The delamination of the surface layer of concrete floors during or after the surface finishing actions (floating, troweling, polishing) is no new phenomenon. However increased numbers of cases have been observed these last years. In currently encountered cases, two main causes for delamination have been observed: an excess of entrapped or entrained air in the concrete and late bleeding. The timing of the start of the finishing operation is also crucial (notion of 'window of finishability'). A slow setting-time or crusting of the surface of the concrete can complicate the determination of the optimal finishing time. The influence on the air-content, the bleeding-rate and the hardening properties of concrete of different concrete constituents is being investigated in this research project. The first results are presented and some previsional practical recommendations are given.