Expert Guide on Ceramic Tile

Disclaimer:  Tile training information is seldom straightforward and can be confusing.  Advances in technology have seemingly outpaced the updating of training information available, creating a large gap in complete tile knowledge and the spread of misinformation.  To make matters more confusing, some standards for tile differ from country to country, making terminology no longer universal.  For example, China has been known to classify products as porcelain with a higher water absorption rate than .5%, which does not conform to American standards.  As you sift through learning about products, be wary of blanket statements that may be misleading.  Phrases that generalize products without market vertical context, such as “porcelain is generally more expensive than ceramic” are misleading.

Welcome to part 2 of the late May published Blog, where I reviewed Basic Tile Information In the Age of Misinformation. I promised a follow-up with greater detail, so buckle up for more information on ceramic tile than you bargained for.  This blog will review in great detail different types of ceramics, pulling together a robust mix of ceramic tile product classifications, broken down in multiple ways, and map the recent evolution of ceramic tile.  The focus is on the chart I created and is my attempt to find a different way to educate all tile industry stakeholders on information that is not readily available. That also means I will try not to include information easily searched on the internet. 

On the residential side, you may find more helpful information in our previous blog, mentioned above, with broader tips on how to navigate your shopping experience and align your lifestyle alongside the proper selections. Commercially, this blog may be more your cup of tea - or should I say Italian espresso. Regardless of which sector your tile project lives in, I will do my best to make this blog relevant for both, just as a large portion of products are suitable for both. For ease, let’s break up this tile information into 3 parts:

Part A:  Ceramic Classification Related to Porosity & Kiln Firing Rate

Part B:  Material & Product Sub-Classifications 

Part C: Porcelain Innovation from the year 2000 and Beyond

Let's kick it off by defining the term "Ceramic." Ceramic tile is a ceramic surface component, usually relatively thin in relation to facial area, having either a glazed or unglazed face and in the course of manufacture, fired to a temperature sufficiently high to produce specific physical properties and characteristics. 

PART A:  Ceramic Classification Related to Porosity & Kiln Firing Rate

Ceramic tiles are classified into four categories based on the weight of water absorbed as a percentage of tile weight. Porcelain is the only product that neatly fits into the impervious category. Other types of ceramics fall into the other groups based on porosity rate, which differs from product to product, even within the same manufacturer.  In Part B coming up next, you will see that these porosity classifications create the groups for each material product category.  That’s right - not all material categories are created equally. Before getting to the categories, let’s hone in on some details of Part A:

Vitrified - When the mix for a porcelain tile (such as silica and sand) is fired, it vitrifies due to the high temperatures. Vitrification (from the Latin vitreum, “glass” via the French vitrifier) means to become glass-like or to be transformed into a non-crystalline amorphous solid. Ceramic tiles are more like cement, in that they’re porous and less suitable for wet environments. Porcelain tiles are fired at a much higher temperature than ceramic causing the tile to become fully vitrified (.5% or less water absorption). In reality, all ceramics are vitrified to some extent and the vitrified classification can often be confusing. It helps to see the diagram below, where the number of “air pockets'' in each classification is a visual guide to show that more air pockets = more moisture. 

Indoor Wall Tile 

Non-Vitreous = Tiles fired at a low temperature, often for a short period of time. Non-Vitreous tiles are highly porous (>7% water absorption), and are not frost-resistance, making them suitable for indoor walls only, hence the highest number of air pockets.

Indoor Wall & Floor Tile 

Semi-Vitreous = Tiles fired at the same temperature as non-vitreous tiles however for a longer period of time. Semi-Vitreous tiles absorb between 3% and 7% moisture, and are not frost-resistant, making them suitable for indoor walls and floors.

