Be careful with coatings on concrete with more than 20% fly ash.
Texcrete Be careful with coatings on concrete with more than 20% fly ash.

Question: Also from CC’s LinkedIn discussion group came this question: Can concrete with high percentages of fly ash or slag create a problem when installing a polymer overlay?

Answer: Bud Earley, concrete restoration specialist at Mapei, responded: Before doing anything I would find out what percentage of fly ash was used in the concrete. There have been problems with floors that get over the 15 to 20 percent range. Surface preparation becomes more critical as the fly ash percentage goes up. Take extra care when preparing the surface and do a mock-up test area of sufficient size and then test for adhesion. The best resource for this is the International Concrete Repair Institute’s Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and Polymer Overlays (310.2-1997). If you have an adhesion test performed, make sure it’s done according to ICRI 210.3-2004, Guide for Using In-Situ Tensile Pull-Off Test to Evaluate Bond of Concrete Surface Materials.