We are currently reviewing our workspace for potential ESD issues, and our facilities manager opined that 'bare concrete' is the best "anti-static" flooring there is. He offered no source for his information, and I didn't find this question even asked on your [otherwise very informative] website.

So: What do you think of the ESD properties of bare concrete?

Believe it or not this is one of those questions that everyone should ask and, as you noted, I should have proactively answered. Bare concrete would certainly provide an inexpensive floor.

I assume you are asking about bare unsealed concrete that is allowed to breathe.

First, ANSI/ESD S 20-20 recommends a system resistance of less than 35 megohms from the person through the controlled footwear floor and on to ground. As resistance increases, charge dissipation performance decreases. The fact that something exhibits antistatic tendencies does not mean that it will also discharge a human being properly. Discharge or dissipation is directly related to conductivity and not to antistatic properties. Calling a floor “antistatic” only means that floor will not contribute to tribo-elctrification. It does not mean that it will also act as a ground.

While bare concrete often exhibits antistatic (and dissipative or conductive) tendencies, these antistatic characteristics are not inherent in concrete, as they are in a carbon filled-material. The problem with designating concrete as “the ESD floor” is the uncertainty of its resistive properties—which are subject numerous variables, including the degree of moisture permeation, changing environmental and geological conditions, weather, environmental humidity and freeze/thaws. Since its antistatic tendencies are drawn directly from the concrete floor’s moisture levels, concrete has— at best - unpredictable conductivity.

I have measured the conductivity of some concrete that I found to be too conductive only to see that same concrete measure almost insulative at another time in same year. This broad performance differential would be a hard sell to a knowledgeable auditor (or customer) as part of any ISO certification process. Bare concrete with high conductivity usually means a damp and often dusty building. On a similar note, I was once asked to show an engineer in Florida why he should use static dissipative table covering instead of old back issues of the Miami Herald. The Herald actually performed marginally better than the special table covering – on that beautiful but humid day. Fortunately, he didn’t have a dilemma over justifying special table covering since damp news print, while antistatic, is also unfit for a clean environment because it is corrosive.