Indoor & Outdoor Wall & Floor Tile

Vitreous =Tiles fired at very high temperatures for a long period of time.  Vitreous tiles absorb 0.5-3% moisture and are suitable for indoor and outdoor installations in non-freeze/thaw temperatures. Tiles on the lowest side of the water absorption scale, which absorb a mere 0.5% meet the minimum threshold to be classified as Porcelain. However, outdoor suitability is determined by the tile manufacturer as slip resistance takes into consideration surface texture, climate, traffic level, and more.  

Impervious = Tiles fired at the highest temperature and for the longest period of time. Impervious tiles may have some additional key ingredients (tile recipes are generally not public), which result in a porcelain product that absorbs ≤.5%, making them suitable for indoor and outdoor areas in all temperatures, hence the least number of air pockets.  

The last thing to review in Part A is the difference between Bicottura and Monocottura.  You may have been a tile industry ally for many years before hearing these terms - or perhaps they are new to you.  These terms are related to how many times a tile is baked or fired in a kiln.

Bicottura is an Italian term given to tiles with special glazes and designs that require two or more firings. Bicottura tile is approximately 1,500 yrs old and is the best production method for decorative tiles that require multiple colors.  Most Bicottura tiles are for indoor applications such as backsplashes and are more expensive due to the longer production time, glazes used to produce high color & designs, and artisan skills.  The low firing temperature results in a higher water absorption rate and a softer body.  This type of tile is usually made to order, priced higher, not stocked locally, and can have a long lead-time due to extra steps, possibly not mechanized, in the manufacturing process. Some Bicottura tiles are fired 5x!

Interestingly enough, the 2nd+ firing is not always in the same kiln. In our Kiln & Penny Collection, the 3x12 Metal Inserto Deco is actually transported within Italy to a small-batch artisan studio, where the design and glaze are applied and baked a 2nd time, before going back to the main factory.  As with all artisanal goods, these products are priced appropriately given the required skill-set and logistics necessary to create them.

Monocottura is an Italian term given to single-fired tiles, which is the most common and economical method. The largest umbrella of products on the market is Monocottura and this tile term primarily encompasses; encaustic, glazed ceramic, quarry, and porcelain.  The largest number of tiles stocked at a retailer will fall under this category. 

PART B: Material & Product Sub-Classifications

Material and product classifications & subclassifications are arguably the most confusing terminology in the tile industry. No thanks to the internet for making everybody a tile "expert," some of the definitions are not entirely accurate, hence the creation of this fancy chart. In case you're wondering at this point if all the parts make a whole, they do, and the big reveal will be at the end. 

Ceramic tile has evolved tremendously since the dark ages. Porcelain is believed to have been invented in China during the Ming Dynasty, but in the US, the evolution has largely happened since the 20th Century. This is due to the invention of the Tunnel Kiln in 1910, and then much later with technological advances in machinery and digital printing. If we ever write a historic tile events timeline blog, this date will most certainly make the cut.

CERAMIC TILE TYPES -  Part B: Product & Material Sub-Classifications

Ceramic Wall-Ceramic tiles suitable for indoor walls only are either pressed or extruded. Tiles that are not rectified are known as “pressed” with a factory edge and vary slightly in size from each production run.  Due to the slight, often unnoticeable to the human eye, size variations, 3/8” grout joints are needed to align the tile correctly during installation.  Any joint smaller may result in a floor that will be misaligned at some point during the installation. The most cost-effective Porcelain is also pressed.

Extruded tiles are formed when wet clay is forced through a mold. Think of it like making pasta with a hand rolling machine or applying icing to a cake.  Just like these foods, extruded tiles can be made by artisans in small batches, or through high-yield machinery.  

