Fly ash in concrete causing flooring installation failures

James Vallette | June 15, 2015 | Newsletter

Floor Trends magazine last week uploaded an enlightening video interview with consultant Lew Migliore (LGM & Associates). Migliore raised an issue that is just coming to light in the flooring industry: increasing proportions of fly ash in concrete underlayment are causing flooring installation failures.

“The fly ash issue has just escalated,” Migliore said. “Just recently, the American fly ash association and the concrete industry have come to some agreement where more can go into the concrete, which was a celebrated event for them. When you get up to about forty percent fly ash content, it starts to create issues of flooring materials not sticking to the surface of the concrete. Now, increasing that to upwards of 60%, the likelihood of you sticking anything to that floor becomes very remote.

“Who knows as a flooring contractor how much fly ash is in the concrete?” he asked. “No one thinks to ask that. When there’s a failure, somebody putting in the flooring’s going to be blamed for something the concrete people did.”

A search of the American Coal Ash Association website reveals no discussion of these issues. However, one flooring company, Metroflor, makes clear that its experience with installations on fly ash laden subfloors has been less than optimal. Its installation guide, published last year, includes this warning: 

Warning: Concrete Subfloors Containing Coal Fly Ash: Fly ash is routinely used in cement in LEED projects. No doubt it will continue to grow in popularity as LEED points become the norm in commercial construction. Fly ash contains silicon dioxide and calcium oxide. Silicon is difficult to bond to and calcium oxide is a caustic, alkaline by-product which plays havoc on flooring adhesives. Installing floors on concrete substrates containing coal fly ash can be problematic and therefore may require aggressive scarification or shot blasting prior to installation of flooring. 

Migliore described the increasing use of fly ash in concrete subfloors as “uncharted territory. You think you’re doing everything good, and it comes back and reacts in a way you never expected it to. There’s no history of any this stuff having been done, to know what effects it’s going to have on our industry.”

Last December, the US EPA gave a limited all-clear to the “beneficial” use of fly ash in concrete. However, as I discussed in two articles (1), its review was very limited in scope.  It only contemplated “encapsulated” and “fully cured” uses, not demolition, nor in-use pulverization scenarios such as the "shot blasting" suggested by Metroflor’s installation instructions. (2) Further, the mercury content of fly ash is increasing as air pollution control devices capture increasing amounts of the toxic heavy metal component of coal. (3)

Jim Vallette is senior researcher for the Healthy Building Network. Follow Jim on Twitter @HBNJim.

(1) See "Buyers Beware: Coal Ash in Building Products," Healthy Building News, Jan. 30, 2014 (available at:; and  "Dust in the Wind: EPA’s Vacuous Review of Coal Waste in Building Products," Pharos Signal, Feb. 28, 2014 (available at

(2) The EPA review only considered concrete and wallboard, not other, more friable, building products that have incorporated fly ash, such as ceiling tiles and carpets. 

(3) See my 2013 Pharos Signal article, "Air Pollution Control Boosts Mercury Levels in Coal Ash."