If you are confused about the coefficient of friction (COF), you’re not alone. This measurement that relates to traction and tile slipperiness evokes questions about the methods for measuring it, what a COF measurement actually means, how to compare COF values and what the COF requirements are. Thankfully, a new and better method for determining COF emerged in 2012, allowing project specifiers to more easily choose the right tile for the job. This new measurement, developed by the Tile Council of North America, is referred to as Dynamic Coefficient of Friction or DCOF, and now that many manufacturers have converted solely to DCOF in technical specifications, it’s important to understand what it actually means.
What’s the difference between the DCOF AcuTest and ASTM C1028?
The new testing method, the DCOF AcuTest determines dynamic coefficient of friction, in contrast to the ASTM C1028 test method which determines the static coefficient of friction, or SCOF. In the context of people walking on floors, static friction is the frictional resistance one pushes against when starting in motion. Dynamic friction on the other hand, is the frictional resistance one pushes against when already in motion. With both types of friction, a slip can occur when you push with more force than the surface can resist. The DCOF test relates better to slips occurring while a person is walking. Additionally, the new test method uses a slightly soapy solution (water with .05% Sodium Lauryl Sulfate, or SLS) that is more slippery than the de-ionized water used with ASTM C1028.
What is the required minimum DCOF value and how does it compare to SCOF values?
According to the new standard, ceramic tiles used in interior spaces that will be walked upon wet must have a minimum DCOF value of 0.42. Though it’s reasonable to expect that tile floors exceeding the SCOF minimum of 0.6 will also meet or exceed the new DCOF AcuTest criteria, it’s very important to understand there is no direct relationship between the two methods. The two methods measure different physical principles with different wetting solutions. To know if a floor definitely meets the minimum of 0.42 DCOF, it must be tested. Keep in mind that not all tiles with a DCOF of 0.42 or greater are necessarily suitable for all projects. Specifiers must also consider type of use, traffic, expected contaminants, expected maintenance, expected wear and manufacturer’s guidelines.
GIO Architectural Tile + Stone is committed to the simplification of tile and stone specifications. Our products are marked with both COF and DCOF ratings presented in a clear fashion so you can easily identify the technical characteristics you require.