Concrete subfloors make up a large portion of the commercial substrates over which floors are installed. Flooring failures over concrete subfloors cost millions of dollars each year, and the pain of going through a replacement installation in an occupied space remains with the customer for some time. To mitigate these failures, we recommend following the recommendations for installation over concrete from the Guaranteed Installation Systems Manual (F-5061), which states, “New and existing concrete sub-floors must meet the requirements of the latest edition of ASTM F 710, ‘Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring.’” It’s a fair statement that simply following the guidelines in this standard would prevent a large number of flooring failures.
By its very nature, concrete starts as a water-saturated mass which must cure, then dry sufficiently. Concrete is a mixture of water, cement, and fine, medium and large aggregates. It can have any variety of additives depending on use and weather conditions when poured. Fly ash has been used for many years as an additive, typically comprising 15-20% of the cement mix. Higher percentages may sometimes be used, perhaps due to the desire for higher recycled content in mix designs. The reported effects of higher fly ash content are a slower initial strength gain and a slowed development of the carbonation layer of the slab surface.