Surface regularity - levelness and flatness
The surface profiles of a slab need to be controlled so that departures from a theoretical flat plane are limited to an extent appropriate to the planned use of the floor. Levelness and flatness tolerances define the allowable or permitted variation in of a floor surface. Surface regularity needs to be limited in two ways:
- Flatness, in order to limit for example the bumpiness
- Levelness, to ensure that the building as a whole can function satisfactorily.
Flatness relates to variations over short distances whereas levelness relates to variations over longer distances. These distances are not easily definable but traditionally, flatness is concerned with variations in the surface plane over much shorter distances, e.g. 300mm whereas levelness is concerned with the variations in surface ‘level’ over distances of around 3m.
The relation of the actual surface plane to the theoretical surface plane is often referred to as level to datum.