Use this as a quick guide. Local codes and engineer’s specs must always take priority.
| 15 MPa | Blinding layers, non-structural fill, kerbs, garden paths, leveling concrete where strength is not critical. |
|---|---|
| 20 MPa | Light-duty driveways and paving, pathways with light traffic, small non-loadbearing slabs (sheds, walkways). |
| 25 MPa | Typical house slabs, beams and columns, garage slabs, light industrial floors, most general structural work for low-rise buildings. |
| 30 MPa | More heavily loaded slabs and beams, higher quality floors, small suspended slabs, areas with higher load or durability requirements. |
| 35–40 MPa | Heavily loaded industrial floors, columns and beams with high loads, precast elements, bases under heavy machinery, and structures with strict durability requirements. |
6–13 mm: Thin toppings, screeds, repair layers, or where there is congested steel.
19 mm: Common “standard” size for most house slabs, beams and columns.
26 mm: Thicker sections and some mass concrete where cover and spacing allow.
Aim for the lowest slump that still allows proper placing and compaction. If the mix is too stiff, rather use a plasticiser admixture than just adding water, to avoid losing strength.