Blinding concrete is designed to provide a level platform for footings and slabs. It ensures that reinforcement can be tied correctly with the correct design concrete cover. It also reduces contamination of the rebar from the surrounding soil. Having a level blinding surface ensures formwork sits tight against it and reduces slurry loss during the concrete pour.
Blinding concrete usually has a nominated design strength of 25MPa and slump of 80mm, although at times design drawings do specify specific strength requirements. On-site concrete conformance testing is not required as it is a normal class mix and therefore is subject to the “Production Assessment” provisions of AS 1379 and is tested by the supplier. However, if the design drawings call for a specific concrete strength then the strength should be verified.
It is important to minimise foot traffic after the foundation has been prepared and tested as per the earthworks specifications so that the surface is not overly disturbed. Blinding shall not progress without the foundation preparation hold point being released.
- Blinding poured without the foundation prep hold point being released.
- Lack of care when finishing the surface can cause issues when setting the formwork to line and level.
- Uneven surface finishes causing inadequate cover for the reinforcement.
Quality Tips beam construction
- Ensure that the foundation is sufficiently prepared and approved by the Geotechnical Engineer (where required).
- Have areas approved and ready for blinding so you can use structural concrete from large pours as blinding to reduce wastage which is costly to dispose of.