Conductive adhesive forms a ground plane unifying ESD tiles. Learn how conductive adhesive works and why the adhesive must be more conductive than the floor.
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What is Conductive Adhesive?
Conductive adhesive is an electrically conductive glue used to create a bond between a subfloor—such as concrete, raised access panels, or old vinyl tile—and a static-control floor.
In the manufacturing process, carbon or graphite particles are mixed into the liquid adhesive. These suspended particles touch one another, creating an electrically conductive matrix.
Installed over the subfloor, the adhesive forms a “sticky” plane with conductive properties. Copper strips attached to the adhesive connect the adhesive and the tiles to ground, unifying the electrical potential of the flooring system—i.e., the adhesive, all flooring tiles, people and machinery on its surface.
What Does Conductive Adhesive Do?
Static-control flooring works as a system, creating an electrical circuit that directs charges to ground. An integral part of the system, conductive adhesive performs two important tasks:
- The glue creates a mechanical bond: like regular glue, conductive adhesive holds ESD-tiles or sheet flooring in place;
- The adhesive forms a ground plane under the static-control floor tiles. This ground plane enables electrical interconnectivity, creating a path to ground across the entire floor.
Why Do You Need Conductive Adhesive?
With an effective static-control flooring system, static flows from the human foot to the flooring surface; through the thickness of the floor; across the ground plane formed by the conductive adhesive; to the copper strip; and from the copper strip to electrical ground.
Without a conductive ground plane, static electricity has nowhere to go. Rather than flowing downward to ground, charges remain on the surface of the floor. If the room houses energized equipment—a mainframe computer, for instance—contact from the metal chassis will inadvertently ground the floor, making the surface of the floor part of an unintended electrical pathway. Under these conditions, if the floor is too conductive, a person reaching into the computer could become part of a dangerous electrical circuit. That’s why the floor should always be the most resistive—or least conductive—component in an ESD flooring system.
To Work, Does the Adhesive Have to Be Conductive?
Yes. Grounding is not achieved through tile-to-tile contact, no matter how conductive the flooring material. Grounding an ESD floor requires a conductive underlayment or ground plane. Conductive elements in the floor, in combination with the conductive underlayment, draw charges downward, through the thickness of the tile, across the ground plane, to ground.
System resistance is always equal to or greater than the most resistant—again, least conductive—component in the chain. To direct static electricity downward to ground, as intended, the adhesive should be the most conductive element in the flooring system.
Like any electrical current, static electricity seeks the fastest pathway to ground. That pathway should be below—never across—the surface of the floor.
If the adhesive is not conductive, or the flooring material is more conductive than the adhesive, electrical charges will bypass the adhesive, preferring the easier route, across the top of the floor—to the chassis of energized equipment, for example, or grounded electrical consoles, or the frame of a large UPS (uninterruptible power supply) in a data center.
That’s why, for safety reasons, grounding documents like FAA-019f and Motorola R56 require the use of static-dissipative–rather than conductive—flooring near energized equipment in human-occupied work environments, such as flight control towers or mission-critical call centers.
Can the Adhesive Change the Resistance of Static-control Flooring Materials?
No. Flooring materials obtain their electrical properties in the manufacturing process—determined in part by the volume and distribution of conductive particles—and cannot be changed.
Surface Resistance (RTT) and System Resistance (RTG)
The electrical resistance—measured from point-to-point, across the surface of flooring materials or tiles (RTT)—is different from resistance-to-ground (RTG), or system resistance*—which tests the resistance of the entire flooring system, including the person and the footwear the person is wearing.
* System resistance tests the rate at which static charges flow from the person (holding a probe), though his or her footwear, to the surface of the flooring material, through its thickness, across the conductive adhesive or ground plane, to the copper strip/ground.
The resistance across the surface of some flooring materials can read differently—higher or lower—than readings for the entire flooring system. That’s because each component in the chain has some degree of electrical resistance, and the system is the sum of its parts. The only way to determine how a flooring material will work after it’s installed is to test both point to point (RTT) and resistance to ground (RTG).
Fact: system resistance is always equal to or greater than the most resistant individual component in the chain.
Adhesives with higher electrical resistance than the flooring material will slow the rate of charge dissipation to ground. In effect, a charge could speed from the surface of a conductive floor, through the thickness of the flooring material; once the current reaches the adhesive, the higher resistance will slow its progress, causing it to reach ground at a slower rate than would have been predicted from material resistance alone.
It’s like the difference between walking on land and walking through water. The water resists, or hinders, your ability to move, slowing you down.
The adhesive did not in any way alter the resistance (or conductivity) of the flooring material. It did, however, raise the overall system resistance—making it appear as if the floor were more resistant (less conductive) than it actually is. To confirm that a flooring material meets electrical specs for the specific application, test surface and system resistance—then compare the results, to be sure the numbers jibe.
