25 inches) in size. Due to rapid advances in technology, tile has grown in size and finishes more rapidly in the past 30 years than the past 2,000. These same advancements are also responsible for a brand new category of product, thin tile. Some porcelain is now offered as thin as 3 mm (approximately 3/32”). The accomplishment of this revolutionary product was created by tweaking the components used in ceramic tile with use of a more advanced manufacturing process. The basic mineral components and a manufacturing process that formerly took days to produce ceramic tile and in a limited size range now takes less than an hour, and seemingly packaging and transportation pose the only limits to size. There are plenty of installers who run for cover when asked to install extra-large tile modules. Then again there are those who stay and should have left. Getting these in right requires exceptional resolve on the part of the installer.
The marketing hype on all the advancements in tile style and new production abilities certainly have the ceramic tile sales and design community whipped up into frenzy on these latest offerings. Nearly all want these new products put in at every opportunity so they and their clients can show their forward thinking and be on the cutting edge of fashion. When these products are specified, the installation community wonders how they are physically going to install these huge pieces of tile including the proper preparation and bonding material. With shrinking profits, inadequate and unrealistic time constraints imposed by construction “managers” or GCs, that can be challenging. It becomes more so with the lack of formally trained installation staff in using the latest installation products and techniques. It is easy to understand why a seemingly growing amount of end users voice concerns over aesthetics and performance issues on completed projects as contractors struggle with the conditions required to properly install these monoliths of tile.
When it is large somebody really needs to take charge and create an awareness of the challenges and requirements so all affected parties can realize their goals. The days of a few hours floor prep, if any, using a bag of the cheapest 118.4 modified thinset to install and grouting the next day are not an option with big tile. The considerations for all tile installations are similar, but the bigger the tile the less tolerance for anything short of excellence in the entire installation process. What follows is my view of a few areas that somebody needs to specifically address in the installation process.
Floor prep is at number one when you’re doing big tile. There are several areas which require higher than normal consideration. Tile is a finishing material with no structural value. Most of the wood structures built today use engineered floor joists. This has been a vast improvement in support and creates flatter floors when properly installed. In the days of dimensional floor joists it was always “point the crown up,” which leads to a number of occasions where anything bigger than a 6” x 6” was going to require a reinforced mortar bed due to swales in the floor. This concern has not completely disappeared with the use of engineered floor joist systems but it is better. Unfortunately, under the current practice of building a structure to minimum code requirements, the mortar option is not available. The weight of the mortar bed cannot be adequately supported unless part of the structural design load or substantial expenditures are made to reinforce the existing floor. It never ceases to amaze me how many jobs I go out on where someone has no idea of what the underside of the floor looks like or what the load rating was before the now-failed tile was installed.
Whether concrete or wood, the structure must be rated for both the type of use it will receive and the finished weight of all materials used in the installation process to insure it is capable of providing adequate support. Flatness is perhaps the most vexing costly issue a tile installer faces when using large module material. Recently there were some changes made to the substrate requirements for ceramic tile under the American National Standards ANSI A108.1-184.108.40.206 which says: “For tile with all edges shorter than 15”, shall have a maximum permissible variation of ¼ in. in 10 ft. (6 mm in 3 m) from the required plane, and no nor more than 1/16 in. variation in 12 in. (2 mm in 305 mm) when measured from the high points in the surface. For tiles with at least one edge 15 inches (381 mm) or longer, the substrate shall have a maximum permissible variation of 1/8 inch in 10 feet (3 mm in 3 m) from the required plane, and no more than 1/16 inch variation in 24 inches (2 mm in 610 mm) when measured from the high points in the surface. Alternatively, in lieu of these tolerances, the concrete slab can be depressed to accommodate a mortar bed method of installation.”
Unfortunately the title of the American National Standards ANSI A108.1 is: General Requirements: Subsurface and Preparations by Other Trades. These new 1/8” tolerances are not currently a required part of the gypsum, concrete or wood trade recommendations. Hence in new construction, someone needs to verify if the substrates trades are willing to prepare the floor or wall properly or who will be responsible preparation and payment, if required. In remodeling, that is a responsibility you accept if you’re the only contractor on the job. As we all know, setting material manufacturers are more than happy to provide us with the appropriate remedial products. The problem is and always has been getting paid to purchase and install them. That part is getting worse, not better.
