Datum Levels or Surface Regularity

We often get into discussions around the quality associated with floor screeding projects. Unfortunately there are times when people are not able to understand each other because there are assumptions and there is confusion over the language being employed. One big area for dispute can occur when we are talking about ‘flatness’ and ‘levels’. We hope these definitions and diagrams will help.

According to the Screed Scientist Lexicon: 

  • Datum level: It is a fixed reference level or base against which the height of the flooring is measured.
  • Deviation from Datum: It is the deviation in the height of the surface of the layer of flooring from that of a fixed datum level.
  • Surface regularity: Surface regularity of screeds is a measure of the flatness of the screeded surface. Surface Regularity is popularly expressed as SR1, SR2 and SR3 with SR1 being floors that require the highest degree of flatness.

Surface Regularity Fail


Surface Regularity Pass


Departure from datum fail


Departure from Datum Pass

Now that we have the basic terms and diagrams defined and cleared in our heads we can move onto the interplay of these two very different concepts. These next two images show how we really need to be clear in our language.

Regularity Fail Datum Pass


Regularity Pass Datum Fail