Porcelain Revealed - Tile and Stone by Villagio

Porcelain Revealed

There isn’t really any secret as to what a porcelain tile is: it’s a ceramic tile with an absorption rate of .5% or less. Incidentally, a .5% rating is also classified as “impervious”. This means impervious= porcelain, porcelain=impervious, impervious=< .5% absorption. However, all porcelains are not created equal. There are three general categories of porcelain tiles.

Natural porcelain tile
A.k.a. “technical porcelain”, “unglazed porcelain”, “unpolished porcelain”, or “through-body porcelain”. Natural porcelain is, as the name implies, porcelain that has not been glazed nor polished. These tiles are made of porcelain through and through. They can have surface treatments (soluble salts), have a different face and body (double loaded), or the face of the tile simply be a different color or texture than the body of the tile, yet it’s still classified as through-body “natural” porcelain. Most natural porcelain tiles have absorption ratings of less than .1%. Keep in mind that absorption has nothing to do with the facial surface being stain resistant. Unless the tile manufacturer has treated the porcelain to close up the surface (micro) porosity, you’ll need to seal natural porcelain tile before grouting.

Polished porcelain tile
Polished porcelains are natural porcelains with a polished surface. The polished surface isn’t a glaze, but actually comes from within the stone and it’s polished in a fashion similar to granite. It’s important to note that the polishing process on a porcelain tile actually opens up the pores of the tile. This means polished porcelain tiles must have a penetrating or impregnating sealer applied before grouting in order to increase resistance against staining and make them easier to keep clean.

Glazed porcelain tile
Many glazed porcelains are right at .5% absorption. However, if the bisque (clay body) of the tile is used as part of the visual design on the face of the tile the absorption should be under .1%. Glazed porcelains can be partially glazed, they can use glaze elements used in the manufacturing process or they can be completely glazed. There are even some glazes that can be polished!

Any type of porcelain tile has the following benefits when used residentially:

Design capabilities
When the manufacturer allows the bisque to show through the face of the tile, they can get a deeper, more realistic dimensions than ever before. To be honest, I would challenge any industry “expert” to correctly identify some porcelain tiles when compared to their natural stone counterparts once they’ve been properly installed.

Chip resistance
Through-body color porcelain tiles offer chip resistance in two ways. First, porcelain tiles have high mechanical strength and are extremely chip resistant. Second, if a through-body color porcelain tile does chip, the chip is the same color as the tile, so it doesn’t have to be replaced (unless the homeowner insists.)

Stain resistance
In the case of manufacturers who use glazes or use a process to close up the micro-porosity, the finished product will be extremely stain resistant, especially when compared to their natural stone counterparts.

Moisture resistance
If a tile has greater than .5% absorption it ISN’T porcelain. This means that all true porcelains are very dense and are ideally suited for use in high moisture settings. Whether you’re concerned about tile able to withstand freeze-thaw cycles or for use in swimming pools and spas, porcelain tile is a great choice.

Wear resistant
Natural porcelain is simply the hardest, most durable surface for high foot traffic installations. In floor areas in malls, grocery stores or banks, you just can’t beat the durability and beauty of natural porcelain.

Chemical resistant
All porcelain tiles are going to be much more resistant against citric acid, wine, mustard and other household chemicals than virtually any type of natural stone, including granite. This makes porcelain an ideal choice for kitchen counters and floors.

You can buy porcelain for less than natural stone; however, there are many porcelain tiles that will cost more than natural stone. However, keep in mind, that most porcelain tiles are technically superior overall to granite (the hardest of all natural stones) and many are virtually identical in appearance to natural stone.

Over the past 25 years porcelain tiles have a well-earned reputation as having the highest overall durability of all ceramic tiles or natural stones. The more you understand the features of this outstanding product, the more you can relay the benefits of owning porcelain to your customers.

Natural Stone vs. Ceramic Tile

Natural Characteristics
Understand that many natural stones may contain small naturally-occurring cracks (fissures), granite countertops may have some pitting and each stone has it’s own unique characteristics. Cracking and pitting are common complaints heard from consumers who were unaware of these characteristics when they selected natural stone. A common saying in the stone business: “If you want consistency and uniformity, then select porcelain tile”.

