Is self-binding gravel permeable?

Some are ✅, but many are not ❌

Many specifiers don’t realise a lot of self-binding (and some unbound gravels) are not permeable. They’re great materials for lightly trafficked applications. Versatile, sustainable, fantastic in rural locations and impactful in urban settings. 

To help the surface last, it needs adequate falls and drainage provision. Falls should be adequate, but not too steep ⛰️ 

Some suppliers recommend cross falls/camber of 1:40 and linear gradients no steeper than 1:15. 

The pictures show a couple of examples of recently installed pathways in parks near me which have suffered scour due to the steep gradient. Both are constructed with self-binding type gravel materials. 

The scour is caused by surface water run off travelling across the surface at high velocities. It leaves an uneven, unaesthetic and less accessible surface. 

A bound surface finish might have been a better option for these steep sections, or drainage provision to intercept overland flows and collect pathway runoff. 

If you’re unsure about material properties reach out to the supplier and if you need help with drainage or pavement design get in touch.