Normally we attach backer board to the wall or floor. For this one, we are attaching to a plate glass window. A funny thing happened as it dried: it turned into a 3-foot-by-2-foot coffee saucer. Shrinkage is common and can become excessive when building up with the wrong thinset mortar or any build up under glass tile.
Back when this article was scheduled in the early part of 2005, I was sure that by this time of the year I would have had time to use all the new products introduced. A funny thing happened along the way: they kept introducing new products and revising old formulas. I have read some glowing articles on all the progress that has been made with setting materials from nearly every manufacturer. So, not that it matters, but what is my verdict? Outstanding, with reservation. A few years back I wrote an article called "Thinset, It's not Just Sand and Cement Anymore." Guess what? Now the sand is gone too in some instances! It is replaced in some instances by tiny glass spheres. Thinsets have become highly formulated for very specific purposes. The old stand-bys for the most part have remained intact but new materials have given us the ability to go places we could not go before, such as installing green marble with thinset. Membranes for various applications are being heavily promoted along with new grout formulations.

So what does all this mean to the average installer? It means you better start reading up on things. Around my old shop the saying used to be these setting material guys must think we are chemists. That was when manufacturers were averaging about 10 different types of products each, not the 30 typical of most manufacturers today. Do you really need to be a chemist? No, but you do need to follow the directions about mixing water, temperature ranges, drill speed, and working time. Gone are the days when you can adjust your thinset with water to suit your needs. The 20 or so thinsets we have on hand here range from 4 quarts to 8 quarts for a 50-pound bag, which is chemistry at work. Of course then again, in one instance we have 50 pounds of coverage in a 25-pound bag with 6 3/4 quarts of water and up to a 3/4-inch notch trowel; now that is a lot of chemistry. This chemistry is all about making your job as an installer easier in spite of the outward appearances. Much has been written about "regular" thinsets. Let's take a look at some of the pluses and possible minuses of some of these newer setting materials.

Once the proper thinset is selected for the application, it is all about getting enough coverage. Over the last few years many new notch configurations have been introduced that assist in obtaining adequate coverage.

Light-Weight Thinset

This is new technology to the United States. The sand has been replaced with a light weight aggregate, with recycled glass spheres reducing the weight of a 50-pound bag to 25 or 30 with no change in coverage. The products we have on hand here have their own handles built in the bag and provide an ease of handling I have always dreamed about. Because they are premium products they also have some impressive bonding strengths and flexural values. The ones I have tried are also very good on vertical surfaces; there is virtually no slip with very little effort.

Contact Mortars

When you look for something easy to spread it doesn't get any better than this. If you have a lot of large unit material to install getting the needed coverage can be much easier. When placing a tile across the ridges and giving it a little back and forth motion a process starts where the thinset actually spreads itself out. If there were a down side to using this product, it would be that the floor needs to be flat. Tile setters seem to have a habit of adding a little extra to the back to make up for inconsistencies in the floor when they should really prepare it prior to setting. If this is a habit you have, contact mortars are not for you. Large tile requires a flat floor and contact mortars should only be used on properly prepared substrates to avoid sunken tile the next day.

Using a 1/4-inch-by-1/4-inch trowel we checked coverage on 4 different sized tiles. It becomes very apparent that as the tile grows so should the notch.

Medium Bed Mortar

While not particularly new they certainly are not used as much as they should be. We continue to see installers trying to build up floors with less expensive thinset. A regular thinset is not designed for thickness over 3/8-inch roughly speaking. When used in this type of application excessive shrinkage can result in cracked tile and stone. Most medium bed materials can be used up to a 3/4-inch thickness. If your application of medium bed thinset is over an impervious waterproof substrate you may want to consult the manufacturer when using it to install soft or pours stone as warpage can result in some instances.

Looking closely at the notches you can see they are various sizes. If you compare to the other picture in this article you can see what a difference some variation in notch configuration has made in obtaining good coverage.

Water Sensitive Stone

Green, black and red marble along with some concrete tile can be very sensitive to moisture in conventional setting materials. In the past epoxy was our only choice. There are several new products on the market formulated to use all the water in the setting material preventing potential warpage.

Common sense should dictate that when using impervious tile, especially over an impervious surface, drying time will be extended. But, will backerboard over a wall stud affect drying? Here it is! It has little relevance to real world installations but does make you think how particular thinset has become.
There are also a few fast drying products recommended for these types of installations. It only takes one bad concrete tile or marble tile job to provide a lifetime of conversation on what not to do. Mine was about the cost of a 4-year degree.

Using the same notch as in our multiple size tile picture, we made a swirl patteren instead of using directional troweling. It is very apparent that air became trapped in the swirl marks and prevented the tile from seating in the thinset.

Glass Tile

Nope, there's no magic bullet here. While it may be the wish of many, there is no consistent answer here. There are many types of glass with almost as many properties. It is very important to consult the manufacturer's written instructions. With the variation of both products and in some case backings, there is no rule of thumb here nor setting material that will perform in every instance. With large unit glass tile I would not even consider installing it without a specific recommendation. We see a lot of installations issues here relative to the amount of product sold. Large unit glass is especially unforgiving of poor preparation and irregular substrates. 100 percent coverage evenly distributed in a thin even layer is the key to success once the right material has been chosen for the installation. No matter how technical you want to get or how much money you're willing to spend on setting materials, if you don't get enough material on the back of any ceramic tile, it doesn't matter. Included in this article are some pictures of trowels which may appear odd looking to some of you. Many speak of back buttering as the only way to achieve 100 percent coverage on a consistent basis. There can be no argument that back buttering tile is a good thing. But, what if there really was an easier way? If you have not tried some of these newer notch configurations you owe yourself a favor, buy one, or two. I am confident you will have found an easier way to install all but those with the roughest backs on ceramic tile.