Departure from Datum
Depending on the intended use and the area to be screeded, it is important to specify the maximum permissible departure of the level of the finished surface from an agreed datum plane, right at the design stage of a screeding project. As per the British Standards Code of Practice, a departure of up to 15mm is considered satisfactory for large areas. However, the permissible departure from datum is much lower for smaller areas, and high levels of accuracy is essential for small rooms, along the line of partition walls, in the vicinity of door openings and in areas where specialized instruments are to be placed directly on the floor.
Level surveying for assessing the departure from datum can be done to high levels of accuracy with modern electronic ‘total stations’. In addition to yielding highly accurate measurements, these instruments also help to eliminate manual errors in log keeping by facilitating electronic storage of survey results. Rotary laser level is also common levelling equipment that is used for achieving high accuracy results.
The accurate measurement of levels for screeds and substrate levels play a major role in controlling the costs and ensuring high quality standards for the screed. Level survey measurements are generally required for:
- Assessing the level of concrete substrates before commencing screed installation
- Assessing the departure from datum of screed after installation
- Measuring the average level of the installed screed
Right from determining the minimum /maximum depth requirements of screed and ensuring the compliance of screed levels with initial specifications to settling disputes regarding deviation against contract, accurate level surveying is a crucial aspect in screeding projects.
When an inaccurate assessment of level of the concrete substrate could lead to a wrong estimation of screed depth which in turn could translate into- higher concrete, higher costs and longer drying period in case the assessed level is lower than the actual measurement; a higher assessed level than the actual level could lead to judgements of lower screed depth, which can drastically affect the quality and integrity of the screed.