Ceramic Wall & Floor -The majority of the ceramic wall tile market, is comprised of glazed ceramic floor tile made in large scale factories outside of the USA, using the dust-pressed method. Let’s explore the main categories more:

Encaustic- Encaustic or Inlaid ceramic is a historic method of tile making first introduced in the Middle Ages. Created with an inlaid pattern of two or more different colors of clay, and then baked; inlaid tiles had striking beauty and historic installations are still intact, a true testament to ceramic durability. Throughout history and still, to this day, the term inlaid is mistakenly called encaustic.  Encaustic refers to painting or enameling using pigments mixed with hot wax that is burned in, as an inlay.  Ebbs and flows in popularity led to the Victorians eventually discovering the floors and incorrectly naming them encaustic, as these tiles resembled enamel work.  They have been incorrectly named for so long that it’s now (often) considered an acceptable term. Recently, concrete tiles have commonly been named encaustic by tile allies, adding more to the confusion.  Today, Inlaid tile is no longer mass-produced in commercial quantities, although you will find the verbiage being used to describe part of the process used to manufacture other types of tile, mainly cement.  

Terracotta - Terracotta is one of the oldest types of ceramic tile and the term means "baked earth" in Italian.  A typical body of terracotta tile is red, but can also be white.  Zellige is actually a terracotta ceramic tile, which you may be more familiar with due to its resurgence in recent trends.    

Zellige tiles are a highly specialized tiles, handmade by craftsmen. They are moulded, cut and glazed by hand, all without machines. The first step is to mix natural clay (usually from Fez, in Morocco) with water. They are then hand-shaped, dried, and kiln fired using olive pits. After being fired, enamel glazing is applied to offer protection to the tile. Zellige tiles are imperfect by design and each tile will contain pits, crazing, and imperfections due to the manufacturing process.  Zellige tiles are installed with as little grout as possible (yes grout is required) to highlight this feature. SHOP Architessa Zellige Look Collections here.

Glazed Ceramic-Tile with a glassy opaque coating, fired for hardness that forms a smooth decorative surface. Glazed ceramic is fired at a lower temperature than porcelain and has a water absorption rate higher than porcelain.  The body of glazed ceramic can be white, red, or pink depending on the origin of the raw materials closest to the manufacturer. Neither of these is superior based on the color alone, but they can be engineered to have other characteristics and are often marketed as being superior over each other.  If glazed ceramic chips, the body will show through, however, when this happens the tile will need to be replaced regardless, as a chip can be a tripping hazard and lead to more damage.  SHOP Architessa Glazed Ceramic Collections here.

Quarry Tile-Quarry tiles are not produced in a quarry as might be suggested by the name and they are not classified as porcelain due to a higher water absorption rate. They are manufactured with natural ingredients including clays, shales, and feldspar, and extruded through a die and cut. This extrusion process creates a much tighter/denser body than can be achieved through other processes. The die also creates a ribbed back on the tile to improve mortar adhesion. Once extruded, the tiles are sent through a drier and fired in a kiln. 

Quarry tiles are ½” thick, unglazed, and have the same color and texture in the body of the tile. They perform well in industrial, exterior, and heavy commercial areas, and have high slip resistance. Some quarry tile is produced with medium to high shade variation from tile to tile. This classic architectural look (sometimes known as flashing) is achieved by controlling the flow of oxygen and gasses in the kiln. Whether monotone or with color variation, all quarry tile colors have a natural look that matches well with other design elements.

Porcelain- Porcelain has its own class of products, although still technically considered a ceramic. The big differentiator (in layman's terms) is that it’s baked for longer, at higher temperatures. The firing characteristics essentially ensure the ingredients liquefy and settle into all tiny gaps and holes, enclosing them to meet the lowest category of water absorption, being .5% or less. Porcelain is denser and harder in structure, which means it is more difficult to cut, drill through, and bond.  

Rarely extruded, porcelain is either pressed or rectified. Rectified tile is a tile with an extra step in the manufacturing process, which mechanically grinds each side to achieve precise and consistent dimensions.  The most sought-after feature of rectified tile is that the uniform size allows for tile to be installed with small grout joints no smaller than 1/8”.  

