TCNA — Ceramic Tile News

TCNA - Ceramic Tile News

Ceramic Tile for Geniuses and Dummies

Presented by Robert E. Daniels, Executive Director Emeritus of TCNA

(Updated September 2005)

Originally we thought of titling this session CERAMIC TILE FOR DUMMIES to pick up on the latest book title craze. However I felt that no one would admit to being a ceramic tile dummy and there would be no attendees. We hear it all the time: My father (uncle or cousin) has been in the business for 50 years and he always did it this way, and taught it to me. It must be right. Or: I know what I’m doing and don’t need any more information.

Is this true? Are you a dummy or a tile genius? Probably, if you are human and in this business you are somewhere in between. You have some knowledge but could use some more. I have been in the tile business for over 15 years and every day at work, something new comes to my attention. You can never learn enough. Even if you rank an eight or nine out of ten on the knowledge scale, you can bet that something new is coming along that requires further study.

Have you ever gone into a floor covering store, a tile outlet, or a big box store and met the super salesperson? The one who says: Sure you can tile over Oriented Strand Board (OSB). I do it all the time. And sure, throw down a sheet of Luan underlayment that’ll level your floor real well. Caulk, what is that? I never caulk any joints, they don’t look good and aren’t needed anyway.

Then is the Interior Designer who says: I don’t care about the specifications, I just want the look. I don’t want any control joints, they spoil the look. Do these things sound like they’re coming from a genius? Maybe if the consumer hears them they have to accept these statements as facts because these are the experts!

How about the self-styled tile gurus on the Internet, or who write handyman columns, or magazine writers who intermingle fact and fiction, or even (yes) even some speakers at seminars? I hope not this one. Yes these examples are all real world examples.

It would be impossible in one 45-minute session to educate an audience in all facets of ceramic tile from the factory to the installed product. My intention is to briefly discuss the areas that most frequently come to our attention. Many of the installation issues have been, or will be covered in detail in other sessions at Coverings. I hope that you have been using your time wisely to educate yourselves by attending those sessions.


Ceramic tile itself can be a complex subject. Let’s slice down the layers of complexity and make it simple. There are two major types of tile, quarry tile: that is tile that is made by extrusion from natural clay or shale and tile that is made by the pressed dust method. This category includes wall tile, mosaic tiles, and floor tile. Either type of tile can be glazed or fired as unglazed. Glaze is a ceramic surfacing material that is used to provide a certain appearance. Let me restate this point: any ceramic tile type may be glazed or unglazed. This includes porcelain tiles.

What are porcelain tiles? They are tiles with a water absorption less than 0.5%. How can a tile absorb water, you ask? It is a dense body of minerals that is heated to a high temperature and is not like a sponge. The answer is that it can. One dries a tile then weighs it, soaks it in water and then measures it again. The weight change represents the % of water absorbed. (Weight after soaking minus weight when dry divided by weight when dry is % water absorption.)

Water absorption of tile is controlled by the selection of raw material used for the body and the manufacturing process. It is the body that absorbs the water not the glazed surface. (In fact the glaze may be sawed away from the surface while running the test.) The water absorption determines the classification of tile. Wall tile has from 7-20% water absorption (that’s right, it’s a lot). That’s why you shouldn’t use wall tile outside where there can be freezing temperatures. The water goes into the body when it rains, snows, from pools and fountains, and even condensation, and then it expands when it freezes and the tile cracks. So don’t put this tile outside in most places in the U.S. Even Florida and California have some freezing days in most parts of the state. The same holds for Saltillo tile that rough looking hand pressed Mexican tiles. These can have water absorption up to 30%.

Wall tile is made for a purpose, sticking on a wall (although it can be used on countertops and sometimes on floors. It requires beauty as it is frequently at eye level, or near one’s field of vision. The size must be close to uniform as it usually has a small space between each tile (called a grout joint). The relatively soft body of wall tile makes it easy to cut to fit (including round holes for plumbing fixtures) and helps the tile to stick to the wall without sliding.