Installation Materials
The most common way to install ceramic (or porcelain) tiles is using the thin-set method with a 3/16″ or greater grout joint. Stones are commonly installed using a medium-bed or mud-bed installation with a grout joint 1/16″-3/16″. A thicker setting bed allows the installer to level the product and create a more level installation.

Installation Costs
Natural stone tiles and slabs are generally more expensive to install. This cost is primarily due to the overall difficulty of the installation combined with a tighter grout joint and buyers higher expectation of a flat floor.

If you own a large quantity of stone flooring, you will want to have it deep-cleaned on occasion. Also, most stones require a grout release before installation and a penetrating sealer after installation. A penetrating (or impregnating) sealer needs to be re-applied periodically per manufacturers instructions. Go to manufacturers websites for detailed maintenance instructions (i.e. crossville-ceramics.com, aquamix.com, miraclesealants.com, stonetechpro.com, etc.)

Vapor transmission
All stones breathe. This means they breathe up moisture from the slab and setting materials and they tend to breathe in moisture from external sources as well. This means all stones should be sealed using a penetrating sealer that allows vapor transmission, but inhibits staining. Vapor transmission also means that if you’re using a light stone over a large area, you may want to check the moisture in the slab (hydrostatic pressure) before installation begins. Keep in mind that as moisture passed from the slab to the stone, it’s possible to discolor some lighter stones from within the stone itself.

Frost resistance
Some slates are very frost resistant, which is why slate roofing is used in cold regions. However, other slates are simply not as condensed and will explode like a soda can in a freezer. Most stones are not suitable for outdoor installation in freeze-thaw conditions. Ceramic tiles with an absorption rating of over 3% are not generally suited for outdoor use as well. All porcelains (.5% absorption) have low absorption to be used outdoors, but the COF (Coefficient of Friction) must be suitable as well.

Wear resistance
Granites are the hardest of all natural stones, and there are some stone types that approach the hardness of granite. All polished stones scratch dull, yet some honed stones may be more difficult to clean than polished. A natural (through-body) porcelain tile can be up to 30% harder than granite.

Acid and Stain Resistance
Granites typically have superior resistance against staining. However, many common household products will stain or etch stone, yet most will have little or no effect on ceramic tile. For instance, an ice cold glass of water can etch ring on White Carrara marble. Vinegar, ketchup, mustard, fruit juice or wine will etch many stones. Again, look at sealant manufacturers websites for info on how to minimize (not eliminate) staining and etching.

Guide to Stone

Pocket Guide to Stone


Created from corals and shells that have settled on ocean floors and consolidated to form into calcite. Typically, there are visual fragments of corals, shells and other fossils in limestone. The density and hardness of limestone varies widely. The most durable limestone can withstand heavy airport terminal traffic (John Wayne Airport) while others aren’t adequate even for residential floors. Limestone is primarily available in subdued, earthy colors with a honed finish. It is not acid resistant.


Limestone deposits (calcite) that have been dissolved by groundwater. The characteristic holes in travertine are the result of the hot water and gases escaping during the formation process. Ideal for floors, walls, and splashes. The value of this stone is determined by: 1) the size and number of fill holes (density), 2) rare qualities or limited availability, 3) color consistency from tile to tile, 4) factory honing, polishing and/or filling processes. Colors are abundant in creams, chocolate brown, golden and red tones. It is not acid resistant.


The same geological makeup as travertine, however, onyx is formed in cool, cavernous conditions, similar to stalactites. Onyx is dense and will take a high polish. This multi-colored, translucent stone is most commonly available with a glossy finish. It is suitable for walls and extremely light duty (bathroom?) floors. It is not an acid resistant stone.


A travertine or limestone that has had heat, pressure and fluid activity applied and change in structure. This metamorphic transformation results in a denser stone with a myriad of colors that can be finished with a high gloss, hone or brushed. A polished finish is ideal for vertical installations or for horizontal installations where abrasion, stain and acid resistance are not a concern.


Stone that was formed by the cooling and crystallization of magma (molten rock). This extremely dense stone has a rather limited selection of colors. Granite can be finished a number of ways including flamed, hammered, a high polish. Among the most acid, stain, and wear resistant of all natural stones. Many granites are ideal for high traffic (commercial) floors and countertop installations.