Another important term to mention is Calibration. Calibration is a sorting process that manufacturers may use to ensure all tiles within packaged boxes are dimensionally consistent. In the manufacturing process, unfired ceramic tiles are nearly identical in size when they exit the press, but the firing process in the kiln will cause the tiles to shrink–perhaps at slightly different rates from piece to piece. Through calibration, manufacturers sort tiles based on the finished size. Tiles are commonly grouped into two to four different calibers based on the strict sizing requirements of the industry. Calibrated tiles are typically allowed no more than +/-0.5% variation from the average dimension of the corresponding caliber, not to exceed +/- 2mm. It is important to note that in a multi-sized pattern with rectified tiles you must use tiles that have the same calibration. Often, these things are never thought about during a selection process.  Homeowners or beginner specifiers might see a picture of a beautiful installation and never realize all the little details of the material and installation that were precisely curated to make that beautiful space. Navigating all the things that could go wrong is hard given all the choices now required to choose tile and set it with.  

Porcelain is made by the Dry-Pressing method and is further divided into 4 different tile product categories:

Glazed Porcelain - Glazed porcelain has a protective glaze of 1mm or less of liquid glass or enamel that is applied over a printed image. The body of the tile is called “white” even though it’s typically in softer tones of gray and cream and it won’t necessarily match the glaze.Glazes must be applied over all inkjet-printed tiles to protect the image as the image is underneath. Because these glazes are protecting, essentially what is a photograph, there will be a repeat within the pattern. All inkjet porcelains are glazed and we can now replicatereclaimed wood, fabrics, rare stones images, andmore– making glazed porcelain the most popular and ubiquitous. Glazed tiles are the most economical and are commonly confused with Color Body Porcelains. Glazed v. Color Body differentiation is only specified by the manufacturer, not through your senses.  SHOP Architessa Glazed Porcelain Collections here.

Color Body Porcelain - Glazed tiles with a solid-colored body similar to the surface glaze’s most dominant color.  Synchronizing the color of both the glaze and body lessens the visibility of chips.  The main tile color remains consistent throughout the tile, but any surface design does not continue through the body.  Color Body Porcelain is always glazed so referring to a color body tile, as “Glazed Color Body” is redundant. SHOP Architessa Color Body Collections here.

Through Body Porcelain - Unglazed tiles with a less smooth surface texture than Glazed or Color Body Porcelain where the surface color and body have the same pigment and pattern (albeit minimal) throughout.  These tiles are typically used in high-traffic commercial applications that require high slip resistance. Through Body tiles are produced using colored raw material that comprises the entire tile. These tiles are the only ones on the market currently with uninterrupted color and pattern on the surface all the way through the tile body. During the firing process, sintering occurs making the tile one. Surfaces made of pressed pigments are easy to clean, more scratch-resistant than glazed tile, and harder than granite. This type of tile is also referred to as “Unglazed, or Full Body” and its biggest limitation is the designs available as they consist of solid colors and simple patterns.  SHOP Architessa Through Body Collections here.

Double Loaded Porcelain - Double Loaded Porcelain uses a mix of raw materials infused with color pigments pressed to the base layer and put under high pressure to make a thick layer of design.  It has a different face and body, however, the decorative layer is 3-4mm thick as opposed to 1mm or less, which carries the design deeper into the tile adding the benefits of a through-body formulated tile. 

Sometimes double-loaded tiles are referred to as through-body tiles because the decorative layer runs deeper into the tile. These tiles are also called Double Pressed or Double Charged and should not be confused with Through Body, which has the decorative layer running through the entire body, not just the top 3-4mm.  Double Loaded Porcelain is very hard to find on the market in the US, as tariffs put a screeching halt to ceramic tile imports from China.  SHOP Architessa Double Loaded Porcelains Collections here.

Part C: Porcelain Innovation from the year 2000 +

Now that you know the difference in each product material classification, what possibly could be left?  Would you believe there are actually seven more classifications left?  Now comes the really fun part - porcelain innovation.  