Is it a good idea to use tiles that can absorb 7-20% water (usually they absorb about 12-14%) in wet areas? Well actually the surface glaze is impenetrable to water and acts as a barrier when this tile is used in bathtubs, showers, pools, and elsewhere where there is water. Water will penetrate the grout joints no matter how careful the installer is. This means that some method of protecting the underlying backing material needs to be used, in wet areas, such as a liquid or solid water-proof membranes or waterproof materials (i.e. cementitious backerboard).

It should be mentioned that, although any tile can be glazed or unglazed, unglazed wall tile is not a commonly used product as it absorbs too much water and was made for decorative effect in the first place. Floor tiles (pavers) are tiles made by the pressed dust method and can have water absorption from zero to five percent. They have lower water absorption than wall tiles because they have a denser body. They must be strong enough to walk on and therefore require this stronger body.

You may ask at this point, how can a pressed dust body produce a strong tile? Dust isn’t very strong is it? Well, this process is one in which the mineral components of the tile body are milled to very small particles (like dust) and then pressed under very high pressure to form the tile body. If all the particles are the same size and very small, they will compact into a strong body that when heated in a kiln will fuse into a strong, dense, and low water absorbing body. A small amount of water is left in the body during pressing to help hold the body together (about 5%, if you are into details). Then the tile is dried to about 2% water before putting it into the oven (lovingly called a kiln). Most tile today is single-fired. That is, it goes through the kiln once. So if it is to be a glazed tile, it is glazed after drying and then fired to h a high temperature (over 2000 degrees Fahrenheit).

Glazing today is a very sophisticated matter. Modern high volume plants have a plethora of devices on a conveyorized glaze line, such as silk-screeners, waterfalls, sprays, dry glaze dispersers, printing rollers, texturizing machines, and other devices. Some factories have 15 or more applications of glaze material on one line before firing the tile. Why? To make the tile look natural and random. It is harder to replicate nature than to make a regular flat-colored glazed tile. It’s not nice to fool Mother Nature is it?

Quarry tile has water absorption less than 5% too. When it is extruded, a dense surface forms that reduces the staining and surface porosity of the unglazed tile (remember all tile can be glazed). It can be made very thick and therefore strong. This makes quarry tile a good candidate for warehouses, fast food places with high traffic, commercial kitchens, dairies, meatpacking plants and other areas where strength and ability to clean are paramount. If it is used unglazed (which it generally is) it doesn’t have a thin surface to wear out and will last a very long time.

And now for the tile of the moment: Porcelain Pavers. This is probably one of the most misunderstood products based on our current telephone traffic and written information being published. Simply put, this is within the previously mention paver category but is tile that has water absorption less than 0.5%. This is very low and that makes these tiles very strong and dense. Because they are so dense that they can be left unglazed and used on the floor. If so they have no glaze to wear out and therefore will stay the same color and look for a very long time, maybe thousands of years and long enough that we don’t have to worry about this anymore. Because they are the same color through out the body (through-body tile) they can be polished and ground to size just like stone. Grinding can make the size and geometry of the tile very precise and permit narrow grout joints.

Let me interject a word about grout joints. Grout is used to fill the space between the tiles. The current tolerance for tile size permits a fairly wide variation in the actual body size (ANSI A137). Pavers can vary up to 3% and still be classed as standard grade. The new ISO standards have reduced this to plus or minus 1% but on a twelve-by-twelve tile this is plus or minus 3mm (a little over 1/10 of an inch). If one tile is bigger and one is smaller that is a range of 1/5th of an inch. The purpose of the grout joint is to allow for this potential size variation. Manufacturers can sort the tile into size ranges (called caliber) and mark the box accordingly. You then need to remember to use one caliber on a job. Still the sizes will vary from tile to tile and a proper width grout joint must be selected.

But wait a minute; if these porcelain tiles are so perfect why not use them everywhere? Well, there are some consequences of making a tile with near zero water absorption. First of all, it is harder to get adhesive to stick to the tile. Wall tile with its high water absorption will grab into the adhesive fast and stick well to a vertical surface. You can use porcelain tile on a vertical surface but it needs to be physically supported while the adhesive sets, for example with plastic spacers or boat rope. We recommend using the best adhesive available for these tiles, latex modified thinset or epoxy.

