Gloss and Grout: Standards for Ceramic Tile

Manufacturers will benefit from new standards developed under the aegis of the venerable ceramic whitewares committee.
Jack Maxwell

The evolution of ASTM as a standards-development organization tracks closely with the stunning advances in science and technology that have occurred since the organization’s founding in 1898.

In that time, ASTM has played an important role in helping a wide variety of industries thrive while navigating an ever-changing commercial and regulatory landscape. Newer committees, such as those working in fields like additive manufacturing and commercial spaceflight, get a lot of attention. But there are also long-standing legacy committees that have supported their respective industries for decades, ensuring that standards and specifications keep up with the latest technological advances.

One such committee is ceramic whitewares and related products (C21). Established in 1949, this group has been responsible for an impressive total of 61 standards over the years. Its members are still hard at work, as evidenced by two new standards nearing final approval. Following is a closer examination of these methods, as well as a celebration of the committee’s history and accomplishments.

An Ancient Material

C21 has been active for nearly three-quarters of a century, no small achievement. But the committee builds on a long history of ceramic use that began before humans had even completed their migrations around the globe.

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According to the American Ceramic Society (ACerS), the first ceramic artifact — a small statue of a woman found in what is now Czechia — dates to approximately 28,000 BC. Pottery fragments uncovered in East Asia are estimated to have been made circa 17,000-18,000 BC and represent the earliest examples of this type of ceramic ware.

There are too many other milestones to recount, but over the centuries, the art and science of ceramics have evolved to a remarkable degree. From the development of porcelain in China around the year 600 to the introduction of high-strength, quartz-enriched porcelain in the 1920s and high-temperature ceramic superconductors in the 1980s – to more recent work in the 3D printing of technical ceramics – this material continues to demonstrate its remarkable versatility and adaptability.

The average consumer may not realize it, but ceramics are a constant presence in daily life. Dinnerware, floor tiles, sinks, and toilets are all made from ceramic. Look up at the transformers on power lines and you’ll often see insulators made of ceramic whiteware. The spark plugs under the hood of your car are another example of ceramic used as an insulator.

On the industrial side, refractories — ceramics able to withstand operating conditions of 1,000° C or more — are used to line steel-making furnaces and cement kilns. Ceramic parts are crucial components of everything from filtration systems to abrasives used for polishing, grinding, and finishing processes.

Legacy Standards

The ceramic whitewares and related products committee has been helping the industry expand and evolve since it was formed. The committee’s work addresses key issues affecting both tile 
and whiteware, the two primary categories of ceramic products.

“It’s certainly been around for a while,” says Ryan Marino, standards development and research manager at the Tile Council of North America and a participant in all C21 subcommittees. “The committee manages a number of test methods and standards, many of which have been around since the early 1950s and ’60s.”

That word “methods” is worth noting. Fifty-three of the 61 standards developed by the committee over the years are test methods. Under the purview of the ceramic tile subcommittee (C21.06) alone, 18 test methods are currently active. They are designed to evaluate everything from thermal shock resistance to warpage and breaking strength to stain resistance.

Of the 25 standards managed by the subcommittee on methods for whitewares and environmental concerns (C21.03), 22 of the 25 standards are test methods. For those interested in something granular like the Knoop indentation hardness of ceramic whitewares, this is where to turn. The raw materials subcommittee (C21.04) is home to an additional 13 test methods that cover various analyses of whiteware clays as well as other ceramic ingredients like alumina, silica, and quartz powders.

Every one of these test methods addresses a potential performance or aesthetic issue. Tony Thornton, director of technical information at Micromeritics Instrument Corp. and a participant in no less than 13 committees, lists final strength, wear characteristics, and slippage (in the case of floor tiles) among such issues, as well as those relating to the manufacturing process like particle-size distribution and specific surface area. “And of course, having a common vernacular across the industry is critical for communication and understanding, and thus, standard terminology for ceramic whitewares and related products (C242) and standard terminology relating to surface imperfections on ceramics (F109) are near the top of the list,” he adds.

Porosity and Porcelain

Marino believes that one standard stands out for the vital importance of being able to determine water absorption values for ceramic tile and whitewares.

“I would say from my experience, probably the most influential test method is C373,” Marino says. [Test methods for determination of water absorption and associated properties by vacuum method for pressed ceramic tiles and glass tiles and boil method for extruded ceramic tiles and non-tile fired ceramic whitewear products.] “One of the main reasons it’s important is because the water absorption of a ceramic whiteware or ceramic tile determines whether or not it’s porcelain.”

Though the term “porcelain” is familiar to many people, those outside the ceramics industry might not understand how exactly this type of ware differs from other types. It all comes down to porosity: porcelain is almost completely impervious to absorption of liquids.

“The lower the available porosity, the more sealed that whiteware or tile might be,” Marino says. “When you want to reduce stains, or prevent stains from occurring, you want the surface to not be porous. Otherwise, it may pull in those liquids, which can then lead to staining or moisture retention. Porcelain is a term that’s used throughout both industries and brings with it a certain idea of quality. If something’s supposed to be porcelain, C373 is the method that you would use.”

