Structural layers that make up the various types of every day trafficked surface

The thickness of each layer depends largely on the type of subgrade ie clay, soil etc and the type of traffic and its density that is going to use it.

The subase is normally Type 1 aggregate which will conform to specific grading and moisture requirements.

The road base can either be a coated material like the base and surface course or it can be a lean mix concrete. These days it is normally coated.

On drives and footpaths where the type of traffic is reasonable light is normal to do away with the Road Base.

Only in very special circumstances should the surface course be laid directly on to the subase. It should always be laid on to a base course.