An installed electrostatic discharge (ESD) floor can produce different resistance readings from a laboratory sample because the flooring assembly, connection to ground and test conditions may differ. Comparing the results requires checking how each measurement was taken, including the test voltage, curing, humidity and recent cleaning.
STM7.1-2020 is an ESD Association standard test method (STM) approved by the American National Standards Institute (ANSI). ASTM International publishes the F150 test method.
Two different measurements
Under STM7.1-2020, resistance to a groundable point on a qualification sample is distinct from resistance to ground on an installed area. The standard says those readings may differ, especially for floor finishes.
The installed floor is a system of interacting components
What counts as the flooring system
STM7.1-2020 defines a flooring system as the full combination of components used to control electrostatic charge, such as the surface material, the adhesive, the grounding mechanism, the substrate, and any other material in the system required to carry a static charge to ground. The foreword to the standard notes that the test is applied to that system of materials and that the interactions among those materials can affect the overall resistance measured.
A conductive tile in a dissipative system
A conductive tile can end up in a dissipative system. Informative Annex B of STM7.1-2020 gives the example of a glue-down tile with a resistance of less than 1.0 × 10⁶ ohms, characterized as conductive, installed with an adhesive with a resistance of 1.0 × 10⁶ ohms or more. The result is a system with a resistance to ground of 1.0 × 10⁶ ohms or more, which would be characterized as dissipative rather than conductive although the tile on its own is conductive. Any faulty element of the system, such as a regular insulative adhesive, would cause the system to fail.
Substrate moisture and minerals
Informative Annex B of STM7.1-2020 notes that adhesives can be affected by the moisture or mineral content of the substrate on which they are applied. Where the adhesive, rather than the tile, is the main controlling element of the system, a change in substrate moisture or mineral content can change the adhesive resistance and with it the resistance of the flooring system.
Test voltage
One material, two readings
The foreword to STM7.1-2020 describes materials that measure 1.0 × 10⁶ ohms or more at a test voltage of 10 volts but less than 1.0 × 10⁶ ohms at a test voltage of 100 volts. A difference between a report at one voltage and a reading at another can be a voltage effect rather than a change in the floor.
Why 100 volts can read lower
Informative Annex C of STM7.1-2020 notes that, depending on the material being tested, 100 volts or higher may cause a breakdown in the material, creating a less resistant path that may not be indicative of the resistance of the flooring system. The annex adds that this may give a misleading characterization of the flooring system’s triboelectric charge and discharge capabilities. A lower reading at the higher voltage is therefore not necessarily a sign of better electrostatic performance. A lower reading at 100 volts does not, by itself, establish that breakdown occurred.
Cure state
In the acceptance procedure of STM7.1-2020, testing a newly installed flooring system before finishes, coatings, or adhesives are fully cured yields resistance measurements that may differ from those measured after the materials are fully cured.
Humidity and moisture
Laboratory conditioning versus installed-floor conditions
STM7.1-2020 qualification uses two defined conditioning environments; installed acceptance testing uses ambient humidity.
| Qualification environment | Relative humidity | Temperature | Preconditioning |
|---|---|---|---|
| Low humidity | 12% ± 3% | 23°C ± 3°C | At least 72 hours |
| Moderate humidity | 50% ± 5% | 23°C ± 3°C | At least 72 hours |
Readings can vary with ambient humidity
Clause 8.3.1 of ASTM F150-25, the ASTM test method for the electrical resistance of conductive and static dissipative resilient flooring, notes that areas with lower ambient relative humidity could have resistance readings that vary from readings at higher ambient relative humidity. The clause says only that readings could vary; it gives no direction or amount.
Cleaning moisture and equilibration time
Informative Annex B of ANSI/ESD STM97.1-2025, the test method for footwear and flooring system resistance measured in combination with a person, notes that moisture or water introduced from the environment or from cleaning may lead to misleading resistance values if testing is done immediately after cleaning. Some materials are hygroscopic (moisture-absorbing) by nature and may exhibit widely varying resistance results at different relative humidity levels or with moisture introduced from cleaning. The time needed to allow the surface to equilibrate (reach moisture balance with its surroundings) may be longer than 72 hours. The annex is informative rather than part of the test method, and it fixes no universal equilibration time. It also does not change the preconditioning of at least 72 hours that STM7.1-2020 specifies for qualification.
Comparing two test reports
Before interpreting a difference as a change in flooring performance, compare the measurement type, flooring components, test voltage, cure state, temperature and humidity recorded for each test. Check whether recent cleaning or different conditioning periods could also have affected the results.
Frequently Asked Questions
The ground path, system components, test voltage, cure state, and humidity can differ. STM7.1-2020 specifically notes that resistance to a groundable point on a qualification sample may differ from resistance to ground on an installed area, especially for floor finishes.
No. Informative Annex B of STM7.1-2020 describes a conductive glue-down tile below 10⁶ ohms installed with an adhesive at or above 10⁶ ohms, producing a system with resistance to ground at or above 10⁶ ohms and characterized as dissipative. The complete assembly matters, including the adhesive and grounding components.
Not necessarily. Informative Annex C of STM7.1-2020 says that, depending on the material, 100 V or higher may cause breakdown and create a less resistant path that misrepresents the flooring system’s resistance and triboelectric charge and discharge capabilities.
No universal equilibration time is established by the informative humidity discussion in Annex B of STM97.1-2025. Some hygroscopic materials may need longer than 72 hours, and moisture from cleaning can make immediate resistance readings misleading. This informative discussion does not replace STM7.1-2020 qualification’s specified preconditioning of at least 72 hours in each defined environment.