Printing:  from Silk Screen to Rotocolor, to Digital Printing

A momentous & important time in tile history is the invention of digital printing in the 90s.  It took two decades to perfect, but porcelain tiles manufactured at large-scale factories are now all made using this process, creating patterns, shade, textures, and realistic images that are identical to natural materials or anything a tile designer could dream up. Of course, this will also make the historic tile events timeline, I previously mentioned, as it changed the industry as we know it today.  

Historically, manufacturers used silk screens to apply glazes. The resolution was low and each set of silkscreens produced only a single color pattern. The tile had to be rotated during installation or it was immediately obvious that every piece looked the same. The Roto-color process was a huge step forward in the 1990s and allowed for a pattern that wouldn’t be repeated for 20-30 tiles, however, the lack of graphic variation, natural shading, and general low-definition graphics left much to be desired design on the table.

Digital printing entered the market at the turn of the century and was not perfected until around 2010. Like the technology that changed the television industry, digital printing not only brought the most realistic image possible, it also meant that hybrid looks could now be introduced to the market along with added texture and dimension. Most tiles produced in large-scale factories utilize this technology, with a few exceptions such as deep bright colors (yellow, red, blue, green).  Much like the picture on your television screen, the graphics on tiles are made up of millions of small dots of color. The smaller the dots, the higher the definition.  

Digital printing is done without direct contact with the surface of the tile; the glaze is sprayed on. This removes the unprinted edges known as framing and the unglazed valleys that are often created with the Roto-color process. Digital printing technology also allows for the creation of low relief patterns, handmade effects, fabric looks, and mosaics. Trim shapes like Cove Base and Chair Rails can be made with the same process as the floor and wall tile, matching far better than with traditional methods. The digital process can also reproduce the look of wood, rustic natural stones, exotic marble, and slate as well as mix these looks together to create hybrid designs, without the cost and complexity of filling, honing, or double pressing.

While this concept is simple in theory, it has taken decades of painstaking work to bring the technology from the research and development laboratories to the production line. 

Innovation Post-Digital Printing

Since the year 2000, porcelain product categories have evolved at an unprecedented rate, making even more surfaces in your home and commercial buildings suitable for these lifestyle-geared tile products.  Before we dive into these next innovative categories, it’s notable to mention Sintered Stone, as it’s portrayed as a floating branch (or falling depending on who is looking at it). Sintered Stone products have been grouped as porcelain by some manufacturers that have positioned them as such, branding-wise. I personally classify Sintered Stone as a hybrid product, as it has similar manufacturing techniques and technical qualities.  Let’s take a closer look at the remaining categories.

CERAMIC TILE TYPES - Part C: Porcelain Innovation from the year 2000 +

What has it taken for the tile industry to become bigger, stronger, healthier, and smarter?  A whole lot of problem-solving, passionate, and dedicated people with Italian machinery is the oversimplified answer.  

Gauged Porcelain Tile  - Lighter weight tiles that measure≤1 meter (36”x36” or smaller) and range from 3-6.5mm.  This category evolved from the former category of “Thin Porcelain Tile” (TPT), but after sizes continued to grow, as well as thicknesses, the term GPT was coined to encompass a wider scope of products. Two classes of gauged tile products are defined

• wall applications =  3 to 4.9 mm in thickness
• floor applications = 5 to 6.5 mm in thickness.

Innovative projects with GPT include cladding on skyscrapers, or in large commercial lobbies or event spaces, where the party mementos of spilt red wine can’t outstay their welcome compared to natural stone. Turn up the volume DJ! 

Gauged Porcelain Tile Panels (Slabs)  - Tiles that measure>1 meter (greater than 36”x36”) and can span over 10.’  These porcelain slabs can be anywhere from 5’ to 15’ and are sold in basic patterns like Carrara and Thassos and exotic patterns like Zebrino and various Quartzites. These porcelain products were introduced to the US market after the year 2000 and were largely imported from Italy.  In layman's terms, this category is essentially very very large tile, sometimes thinner.  This category opened up the market to putting tile in places rarely acceptable before, such as; cladding buildings (clip systems), aircraft, yachts, recreational vehicles, furniture, and more.  Previously this category was only made up of thick natural stone, which is, of course, limited in application, design, and budget. Gauged porcelain is a category that has taken off very fast, partially due to the hard work of many industry stakeholders.  One of the most important stakeholders are the TCNA.  After thousands of hours of hard work put in by the TCNA, standards were born in the US in 2017.  The next year, in 2018, the first factory in the USA to produce Gauged Porcelain was completed in 2018. 