Why does it matter if RTT and RTG tests show different results?
To reach ground, a static charge has to move from the surface of a flooring material through its thickness to the adhesive, then across the adhesive to the ground connection. Assuming the floor has the highest resistance in the system, the conductive adhesive will pull electrical currents downward, through the adhesive.
Fact: electrical current, including static, always seeks its fastest path to ground.
If the adhesive is more resistant than the flooring material—under certain circumstances involving energized equipment—rather than take the slower, more resistant path downward, through the adhesive, current could move across the surface of the flooring material, posing a potential safety hazard to people on the floor. This is basic physics. That’s why it’s critical to test the floor point-to-point (RTT) and resistance to ground (RTG), and do due diligence to be sure that the adhesive is more conductive than the flooring material.
Organizations like the FAA require testing individual components of the flooring system to determine if the surface of the floor might be more conductive than the adhesive securing it. They perform these tests because if the system resistance is higher than the surface resistance they know they have a potential safety hazard.
Test resistance of individual tiles before installation.
Test system resistance post installation, and once a year through the life of the floor.
Humidity Can Change the Conductivity of Adhesive
The conductive adhesive is the only part of a permanent static-control flooring system that is truly environment-sensitive. When concrete humidity is high, the adhesive can absorb moisture, in which case the electrical resistance of the conductive additives decreases. When humidity is low, the adhesive dries and becomes less conductive.
If the resistance of the flooring material is too high or too low, environmental conditions that change the conductivity of the adhesive will affect the performance of the floor, exposing electronics to unwanted static discharge events, or potentially creating an overly conductive environment with unsafe low resistance.
Flooring materials with high resistance (above 1.0 x 10E8)
If the resistance of the flooring material is too high, as the RH drops and the adhesive becomes less conductive, the system resistance could increase too much to dissipate static, in which case the floor would perform like a regular, non-ESD surface.
Flooring materials with low resistance (below 1.0 x 10E5)
Adhesives can become more conductive due to high RH or changing dew points from contact with bare concrete. If the flooring material is too conductive, as the dew point rises and the adhesive absorbs moisture-increasing its conductivity-the overall system resistance could drop to unacceptable levels.
The same can happen in reverse: if the flooring material is too conductive, as RH drops and the adhesive loses conductivity, becoming less conductive than the flooring material, a situation like the one described above could arise, with current bypassing the underlayment, cutting across the flooring surface instead.
Both of these problems can be pre-empted by using flooring materials that are not too conductive.
To avoid risks, test resistance before and post installation
As long as both the tiles and flooring system measure in the proper range, ideally between 1 x 10E6 and 1 x 10E8, changes in humidity should have a negligible effect on the electrical performance or safety of the floor. To avoid unnecessary risks, the resistance of individual tiles should be tested before installation, and system resistance tested post-installation, then at least once a year through the life of the floor.
Will conductive adhesive change the conductivity of regular, non-ESD floor tiles?
No. Electrical resistance is inherent and cannot change. Certain environmental conditions, such as dirt and debris, can render an ESD floor less effectively conductive: dirt and debris prevent contact with shoe soles so that the floor cannot properly dissipate static charges. But environmental conditions, while potentially affecting performance, don’t change the conductivity of the material.
Regular, non-ESD floors are insulative. With no embedded conductive fibers or filaments, the flooring material has no way to promote the flow of electricity, so currents-or static charges-remain on its surface. The lack of conductive elements also prevents electrical contact, or bonding, with the conductive adhesive. In effect, the conductive adhesive might as well be regular glue.
Can conductive adhesive be used on a subfloor with a high vapor content?
Conductive adhesives break down and liquefy when left in contact with high RH concrete. Concrete is a naturally alkaline material. In conjunction with high humidity, the high pH of concrete eats conductive adhesives in the same way wax strippers break down wax. To use conductive adhesive, you need a topical vapor barrier or a roll-out vapor barrier like Versashield.
Are there ways other than conductive adhesive to ground an ESD floor?
Yes, an ESD floor could be installed over raised access flooring panels made of bare metal. Most ESD flooring materials would be grounded upon contact with the bare metal panels. Alternatively, a glue-free, floating floor, such as ShadowFX SD carpet tile, can be installed over a proprietary conductive underlayment like Staticworx GroundBridge™. The GroundBridge underlayment, like bare metal access panels, would act as the electrical unifier between tiles.
Do the same rules, about resistance relative to the floor, apply to other underlayments?
Yes, what’s under the surface should be more conductive than what’s on top. Direct the charge “Down and Out.”
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With Staticworx ESD flooring, you never have to choose between performance and aesthetics. Our beautiful, high quality ESD carpet tile, vinyl, EC rubber tile and sheet goods, and ESD epoxy floors are as beautiful as they are functional.