Low-Angle Light Defects

One of the in-progress standards referenced earlier is intended to address the issue of inconsistent surface reflectivity in ceramic tile – and the fact that the way evaluation of this attribute is typically done by the manufacturer does not always catch this type of defect.

There are many standards for ensuring the quality of tile.

Marino points out that, in the factory, tile that is being examined as part of the quality-control process is generally viewed from a high angle, looking almost straight down. However, there is currently no standardized methodology that spells out how to check for inconsistency from other perspectives, nor are there any machines sensitive enough to detect such minute variations.

This is a problem for manufacturers because the angles from which consumers might see the tile in their homes or workplaces can vary, revealing cosmetic flaws not picked up during the factory 
QC check.

“Let’s say you’re walking into your house and the sun is on the back side shining through your glass doors,” Marino says. “You may see if a tile is subject to low-angle light defect. You may see a difference in gloss from tile to tile at that distance, because you’re looking at that low angle.”

The new standard test method for determining low angle light defects (WK76972) provides details on how to construct a light box in which to place tiles for viewing, and additional instructions on where to stand and how to look at the samples and compare tile to tile to look for variations.

This work item was balloted for the first time at the subcommittee level in July 2023. It moved to the main committee ballot in December.

Tile Grout Retention

The other new standard developed by the C21.06 subcommittee concerns the grout-retention properties of tile. While this issue may sound like it relates to how well grout performs its task of helping to secure tile to a substrate like a floor or wall, Marino clarifies that it’s really about a more basic problem: grout discoloring or otherwise impacting the tile’s surface.

“Ceramic tile has some porosity to it,” he says. “Typically, when you’re grouting over tile, or when you’re trying to fill in grout joints, you’re spreading that grout and it kind of hits all over the tile even though your main point is to hit this sixteenth-inch to quarter-inch-wide joint in between tiles. In some cases, the pigment from the grout or the grout itself might end up affecting the look of the tile.”

Marino cites an example where a design calls for a bold look featuring white tile and black grout. If the tile is especially porous, it can absorb some of the black pigment, or even the grout itself, leading to a result that, in his words, “is not terribly pleasing to consumers who bought, paid for, and had tile and grout installed in their home or business.”

The new test method will give a tile manufacturer the ability to detect whether its products could be susceptible to this kind of staining before they’re installed. It’s fairly simple, spelling out a procedure wherein one side of a tile is masked off, the other is left exposed, and the grout is spread over the exposed side and allowed to dry, per the grout manufacturer’s instructions.

“Then you try and clean the grout off, take the tape off the masked side, and compare the grouted and ungrouted sides,” says Marino. This process will reveal if there is an issue. “There are products out there that help release grout from the surface, so if you’re going to have a problem with grout retention, you may want to consider using a grout-release compound that will help protect the tile while you’re grouting.”

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The new standard practice for grout retention properties of tile (WK83661) went through two rounds of balloting at the subcommittee level last year. It also went to the full committee in December.

Manufacturer-Driven Standards

An intriguing aspect of these new ceramic tile and whiteware standards is the fact that they were initiated by a manufacturer. 

“One of the interesting things from my perspective is that this is an issue for manufacturers, and it’s manufacturers that are leading the way in coming up with a solution,” says Marino. “They’re not trying to build standards to make their products look better. In fact, they’re trying to build standards to help make their product better for consumers,” he says.

This cooperative approach contrasts with other scenarios where an individual company might work quietly to solve a problem and then keep its proprietary solution close to the vest. It speaks 
to the strong consensus-building culture fostered by ASTM.

“One of the things I like about ASTM and about the ceramic tile industry overall is that it’s very collaborative,” Marino says. “We don’t have trade secrets or things people are trying to keep to themselves for competitive advantage. Every day I see manufacturers take off their company hat and put on their industry hat and set their company aside for the betterment of the industry. It’s good to be a part of something like that.”

Dick Eppler knows something about ASTM culture. He’s been an active participant for nearly 60 years, including two stints as chairman and as a member of numerous committees. C21 has been his primary focus, and he continues to chair the subcommittee on editorial and terminology.

“From my personal viewpoint, ASTM jurisprudence is so much better than the other options out there,” Eppler says. “There’s a rule in ASTM that after a committee has considered a particular objection, you can’t bring it up again. In other words, the committee does not have to keep considering the same thing endlessly.”

This structure, designed to create consensus, has facilitated the collegial atmosphere found within C21 and enabled the committee to work efficiently on behalf of ceramic whiteware and 
tile manufacturers.

“As with most committees, C21 was formed to answer an industry need for standardization, in terms of specifications and the test methods used to verify these specifications,” notes Thornton. “Such standardization improves manufacturability and usage in final applications.” It seems that this long-standing committee continues to meet that need. ■

Jack Maxwell is a freelance writer based in Westmont, N.J.

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