6F2 & 6F5 Capping Material — The Complete Guide

6F2 and 6F5 are specialist capping materials used in road construction and large-scale groundworks. If you're working on major infrastructure or road building, you need to know the difference.

What is 6F2 & 6F5 Capping Material?

6F2 and 6F5 are both granular capping materials used in highway construction under the sub-base layer. They consist of crushed concrete, crushed rock, or recycled materials graded to specific requirements. 6F2 is a finer, more controlled material, while 6F5 allows larger particles and is coarser. Both are used to improve ground bearing capacity and provide a stable platform for sub-base construction above weak or variable subgrade.

Common uses

Road and highway construction (capping layer)
Large commercial groundworks
Improving bearing capacity of weak subgrade
Embankment fill material
Large-scale industrial hardstanding base
Infrastructure projects and civils

Sizes & grades

6F2: 0–100mm (controlled grading). 6F5: 0–125mm (coarser, less controlled). Both specified under the Highways England Manual of Contract Documents for Highway Works (MCHW).

How much do you need?

Capping layers are typically 150–600mm thick depending on subgrade CBR (California Bearing Ratio). Calculate volume × 2.1 tonnes/m³. Capping is almost always a specification-driven quantity calculated by a civil engineer.

Pro tip

6F2 and 6F5 are specification materials — always check your project drawings and specification before ordering. Substituting one for the other without engineer approval can invalidate warranties and approvals.