Second, this tile is harder to cut. Your grandfather’s snap cutter or carbide blade will be challenged when cutting this product. You need a diamond wet-saw. While on this subject and in case you feel like going home to set tile tonight, do not under any circumstance use a dry blade in a power saw to cut tile or any other product that contains silica. The watchdogs at OSHA are developing standards for exposure to silica dust as I speak to you. It’s not as good idea to breathe this stuff even if the medical science is still being evaluated.

Third, even with low water absorption, because the surface may be unglazed, there is a surface micro-porosity (real little holes on the surface) that can allow staining. Not good if you drop ink on your floor. The manufacturers are solving this by adding a clear glaze to the surface of the unglazed tile.

Fourth, up to now the color ranges and finishes of unglazed porcelain pavers has been limited and considered more of an institutional look. This too is being addressed and many new styles and colors are coming into the market.

Back now to glazed pavers. These can have low water absorption, as low as zero, but generally the manufacturer makes them with 2-3% absorption in order to improve the bonding, and ease the cutting operation while still providing adequate break-strength and frost resistance. Yes, these lower water absorption tiles from zero to 5% can be used outside even where it freezes.

We have not yet discussed mosaic tiles. What are they? They are small porcelain tiles that can be either glazed or unglazed, and I won’t say that again, I promise. They are less than six square inches and generally are sheet-mounted at the factory to save time in installation. Who wants to put little one by ones in a 40,000 square foot shopping mall piece by piece? They are strong and have low water absorption and have some real advantages.

Because they are small (about 2-1/4 by 2-1/4 maximum) they will follow a contour such as in shower floor. They allow for many drainage channels in wet areas to improve the slip-resistance (more on this later) and they provide for many geometric designs. They recently have become quite popular as accents to larger tiles. If they are left unglazed, they will last for a very long time.

And now to the finishing touch: glaze. Glazes are a thin finish that can and will eventually wear off of the tile. Selection of the area of use for different glaze ratings is important. Currently the industry is using the following glaze wear rating system (as is ISO, the International Standards Organization and most of the world):

0 — Decorative tile only (look but don’t scrub)

1 — Non-traffic area tile (put it on the wall)

2 — Light traffic (like in the bathroom with slippers and bare feet)

3 — Residential inner rooms (kitchens, sunrooms, etc)

4 — Light commercial (office buildings, showrooms, entry-ways)

5 — High traffic (shopping malls, fast food, etc.)

Finally, a lesson on coefficient of friction (COF) and then I’ll slip out of here. There are no national standards or requirements for coefficient of friction. There are some local municipalities that have building codes, however. The American’s with Disabilities Act (ADA) recommends a COF of 0.6 or greater on flat surfaces and for people with disabilities and 0.8 on ramps and inclines, but there are no laws, standards or whatever specifying the COF.

Furthermore, the method of measurement must be specified in order for this to have technical meaning. In the US, we use the ASTM 1028 sled method where a 50-pound weight is placed on a sled with a special material (to represent a shoe sole) contacting the tile and it is pulled by an operator using a fish-scale. It is a dry measurement although it can be performed wet with water for investigation. The pull force needed to just start the sled moving, divided by the 50-pound weight determines the COF. Example: if it takes 30 pounds of pull to start the sled, divide this by 50 and you get 0.6, just enough for the ADA recommendation.

But after the tile is installed, it must be kept clean. Ceramic tile is water resistant and stuff stays on the surface such as water, grease, banana peels, and other things too gross to mention. So the spills need to come up fast and the water needs to be removed or the COF goes down. Tile can be made very slip resistant but then it is harder to clean. A judicious choice must be made when selecting tile.

Time does not permit further discussion about tile and we have not even touched upon installation. The majority of phone calls that we get concern installation. That’s where the rubber meets the road and detailed training is required.

The standards used in the US are the ANSI A108/118 for installation and the A137.1 for tile itself. The TCNA publishes both of these along with the Handbook for Ceramic Tile Installation and they are available from our office and here at the show. Give us a call at 864-646-TILE (8453) for more information and we’ll do our best to make geniuses out of dummies.

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