Laitance is a major cause of failure in flooring installations. It takes the form of a weak, friable layer on the surface of concrete and sand cement screeds which appears after curing. It is made from cement and fine aggregates that rise to the surface when too much water is added. It may also be due to rain damage during placing, or from over trowelling. Subsequent poor curing of the surface will also contribute towards the formation of laitance.
Scrabbling, grinding and abrading are recommended for removing laitance.