In an ideal world, a concrete floor in a house for day old chicks should be minimum 30oC. With this temperature, a chick will stay warm even when the layer of litter is limited.
To achieve this temperature level (or a temperature as close to it as possible) we need to preheat our houses before placement of the chicks. Most people are aware that spreading out the litter should not be done before the floor is properly preheated, as the isolation of the layer of straw or woodshavings will prevent an adequate warming of the floor.
But not everybody realizes that preheating cannot be done when the floors are still wet. When the houses are cleaned and washed down, they need energy to dry. If there is water remaining on the floors, the floors will not warm up until the water is evaporated, which can take a significant time.
This means that the time of preheating should be calculated from the moment the floors (houses) are dry, and not from the time the temperature is put on the level for preheating. In practice this means that when the water is not adequately removed after cleaning, a lot of time and energy is wasted on drying the floors, instead of preheating them.
Preheating wet floor will result in colder floors then expected, and will result in cold chicks as well.