Technical articles 5 min read
Choosing a fraction: one simple trade-off
The coarser the fraction, the lighter and the weaker. Grade selection is very nearly that one sentence.
As the particle gets larger, the ratio of pore space to solid material rises: the granule gets lighter and its crushing resistance falls.
For structural concrete, 4–10 mm usually strikes the best balance. For bulk fill and screeds, where strength is not the governing criterion, coarser is better. For blocks and mortars, where the finished surface matters, go fine.
One exception: in drainage applications the size is set by the permeability you need, not by weight — and there a uniform grading matters more than the absolute size.
For structural concrete, 4–10 mm usually strikes the best balance. For bulk fill and screeds, where strength is not the governing criterion, coarser is better. For blocks and mortars, where the finished surface matters, go fine.
One exception: in drainage applications the size is set by the permeability you need, not by weight — and there a uniform grading matters more than the absolute size.