Best coverage for tile is achieved by flat troweling the thinset, keying it in to the substrate, then combing to the proper thickness in a parallel direction. Tile should be placed perpendicular to the ridges and moved slightly back and forth several times to close the ridges. Photo courtesy of Ardex.

This cracked tile could have been avoided if the tile were properly supported. If troweling alone is not sufficient to achieve proper coverage due to the tile backing, flat troweling the back, called back buttering, may be necessary.

I grew up learning how to install with just sand and cement. Thinset was still a relatively new product as was liquid latex. There was no such thing as dry polymers. Our installations were primarily deck mud on the floor and fat mud on the wall. With both, we used either Portland cement paste or the newer unsanded thinsets. Often both floors and walls were set “wet,” where you are installing tile on freshly placed mortar. Tile installation was all about “beating in” the tile, where coverage was achieved by forcing the tile into the wet mortar with a cement paste. If you look at older floor installations lippage was relatively unheard of as all tile had to be beaten in, typically with a block and mallet, and thus was always flush to the adjoining tile.

 Sand and cement installations were simple yet very effective and always provided a very flat floor. There was a skill level required to achieve successful installations. If you were not trained and skilled in the use of sand and cement you could be relatively sure the floor or wall would not last long enough to collect the check. I have read publications back into the early 1900s and even then, adequately skilled tradesmen were in short supply. This played a big part in the slow growth of the tile industry. Lack of qualified labor, hence, very expensive labor was the norm. This served as an impediment to growing the tile industry. With the desire to grow, necessity being the mother of invention, thinset was born. No longer was a 4-year indentured apprenticeship necessary to learn the basics of ceramic tile installation.

Thinsets were first developed in the fifties and sixties. Both the Tile Council of America and Henry Rothberg Sr., founder of LATICRETE International, held some of the original patents. In a short period of time, from after WWII, when all tile was mud set, to around 1970, when thinset was very common, the U.S. industry grew from 25 million to 250 million feet. The development of thinset removed the skill set required to work with sand and cement and started to make the installation process part of a knowledge rather than a skill quest. Sand and cement can be used anywhere adequate support exists; not so with thinset mortars. Some work well inside, some outside, and some but by no means all, both. Thinset may all look like sand and cement to you but the reality is those two basic components are only a small part of what’s in the bag. Thinset products have grown in complexity from the original concept of bonding to porous masonry surfaces. Current installation needs have us bonding to a wide variety of surfaces under numerous circumstances.  Hence today’s tile products and installation environments often require a much higher level of performance. There are almost an overwhelming number of specialty thinsets available today tailored to meet a specific need.

Hard to say for sure what happened here but there is not a trace of thinset on the tile, which leads me to believe the thinset skinned over prior to application of the tile. Given the soiled mop water on the thinset, I would say it lay there some time before coming loose.

So why do we need all these products? Life was simple when we only dealt with 4 ¼” wall tile, 6 x 6 quarry tile and the occasional 8 x 8 button back glazed floor tile. Today the tile is bigger, a lot bigger. Most is also low in absorbtion, which together means bonding challenges and extended cure times.  Many of the more popular and inexpensive polymer formulations have longer drying times of days instead of hours when used with large unabsorbent tile. Think of a liquid sandwiched under a layer of glass with no escape. A “gasket” of material forms at the outside edge giving even more resistance to drying or “coalescence.” Perhaps the easiest way to imagine and demonstrate this concern is to take some Elmer’s Glue or a similar product and place it between a piece of glass and a concrete block. When the glue turns clear, the polymer has coalesced and is ready for traffic. Don’t be surprised if it takes 3 or 4 days. That’s not a totally fair demonstration, because the hydration process of the cement would cause a faster set, but it is a dramatic visual. Large unit porcelain tile makes curing times more challenging. Newer formulations and specialty products are chemically enhanced to create a much faster drying time despite the large size of some tile.

How about spreadabilty and coverage? Installers have long been known for watering down thinset and grout to get the consistency they like. Watering down thinset has a dramaticly negative effect on the bonding capabilities. I was recently on a job where the thinset was poured into a pile under the center of each 24” tile which was then nestled flat to the adjoining tile. The result was loose tile and a lot of broken edges.

Regular thinset should not be built-up over a thickness of 3/8” to avoid shrinkage. Medium bed mortars allow for a thinset thickness of up to ¾”.

Putting in big tile and keeping it flat on the floor is definitely some work. There is no magic cure but there are many aids in both bonding materials and tools that make life much simpler. Some of the newer thinset products on the market go down almost as smoothly as troweling ball bearings and still support large, heavy tile. You cannot truly appreciate the benefits of many of these newer thinset products unless you have an opportunity to try some. Maybe it is because I am getting older, but easier spreading makes the day so much more enjoyable. I don’t look forward to lugging those 40-pound tiles though.

Another big bonus of some newer thinset mortars is the contact or coverage they provide. It would be hard for most to disagree that coverage is second only to lack of movement accommodation in the most readily identifiable installation issues causing failure. I think most people grossly underestimate the importance that good coverage plays. There are many new “contact” mortars on the market that truly take most of the challenge out of that very elusive and all important uniform coverage. As a contractor, the goal is getting the best possible job done in the least amount of time while dealing with less than ideal conditions whatever they may be. There is almost certainly a product designed for all those conditions worth seeking out.

All this is wonderful; things are good and getting better product wise. BUT, there is a caution. As hard as one may try, there are only so many things you can do with chemistry and engineering. In the end all of these wonderful developments are useless if one does not read and follow the instructions using good work practices. I did not want this to be an article where I harped on getting coverage and using the proper movement accommodation joints. As a contractor, I walked the walk. As an educator, I tried hard to educate using knowledge rather than simply providing instruction on procedures. Now, as an inspector and consultant, I have many opportunities to observe first hand the damages caused by failure to follow instructions and use common sense. We are now in a business where knowledge is as important, if not even more so, than the skills needed to properly install ceramic tile. With the proliferation of tile products and materials used to install them, we are approaching the point of having to be a tile geek to be an effective and profitable installer. Things being slow like they are, now is the time to avail yourself of every possible opportunity to learn more about tile and the products we use to install it. This slowdown will not last forever; there is a lot of work coming our way in the future and it is still true that cream rises to the top.