Once the floor is properly prepared, cleanliness is next to godliness and as always, nothing sticks to dirt. I have seen on occasion where the dirt was turned to mud; that didn’t work out so well either. Thinset definitely does not bond to paint overspray. Recently I was at a home where the owner had expressed concern to the building contractor that the interior deck of his home was getting excessively wet and delaminating due to continual delays in getting the roof on. The contractor then sprayed a wood waterproofing agent on the floor which stopped the panel from absorbing moisture, but also prevented the tile membrane later placed over it from bonding as well.
The biggest substrate issue I see by far is shiny concrete slabs. A slab is shiny for one of two reasons. It was either over troweled or had a curing agent/sealer applied. Tile floors require broom finish concrete once troweling is complete with no curing agents. This is alluded to in the concrete industry documents, so there is a responsible party. Somebody needs to make sure that if the slab is not broom finished, it is otherwise properly abraded by mechanical means by the appropriate party. Without going into a complex subject, I can assure you, the bigger the tile the greater the importance of being able to securely bond the tile to the substrate with the appropriate mortar.
When projects are loosely specified by an architect or manufacturer with such basic terms as “thinset mortar must meet ANSI A 118.4,” things can quickly degrade to a point that even the famous “value engineering” would not allow. When not under architectural control and looking for places to save and submit the lowest possible bid, some mistakenly think thinset is one of those areas that won’t make that much difference. It is easy to understand why. For many years cement based thinset mortar was either modified (118.4) or unmodified (118.1). The only changes since those original standards were created was the addition of a thinset recommended for direct bond to plywood, ANSI A118.11. Thinset mortars have continued to grow in both numbers and complexity. A fair number are designed specifically to work with large tile but there is no way to specify them. In checking various manufacturer product lines you will typically find 2 or 3 ANSI 118.1 mortars, 15 to 20 118.4 mortars with some meeting 118.11 as well.
Even the most studious tile person often has trouble distinguishing one mortar from the next, but there is a different product performance criteria for each and every product made. Unless you are very technical and uncommonly learned, it is likely you would have to ask the reason why you should use one over the other as they all meet ANSI A 118.4. Using base grade (the cheapest) products for installing large tile is an inherently bad idea on a number of fronts. Bigger tile has less flexibility than smaller tile, so thinset with high bond strength and greater deformation abilities should be common sense. Thinset under bigger tile takes longer to dry. There are no special cements or other types of chemicals that promote rapid drying in base grade products. What may dry under an 8” 3% absorbtion ceramic tile in 24 hours may well take 3 days under a porcelain tile, and it certainly would not be anywhere near ready overnight.
Somebody needs to be able to explain the difference so proper products may be used and compensated for. Using solely the 118.4 thinset standard won’t help you much if you are trying to get a higher performance thinset specified, which can cut days off the project time and open the floor to traffic sooner. You will find much less resistance to price if you point out the performance values and time that using a premium product can save. You may want to consider using the ISO 13007 standards, which while not providing the answers to all specification, shows clearly how to specify a higher-performing product than base grade.
Movement joints are still my soap box issue, though others are gaining ground. As I enter my fourteenth year of taking technical calls and fourth in looking at job problems full-time, they remain at the top of the list in either causing or contributing to tile installation failures. Nary has a day gone by where I don’t get that phone call. It is likely responsible for half of my income. I get in planes and fly all over the U.S. to look at problems, when I know the cause before I even pack my bags, as soon as they say loose tile and tented floor. But before some poor soul (not always an installer, but most of the time) loses copious amounts of money for his errors, you must actually see the job. To know the reason without having physically observed it is considered heresy in the judicial system and has no legal standing in court.
I could probably fill half this magazine with wallet-sized photos of tented floors and I am just one person. You need the joints; history and experience tell me the bigger the tile, all else being equal, the more you need the joints. If the customer wants a 1/8” grout joint, you need twice as many joints. Minimum movement joint width is ¼” every 20’-25’ except in wet areas or those that receive direct sunlight which require 8’-12’. A 1/8” joint at half the distance in either situation would be a suitable option to me as long as they were properly constructed. There should always be a ¼” perimeter joint. Out of all the things you do on a job, in my opinion, proper movement accommodation has the greatest importance. If you’re a little light in other areas, you will at least have a chance if the tile has a source of movement accommodation.