Low maintenance luxury has proved to be a largely appealing theme, as the availability of sizes and designs keeps growing in this category.  SHOP Architessa Porcelain Slab Collections here.

Pavers - Typical porcelain is between 8-12mm thick (approximately 1cm) and some it is suitable to put outside or on a covered patio (as determined by the manufacturer).  Porcelain pavers are twice as thick at 20mm (2cm) and are specifically created with higher slip-resistance & tensile strength to be installed outside without needing cover.  Before 2cm pavers, certain exterior installations are not suitable, such as over sand, gravel, driveways, or a pedestal system.  Pavers entering the market have provided more exterior options with size and look in porcelain, expanding the market for Pool decks, and interior to exterior seamless transitions (when matching 1cm material is available) and commercial properties - even boardwalks.  Using a pedestal system, you can actually create temporary floors for events or extra seating for Cafe visitors in the Summertime. This is most commonly done in Italy, but today, pavers are an economical hardscape option, and since they are digitally printed, the possibilities truly are endless.  SHOP Architessa 2CM Porcelain Pavers here.

Antimicrobial & Antibacterial - This category of porcelain has certainly been the most interesting one, given the past few years.  It’s arguably also the most difficult one to understand, rife with gray information and even different types of technology and manufacturing to confuse the masses.  These tiles have all been “branded” by each manufacturer, making it even more confusing for the end-user. Some of these tiles use nanotechnology.  Scientifically, nanotechnology is the field of applied science that manipulates matter at the nanometer (nm) scale. Nanoparticles are particles whose size is between 1 and 100 nm. Nanotechnology applications are highly beneficial for the development of new products as they provide tools that allow raw materials or materials to be preserved, improved, and/or acquire new properties. The benefits of these tiles are many and they typically offer up to 99.9% bacteria reduction, elimination of unpleasant odors, and permanent protection that doesn’t fade (as the technology is baked into the tile).  Some tiles have added titanium dioxide to create a photocatalytic activation, where the benefits are brought on via UV or artificial lighting.  Others are branded with the addition of silver-ions, or copper-nanoparticles, creating the extra benefits without the need for light.  When these tiles were first introduced, there was a bit of controversy in the industry.  At least one national hospital chain had even banned the use of these products in their facilities.  As of 2022, there is much less reason to worry because now we have ISO standards that can be tested in the TCNA lab.  The biggest limitation of this porcelain category is the limited number of design options, and of course, skepticism remains as tile is already a healthy choice.

“SMART” Tile - This category is my own personal classification.  In 2022 an Italian manufacturer recently announced the launch of integrated technology (baked into the tile) related to features such as lighting, temperature, audio-visual components, windows, and doors. Previously this category had integrated regular ceramics alongside companies outside the ceramic industry, using technology to create seamless designs in kitchen cooktops, and other sensor applications. Keep an eye on this category because it will be exciting to watch it grow from the luxury category to all consumers.     

Now that you have made it through the 3 parts, here is the full two-page chart showing all the Ceramic Tile Types.  If you would like to use this chart for training purposes or distribution please contact us for permission.

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Julie Taury

Julie Taury has thrived in the tile industry for two decades and held various positions ranging from retail sales to product development.  Her unique background in distribution, manufacturing, strategic sales, and the A&D industry has built an unparalleled skill set to navigate the unpredictable surprises of the tile industry. Currently, she is the Chief Innovation Officer at Architessa, and is a remote trailblazer, residing in New Zealand.