Q.: A flooring contractor has experienced problems on four occasions over the years with his two-part polyurethane floor covering not bonding to our concrete slab-on-grade. He has said that the acid-etch process prior to installing the covering did not react very well with our slab surface, based on his observation of the amount of bubbling. He also reports a strong ammonia smell emitted from our concrete as well as a darker appearance of the concrete throughout the depth of the slab. The flooring contractor did not run vapor emission tests on any of these jobs. He was confident he had waited long enough for vapor emission to not be a problem.
As the concrete supplier, I am convinced that unless you run vapor emission tests that indicate the emission is below the maximum limit for his product, you are asking for bonding problems. Supposedly the general contractor installed a vapor barrier for the slab-on-grade. The flooring contractor does not believe a hydrostatic head exists under the slab. Water was present in the failed areas.
The flooring contractor is convinced that something in our concrete caused his problems. Are you aware of any other factors that we need to investigate related to this type problem?
A.: This is an ongoing problem of concern to not only the concrete industry but also to the flooring industry. Hanley-Wood, LLC, which publishes this magazine as well as CONCRETE CONSTRUCTION, cosponsored a meeting of the newly convened "Inter Industry Working Group (IIWG) on Concrete Floor Issues" April 17–18 in Chicago. More than 40 people attended representing professional and technical associations, specifiers and designers, flooring industry groups, flooring contractors, and manufacturers. Other co-sponsors included Construction Technology Laboratories, which also organized and hosted the meeting; the American Society of Concrete Contractors; and the Strategic Development Council of the ACI Concrete Research and Education Foundation.
The significance of this gathering is that it brought together, for the first time, representatives of diverse organizations that traditionally had been pointing fingers at each other. Now, rather than trying to simply assess blame, these groups are working together to find solutions to the problems associated with placing various flooring materials on concrete slabs and then develop methods for producing better floors. A follow-up meeting is in the planning stages.
While the preliminary report of the April meeting has not yet been released, several key points were clear. First, impermeable flooring placed on concrete slabs where the moisture level remains “too high” is a problem waiting to happen. There also was general agreement on the importance of measuring the moisture content before applying the flooring, but the industry needs to develop and agree upon better ways of both measuring and controlling that moisture.
And finally, the growth of fast-track construction—where concrete strength gain is considered but slab moisture content generally is not—is causing significant problems for all players in the industry.
Now, returning to the original question, the description of this installation raises several red flags. First, an acid wash is not sufficient surface preparation for placing a polyurethane floor on concrete. To learn what is, check "Guidelines for Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and Polymer Overlays." It is available from the International Concrete Repair Institute (www.icri.org).
Beyond that, urethane is known to not bond well to concrete. Applying a layer or two of epoxy as an undercoat may go a long way toward solving this particular problem in future installations.
Then, of course, there is the moisture issue. Based on the discussions at the IIWG meeting, you are correct: Flooring should never be installed without checking the moisture level of the concrete. Elapsed time is far less important than other environmental conditions in determining how rapidly water vapor will escape from the slab. And if water vapor continues to enter the slab due to the absence of, or problems with, a vapor barrier, vapor emission testing will bear that out as well.
The ammonia smell might indicate the presence of some fly ash in the mix. If that were the case, it might also slow the slab’s drying but should not otherwise adversely affect the installation. And the "darker appearance through the depth of the slab" would seem to indicate, if nothing else, a higher moisture level in those darker areas. Unfortunately that would be consistent with the bonding problems that arose with the polyurethane. In considering whether the conditions are appropriate for installing his floor, the flooring contractor should reconsider his confidence in having "waited long enough" and rely more on testing and observation.