We would like to know what the formulation of concrete fills placed over structural slabs should be so that the installation of thin-set floor coverings such as epoxy, neoprene, acrylic, etc. will be crack-free.
The trouble with fill concrete is that very little attention is given to its installation. In general, rather lean mixes are used that have a high water content, the concrete is seldom cured, and upon evaporation of the superfluous water, shrinkage cracks occur. The best solution would be to finish the structural slab to the required grade and have it troweled to a smooth surface free from whirls and ridges. Protection against early drying would reduce cracking to a minimum.