Alumasc answers their most frequently asked questions about concrete tolerance and deflections

Posted by Ashlea Williamson

Q1. Can Alumasc provide written confirmation that concrete tolerance and deflections noted within structural engineers report are suitable?

The acceptability of the level of deflection of a concrete deck is a matter for the client, the main contractor and the structural engineer to determine in accordance with the prevailing standards, regulations and codes of practice as identified in the National Structural Concrete Specification for Building Construction. Standard construction tolerances for concrete surfaces are generally acknowledged as having no deviation of more than 9mm over a 3m length, or any abrupt irregularities of more than 3mm. Deviations in excess of this definition are the responsibility of the client or their appointed agent to rectify.

Where deemed unsatisfactory, correction of any slab outside tolerance resulting in a negative fall would be recommended to ensure that all design parameters are sustained throughout the lifecycle of the roof, and should ideally be brought within standard construction tolerance and noted.

Q2. Can Alumasc provide a solution for the localised correction of concrete tolerance and/or deflection?

Alumasc Monoscreed is a fast curing PMMA based compound screed specifically engineered for this purpose. The cold applied compound can be mixed at roof level and applied from 3mm to 50mm in order to bring levels back to acceptable tolerance. The system is unaffected by ambient temperatures, is rainproof within 15 minutes of being applied and will fully cure in circa 45 minutes, thus offering significant programme benefits when compared with more traditional screeds.


For further information about Alumasc’s Monoscreed click here or contact our technical team on 03335 771 500

Deck deflection screed brochure download

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White House Works, Bold Road, Sutton, St Helens, Merseyside, WA9 4JG