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Due to the inherent and allowable design deflections of the steel framework and metaldeck systems, it is not possible to install composite suspended slabs to fixed datum points. Datum levels will only be relevant at fixed points such as beam and column junctions.
For more information on this, we recommend reviewing Pages 27 - 29 of the MCRMA/SCI technical guide "P300 Composite Slabs and Beams Using Steel Decking: Best Practice for Designed Construction". A PDF version of this document is available for download here.
The surface tolerance is dictated by the finish that is applied to the slab and tight flatness tolerances are only achievable if the deflection of the supporting beam are limited by the design.
An easyfloat or skipfloat finish can provide an SR3 surface tolerance over large areas of the floor slab. SR3 to part 1 of BS8204 is defined as a 10mm deviation under a calibrated 2 metre straight edge.
Where an easyfloat or powerfloat finish has been specified, the application of a leveling compound may still be necessary prior to the installation of the specified floor finishes.