Class 2, Class 3 or Roadbase? Choosing a Crushed Rock Base

Crushed rock is the layer under everything that lasts. Driveways, shed slabs, paver bases, paths — get this layer right and the surface above it stays where you put it. Get it wrong and you find out during the first wet winter. The four products people most often confuse are Class 2, Class 3, 20mm Roadbase and the recycled option, so here is what separates them.

Crushed Rock Class 2 20mm — the vehicle-rated one

Class 2 20mm is engineered to Australian standard specifications for pavement and sub-base construction. Its particle size distribution is controlled, which is what lets it compact into a dense, genuinely load-bearing layer.

Use it for: driveways, vehicle-rated sub-base, and pathway construction where cars will drive over it. If a vehicle will sit on it, this is the specification to ask for.

Crushed Rock Class 3 20mm — the economical alternative

Class 3 20mm is the same idea with a looser specification, and a lower price to match. It compacts reliably for everyday work; it just is not the product to specify where engineered load-bearing strength is required.

Use it for: pathways, light-duty driveways, and general fill.

20mm Roadbase — the builder's standard

20mm Roadbase is crushed rock blended with fines so it locks together tightly once compacted, resisting rutting and shifting under both vehicle and foot traffic.

Use it for: driveways, shed bases, under-paving sub-base and trench backfill. Water it and roll or plate-compact it and it goes firm.

Recycled 20mm Roadbase — same job, lower cost

Recycled 20mm Roadbase is made from crushed concrete and masonry, tested to meet engineering specifications for general construction use. It compacts well, provides a stable foundation, and keeps material out of landfill.

Use it for: driveways, sub-base and general fill where budget and sustainability both matter.

Which one, in one table

Job	Product
Driveway that takes vehicles	Class 2 20mm, or 20mm Roadbase
Garden path or light-duty drive	Class 3 20mm
Shed base or under-slab prep	20mm Roadbase
General fill on a budget	Recycled 20mm Roadbase
Trench backfill	20mm Roadbase or Recycled

How deep does the base need to be?

As a rough working guide: 75–100mm compacted for a garden path, 100–150mm for a paved patio, and 150mm or more for a driveway that will carry a car. Compaction reduces the loose depth by roughly 20 percent, so order for the loose volume, not the finished one — 100mm of finished base over 20m² is closer to 2.5m³ delivered than 2m³.

Compaction is not optional

Crushed rock only works if it is compacted in layers. Spread it 75mm at a time, wet it lightly, and run a plate compactor over each layer before adding the next. Tipping 200mm in one go and rolling the top of it gives you a firm crust over loose rock, which fails in the first year.

Browse the Crushed Rock collection or the wider Aggregates range. If you're not sure whether your job needs Class 2 or Class 3, call 1300 21 21 11 — it is a five-minute conversation that can save a rebuild.