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Finishes for composite slabs with steel decking

It is generally not possible to construct composite slabs to tight level to datum and flatness tolerances due to the deflection of the supporting beams and the flexibility of the steel decking. Thus tight tolerances should not be specified for the top surface. If tight surface regularity tolerances are required, it may be necessary to apply screeds or levelling compounds. Tolerances may also be influenced by the method of construction. In many buildings tight flatness and level tolerances will not be required as the composite slab will be covered by thicker floorings or raised access (computer) floors.

It should be possible to achieve a floor level to datum within ± 15mm around the columns. Elsewhere this may not be achieved, due to the flexibility of the slabs. SR1 flatness tolerances to BS 8204 are not achievable on composite floor slabs on steel decking and SR2 will be difficult to achieve. SR3(10mm under a 2m straight edge laid on the surface) may be achievable on areas of the floor, depending on deflections. Application of a levelling screed or smoothing underlayment may still be necessary.

Further reading: Concrete Society Technical Report 75, Composite concrete slabs with steel decking.

Acknowledgement: The Concrete Society

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Cracking in composite concrete slabs using metal decking

TR75 Composite concrete slabs using steel decking