YMSW Journal
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Testing Stone

Because stone is an organic material continuously influenced by elemental and human factors, designers and installers need to understand how different stones respond, both aesthetically and functionally, to different influences and over time. Testing stone against the demands of the finished project can be extremely helpful in selecting appropriate stones and finishes, preventing problems, and determining how a particular stone may perform after a given number of years. Armed with this knowledge, design and construction teams can make informed decisions and set realistic expectations.

“In essence, testing allows us to look into the future and predict how a given stone and finish is likely to perform in a specific design and environment,” explains Nicole Gelpi, YMSW Owner and Director of Marketing. “Testing provides a holistic picture of a stone which helps the project team collaborate on the best product and installation solutions.”

Advancing technology has created lab-based testing scenarios that can address a number of influential factors and be targeted specifically to the needs of an individual project, for example:

Freeze/Thaw Conditions: For projects located in environments with significant swings in temperature, testing looks at permeability and moisture absorption. When water freezes, it expands, which can lead to cracks and rupturing of material. During the thaw cycle, evaporation can cause minerals to crystallize, creating efflorescence deposits or pits on the surface of the stone. To test the effects of freeze/thaw conditions, the stone is immersed in water until it absorbs all the moisture it can and then frozen and thawed repeatedly.  The integrity of the stone is based on X number of cycles along the continuum of testing.

Compressive Strength: Testing of compressive strength looks at the load capacity and can indicate how thick the stone needs to be to achieve the required strength. This is more likely to be an issue with softer stones, like sandstone. To test for compressive strength, increasing amounts of weight are put on top of the stone until it fails. The integrity of the stone is based on the average test results over multiple iterations using X number of sample sizes. Compressive strength testing, using scenario specific apparatus, can also determine a stone’s response to persistent weather conditions such as hail, wind, and salt spray.

Flexural Strength: The goal of flexural strength testing is to determine a stone’s ability to resist a load put on its surface asymmetrically, for example, a cantilevered stone with a load on the unsupported end. To test for flexural strength, the lab will cantilever a test section and then increase the unsupported load until it snaps, indicating the “bending moment.” The results of flexural strength testing can be particularly useful in indicating the best installation method for a given stone; for example, a sand set application with a pebble integrated in the subgrade can increase the flexural strength.

Chemical Resistance: When sulfurous, sulfuric, and nitric acids in polluted air react with the calcite in carbonate-based stones such as marble, travertine, and limestone, the calcite can dissolve resulting in roughened surfaces, removal of material, and loss of carved details. Testing involves exposing stone to chemical solutions resembling the acidity of the acid rain found in the relevant polluted environment.  The integrity of the stone is based on X number of cycles along the continuum of testing.

Coefficient of Friction: Friction testing is used to determine slip resistance. A “slipping machine” is used to force of variety of replicated heels, i.e. barefoot, rubber soled shoes, high heels, etc., onto a stone at a given load to slide it sideways. Testing determines the coefficient of friction by showing the pounds of lateral thrust required to move the heel on the surface. Building codes require that exterior surfaces have a coefficient of friction of X, depending on use. Different finishes provide varying degrees slip resistance; testing multiple finishes allows us to help designers and builders achieve both aesthetic and functional requirements.

Testing stone is a proactive measure that allows a project team to evaluate different stones across multiple factors. Going beyond design and environment, test data can also influence decisions around budget and upkeep. For example, if test data shows that two different stones meet the strength and aesthetic requirements of a project, the team can confidently go with the less expensive option. In another scenario, if the owner has indicated they want a low maintenance solution, test data can help us to recommend stones and finishes that minimize maintenance.

On a final note, while testing can provide useful insight into a stone’s viability, it is not a guarantee of performance. “The reality is that installation trumps testing,” explains John Williams, YMSW Owner and President. “Testing results are based on simulated conditions that should inform the installation process specific to method, set material, drainage, air circulation, etc., but ultimately, the quality of the installation determines the performance of the stone.”

For a list of all relevant tests performed on dimensional stone, reference the standard guide published by ASTM International (formerly known as the American Society for Testing and Materials).


Topic: Insights
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Great Expectations

Intrinsic variability is what makes natural stone both beautiful and challenging. Limestones in particular can feature an array of desirable characteristics, such as veining, fossils, and color movement, yet these elements can vary in frequency, size and range within the same quarried block. Left uncommunicated and unresolved, the stone can fail to meet client expectations, alter the design intent, and potentially increase costs and time to completion if the client requires the stone be replaced.

“It’s critical to the success of a project to proactively manage expectations and collaborate on solutions that optimize the stone and meet the requirements of the project,” said John Williams, YMSW co-owner and president. “We look at the extent of the combined variables to drive the process – the richer the variables, the more involved the review points need to be.”

An excellent example of a more involved process is the recently completed Via6. Designed by GGLO and built by Lease Crutcher Lewis, Via6 is currently Seattle’s largest retail and residential complex. Covering half a city block, the design intent for Via6 was to communicate the high-end quality of the building by using high-quality materials with a handcrafted, artisan aesthetic. As a result, a granite and three unique limestones in various sizes and utilizing multiple, hand-textured finishes cover the 15- to 19-foot vertical height of the Via6 base.*

Limestones can be complex to define within design parameters, particularly on larger pieces, because of the mutable nature of its organic characteristics. It’s important to understand the nature of the stone and then create a set of standards, or a range, that meets the design intent and against which we can fabricate the required pieces. For example, how many fossils are too many, how big is too big; what is the size and visual quality of veining; what is the range of color?  Defining the range too narrowly can result in more waste and higher costs; defining it too broadly can result in an uneven aesthetic.

“YMSW was incredibly helpful in educating our team about what stone is all about and to appreciate its natural, organic qualities,” said Steve Nordlund AIA, the project’s lead architect for GGLO. “We went through an extensive review and collaboration process that started with 6- and 12-inch square samples we could mull over in the conference room and ended with a trip to China to see full scale mock-ups.”

The initial smaller samples can help designers choose a color and texture palette, but the proof is in the full scale mock-ups YMSW provides because they most accurately show the range of color and likely occurrence of fossils and veining. As the final approval point, mock-ups also provide a reference point throughout production.

“On all of our projects, half of the mock-up goes to the client for review and approval, and half stays in China with the fabricator as a benchmark,” explained Williams. “But because of the scope of the Via6 project and the numerous variables in play, there was no substitute for being at the factory where we could collaborate in real time with our fabrication vendor and the Via6 developer, architect, builder, and stone installer.”

“It was important to have everyone there so that we could talk about the design as well as the construction and installation of the stone,” concurred Nordlund. “The full scale mock-ups allowed us to set parameters around the color range we wanted to achieve across the Ginseng Cream Limestone, and made clear the amount of veins in the Ink Jade Limestone – which enabled us to dictate where the pieces with more veining were placed in the project.”

“The ultimate outcome of the mock-ups is that we come to an assembled whole that looks correct,” explained Williams. “By correct, I mean that there isn’t any element that’s drawing undo attention to itself; the overall effect is a blend. This allows us to be more efficient throughout production by shifting the focus from an in-depth analysis of every piece, to the overall intent of the assembly.”

“YMSW was extremely helpful and knowledgeable,” said Nordlund. “Their process allowed the project to be completed as planned.”

*For more information about the scope and complexity of the project, go to our Via6 featured project page, "A Contemporary Jewel Box."


Topic: Insights