Slate, Sandstone & Quartzite

As granite is broken down over time it forms smaller and smaller particles. These particles can be deposited into lakes, lagoons and oceans. Where these minerals have been deposited (along with heat, pressure and time) will determine the final stone. Finer particles can form shale. Shale, under heat and pressure, can form into slate. Beach sand can be consolidated to form into sandstone. Sandstone, under heat and pressure, can form into quartzite. With a natural cleft surface texture along with excellent acid, wear and stain resistance, many of these stones can be used indoors or outdoors in a variety of horizontal and vertical applications.

Performance-Ratings - Tile and Stone by Villagio

Performance Ratings

PEI ratings PEI rates abrasive resistance of the tile’s glaze on a scale of 0-5. This test is only for glazed tiles and does not apply to unglazed porcelain tile or other unglazed types of tile. Deep abrasion test for through body porcelain tile.

PEI ratings of glazed tile

Class 0. Suitable for walls only

Class 1. Recommended for wall use 
But may be used both on interior walls or bath floors without direct access to outdoor elements.

Class 2. Suitable for most residential floors 
May be used where abrasive foot traffic is minimal – such as bathrooms, bedrooms, dining rooms, living rooms, and sunrooms.

Class 3. Ideal for all residential floors
For floors subject to normal foot traffic and usage (including kitchens, outdoor entryways and hallways).

Class 4. Great for all residential and light-medium commercial 
Suitable for light to medium commercial applications. Will withstand moderate foot traffic in many commercial areas (commercial kitchens, hotel rooms, exhibition halls, etc).

Class 5. Great for all residential and most commercial 
Ideally suited for all residential and most commercial applications under normal foot traffic conditions (shopping centers, hotel foyers, walkways, and industrial applications). For very high traffic areas, consider and unglazed through-body color porcelain, which does not carry a PEI rating.

Mohs scale 
Frederick Mohs invented this geological scale of minerals to rate scratch resistance from 1-10. Think of Mohs as Method Of Hardness Scale. This test is not an industry standard but it’s a great comparison to show the difference in scratch resistance between tile and other hard flooring materials.

Coefficient of friction (COF) 
The coefficient of friction rates the slip resistance of a tile. ADA recommends a test rating of .6 (wet or dry) on floors and .8 for ramps. However, common sense must prevail. If you are told that a shiny surface tile has a .6 rating, stop and think if that tile really will be slip resistant.

Breaking strength 
The breaking strength test is a good indicator of the chip resistance of a tile because it tests the strength and density of the bisque. Using applicable ASTM test, ceramic floor tile typically has a breaking strength of 250 lbs. This can be less for poor quality tiles, higher with porcelain tiles (up to 400lbs).

What do you want your tile to do? 
Facial surface. A slip resistant surface may be more difficult to keep clean. A glossy surface may show dust and be slick. 
Body strength. Chip resistance, frost resistance, breaking strength, and water resistance. Make sure that the tile face and the tile body meets both performance and visual expectations.


Travertine is divided into four visual classifications. As with other natural stone products such as diamonds and precious stones, the value of travertine is based on the visual appeal, availability and rare qualities of the stone. As these are visual based categories, the durability or suitableness for a specific purpose are not part of this classification.

Commercial Quality 
Tiles with a commercial rating are divided into two distinct categories.

Class “A” is for appearance. The distinctive variation that occurs in an “A”. quality commercial stone may include a broad color range, a unique color range, usual mineral deposits or a moderate amount and size of fill. Class “A” commercial tiles will be of uniform thickness, squareness and size, but may have some variation in finish and fill color.

Class “B” is for dimension. Travertine tiles in this category may have variations in size or thickness, a considerable amount of fill or very large fill. These tiles are usually set with a 3/16” or larger grout joint.

Classic Quality A classic quality tile will be of a consistent size as to allow a grout joint of 1/8” or less. Classic tiles will have a moderate amount and size of fill. Classic tiles are sorted within a defined color range with minimal mineral deposits.

First Quality

First quality travertine tiles are sorted to have minimal fill and color variations within a defined range. First quality tiles have virtually no unusual mineral deposits and they are precision sized for minimal grout joints and ease of installation.

Premium Quality 
Premium quality travertine is so designated because of the unusually high density of the stone. This means that there are very few and very small holes. The face of a premium quality stone will be of discernible higher visual quality when placed next to other qualities of travertine