Hundreds of Connecticut homeowners have complained that the concrete foundations holding up their houses are crumbling, and state authorities blame the mineral content of a stone aggregate mined in an eastern Connecticut quarry.

According to an NBC Connecticut report, significant amounts of an iron-sulfide mineral called pyrrhotite in rock aggregate is causing foundations to crumble. The station’s report, which shows someone easily flicking away the surface of a concrete wall with the tip of a screw, says that thousands of residential foundations may be affected.

The problem was first reported last July. Most recently, Becker’s Quarry in Willington, Conn., and J.J. Mottes Company in neighboring Stafford Springs, a ready-mix concrete supplier, have signed an agreement with the state to stop selling materials that contain aggregate from Becker’s Quarry until June 2017.

The station said it has been told by construction experts the foundations can’t be repaired and must be replaced, which could cost $150,000 or more per home.

The state’s Department of Consumer Protection has heard from 220 homeowners, but the station says that thousands of homes in the eastern part of the state could be affected.

In a written statement, Connecticut Attorney General George Jepsen said, “Although that investigation will continue into the fall, we believe there is now sufficient evidence to conclude that significant levels of the mineral pyrrhotite in stone aggregate used in the production of concrete is a substantial contributing factor to the crumbling foundations experienced by some homeowners in eastern Connecticut… Further efforts are necessary to understand the full range of contributing factors and the manner that all factors interact to produce concrete deterioration.”

The problem appears to be limited to residential foundations, and the aggregate from Becker’s quarry can still be used in commercial applications, the station said.

Firms say that installation is the problem

A spokesman for the Joseph J. Mottes Company, which has leased its property and equipment to a another Connecticut firm for the 2016 building season, said that the failures were an “installation issue.”

“We strongly believe that the current situation involving residential foundations in eastern Connecticut is an installation issue, and we support an unbiased and comprehensive investigation of these foundation issues — including how the materials were placed and installed, in addition to remedial actions — so that homeowners can get the answers they deserve and meaningful help with solutions,” Mottes spokesman John Patton told the Hartford Courant.

Patton didn’t elaborate on what kind of installation errors might have contributed to the problem.

Neither the American Society of Concrete Contractors nor the American Concrete Institute (ACI) could produce a technical expert to discuss the potential risks of using aggregate with high pyrrhotite content, or whether the problem has been reported in other parts of the country.

A search of ACI’s online archives for “pyrrhotite” turned up just two entries. One of them is an article dating from 1959, which said in part, “In the Oslo region of Norway, alum shales containing small amounts of the unstable iron sulfide, pyrrhotite, produce an unusual form of sulfate attack upon concrete placed in or near these deposits, and cause deterioration if they are used as concrete aggregate.”

The rest of the article is behind a pay wall.

Problems in Quebec reported in 2002

Pyrrhotite-laced aggregate apparently hasn’t attracted much attention in the U.S., but a well-documented case in Quebec near Trois-Rivieres has involved more than a thousand homes, according to the website Pyrite Problem.

Reports that houses were showing concrete problems related to the pyrrhotite content of aggregate began trickling in back in 2002. Later, the list of problem structures grew to include more than a thousand houses, a bridge and commercial buildings.

The website, the work of an engineering geologist named Tom St. John, includes case histories, a variety of references, and a summary spanning more than a decade of news coverage taken from two Canadian news outlets, La Presse, a website, and Le Nouvelliste, a newspaper.

The coverage begins in 2001 when a company called Laurentide Concrete received its first claims for problems related to deteriorating concrete. By 2009, a group called the Concrete Coalition (later the Coalition of Victims of Pyrrhotite) had been formed, and two years later Quebec announced a fund of $15 million, later expanded to $30 million, to help people with failing foundations.

According to the website’s summary, a legal battle that began in 2012 eventually resulted in a finding of liability mostly on the part of a concrete company and an engineering consultant of $196 million. The finding was appealed.

Last month, Prime Minister Justin Trudeau said the federal government would spend $30 million over three years to help homeowners. An advocates group believes as many as 4,000 homes may be affected, according to a news report.

Connecticut homeowners tell their stories

A website for a homeowners’ group called the Connecticut Coalition Against Crumbling Basements says that the homes with problematic concrete in northeastern Connecticut and southern Massachusetts were built in the 1980s and 1990s.

“The damage appears to take decades or more to appear, yet there is no magic number or formula to determine the rate at which a home will begin to fail, or when it will become unsound to inhabit,” the site says. “The date range of 1980 to 1998 is only a current estimate.”

The only solution appears to be a complete foundation replacement, and neither the state nor homeowners’ insurance companies have been much help.

A number of homeowners have posted their stories at the site, recalling expensive and unsuccessful attempts to patch cracking concrete, frustrating conversations with insurance companies, and financial and emotional distress.

“The company experts who patched our foundation told us the cracking would stop at some point, and they said their patching would fix the problem,” one homeowner wrote. “We paid them thousands of dollars for patching in 2013 and now the cracking has accelerated. We do not have much time left. I’m 61 years old and we wife is 59, and we are facing serious financial problems.”

Another wrote, “In 2012 I considered selling my duplex since the outside work and upkeep cost involved in being a landlord had become physically and financially excessive. It was quite a shock when my realtor told me my home was unsalable due to the crumbling concrete in the foundation of the rental side.

“I immediately contacted my insurance company, which informed me they would only cover a collapsed foundation, not one in the process of collapsing,” the account continues. “The irony is, since I reported the problem, I was no longer covered if the house did in fact collapse. In the mind of the insurance company, I was aware of the problem and did not correct it. ”

For a follow up to this report, check out this story in FineHomeBuilding’s sister site, Green Building Advisor. Follow GBA: @gbadvisor on Twitter | GreenBuildingAdvisor on Facebook.