How Much Do You Need and How Do You Spec It Right?
Class II Aggregate Base is one of the most ordered products at any quarry serving construction in California — and also one of the most frequently under-specified on smaller projects. Get the compaction rate wrong, or order short, and you’re looking at a second delivery and a delayed pour.
This article covers the practical side of working with Class II base: what it is, how to estimate quantity, what compaction to expect, and when it’s the right product versus when something else would serve you better.
What Is Class II Base?
Class II Aggregate Base (also called CAB or Class II AB) is a crushed aggregate that conforms to Caltrans Standard Specification Section 26. In plain terms: it’s a well-graded crushed rock blend — typically 3/4-inch minus — that includes a controlled percentage of fines. Those fines are what give Class II its compaction behavior. When properly moisture-conditioned and compacted, the fine particles fill the voids between larger pieces and the whole mass densifies into a stable, load-bearing layer.
This is what goes under roads, driveways, parking lots, building slabs, concrete flatwork, and most other paved or semi-paved surfaces in California. It’s a Caltrans-compliant product, which matters on public projects and on private jobs where an inspector is involved.
How Much Class II Base Do You Need?
The standard formula:
Tons needed = (Length × Width × Depth in feet × Unit weight) ÷ 2,000
For Class II granite aggregate, the typical compacted unit weight is around 130–135 lbs per cubic foot. However, you’re ordering in loose volume and it will compact down — typically 15–20% compaction factor depending on your lift thickness and equipment.
As a practical rule of thumb:
- At a 4-inch compacted depth: approximately 55–60 square feet per ton
- At a 6-inch compacted depth: approximately 36–40 square feet per ton
- At a 8-inch compacted depth: approximately 27–30 square feet per ton
Always add 10–15% overage to your order. Subgrade irregularities, edge waste, and the difference between loose and compacted volume will eat into your numbers faster than expected, especially on larger pads.
Example: A 10,000 sq ft parking lot at 6-inch compacted Class II base needs roughly 250–280 tons before overage. Call it 300 tons to be safe.
Compaction Requirements
Caltrans specifies 95% relative compaction for Class II base under most roadway applications. For private projects, your project engineer may call out 90% or 95% depending on the loading scenario.
A few practical notes on hitting those numbers:
Moisture content matters. Class II compacts best near its optimum moisture content — typically 6–9% for most granite-based material. Too dry and you won’t get density; too wet and you’ll get pumping under the roller. If you’re working in the high desert in summer, you may need to water the material on the grade before compacting.
Lift thickness. Standard practice is compacting in 4-inch lifts maximum for most vibratory plate or drum roller equipment. Thicker lifts can leave uncompacted zones at depth that won’t show up on a nuclear gauge test until the slab starts settling.
Subgrade prep first. Class II base is only as good as what’s under it. A soft or non-uniform subgrade will undermine your compaction results regardless of how well you work the base. Scarify, moisture condition, and proof-roll the native material before placing.
When Class II Base Is the Right Product
Class II is appropriate when you’re paving — concrete or asphalt — and need a Caltrans-spec base, when your project requires a compaction test and documentation, when you need a product that will support significant dead and live loads over time, or when the design calls for a uniform, stable platform such as slabs, footings, or flatwork.
When to Consider Something Else
Open-graded base is used when drainage through the base layer is a design requirement — under permeable pavers, for example, or in areas with poor native drainage. It sacrifices some load-bearing capacity for drainage performance. Class II is not a drainage product.
Native subgrade with geotextile is sometimes used on very large, lightly-loaded areas like unpaved storage yards where full Class II depth would be cost-prohibitive. Not a substitute for structural applications.
Crusher fines / decomposed granite works for pathways and light-duty surfaces but won’t perform under vehicular loads.
Class II Base in the High Desert
Lynx Cat Mountain Quarry produces Caltrans-compliant Class II Aggregate Base from hard granite near Barstow. We can provide gradation certifications and material submittals for jobs that require them — which matters on military, municipal, and DOT projects in the Barstow, Fort Irwin, and China Lake corridor.
We haul throughout the Southern California high desert. If you’re putting together a bid or need a quick quantity check, call our team directly.
760-760-5969 | quotes@lcmquarry.com
