Hundreds of basement walls in northeastern Connecticut are crumbling, decades after they were built, according to press reports. As experts search for an explanation, attention is turning to the mineral "pyrrhotite," a mineral containing iron and sulfur that is known to damage concrete. Now, a Connecticut quarry operator whose stone is suspected of containing the problematic mineral has agreed to stop supplying the material to area batch plants — at least for now.

The New York Times reported on the basement problem on June 7 (see: "With Connecticut Foundations Crumbling, ‘Your Home Is Now Worthless’," by Kristin Hussey and Lisa W. Foderaro). "Across nearly 20 towns in northeastern Connecticut, a slow-motion disaster is unfolding, as local officials and homeowners wrestle with an extraordinary phenomenon," the paper reported. "Hundreds, possibly thousands, of home foundations that have been poured since the 1980s are cracking, with fissures so large you can slip a hand inside."

"The scope of the problem is so vast that state officials have begun an investigation, and they recently announced that the crumbling foundations had been traced to a quarry business and a related concrete maker, which have agreed to stop selling their products for residential use," the Times reported. "The stone aggregate used in the concrete mixture has high levels of pyrrhotite, an iron sulfide mineral that can react with oxygen and water to cause swelling and cracking. Over the past 30 years, the quarry has provided concrete for as many as 20,000 houses."

The Hartford Courant reported on the problem in May (see: "State: Foundations Are Failing At Least In Part Because Of Mineral Pyrrhotite," by Kathleen McWilliams). The Connecticut Attorney General's office and the state Department of Consumer Protection "reached an agreement with J.J. Mottes Co. of Stafford Springs to discontinue using or selling aggregate from Becker's Quarry in Willington for residential foundations until June 30, 2017," the paper reported. "The agreement also applies to Becker's Construction, another business in the family."

But John Patton, a spokesman for the Mottes company, said the basement failures still might prove to be a workmanship issue. "We continue to believe this is an issue of improper installation and not materials—findings which were proven in our only Connecticut court case involving a failed foundation," said Patton.

Pyrrhotite in the aggregate, however, is a plausible explanation. The mineral has been blamed in a similar rash of failures in the Canadian province of Quebec. In a 2013 article in the Journal of Civil Engineering and Architecture, Josée Duchesne and Benoît Fournier, engineering professors at Laval University in Quebec City, Canada, describe the mineral's mode of action (see: "Deterioration of Concrete by the Oxidation of Sulphide Minerals in the Aggregate"). "In the presence of water and oxygen," the professors write, "pyrrhotite oxidizes to form iron oxyhydroxides and sulphuric acid. The acid then reacts with the phases of the cement paste and provokes the formation of gypsum and ettringite. These minerals were observed by SEM-EDS (scanning electron microscope/energy dispersive x-ray spectrometer) and their precipitation causes a volume increase that creates expansion and cracking of the concrete."

Earlier reporting by NBC Connecticut also pointed the finger at pyrrhotite, and at the Mottes concrete company (see: "Crumbling Foundations," by George Colli). According to NBC, a Connecticut builder and a local building inspector reported widespread problems with basements poured by Mottes, and no similar cases in foundations placed by others. But Mottes has said that their company has detected the problematic mineral in other companies' basements, and that at least some of the problem foundations blamed on their concrete are the result of improper work practices by contractors, not the fault of the concrete. (For more of last year's coverage by NBC, see: "Crumbling Foundations: Homeowners Say Mottes Interview Raises More Questions," by George Colli and David Micnowicz.)